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Xue G, Qin B, Ma C, Yin P, Liu C, Liu K. Large-Area Epitaxial Growth of Transition Metal Dichalcogenides. Chem Rev 2024. [PMID: 39132950 DOI: 10.1021/acs.chemrev.3c00851] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/13/2024]
Abstract
Over the past decade, research on atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) has expanded rapidly due to their unique properties such as high carrier mobility, significant excitonic effects, and strong spin-orbit couplings. Considerable attention from both scientific and industrial communities has fully fueled the exploration of TMDs toward practical applications. Proposed scenarios, such as ultrascaled transistors, on-chip photonics, flexible optoelectronics, and efficient electrocatalysis, critically depend on the scalable production of large-area TMD films. Correspondingly, substantial efforts have been devoted to refining the synthesizing methodology of 2D TMDs, which brought the field to a stage that necessitates a comprehensive summary. In this Review, we give a systematic overview of the basic designs and significant advancements in large-area epitaxial growth of TMDs. We first sketch out their fundamental structures and diverse properties. Subsequent discussion encompasses the state-of-the-art wafer-scale production designs, single-crystal epitaxial strategies, and techniques for structure modification and postprocessing. Additionally, we highlight the future directions for application-driven material fabrication and persistent challenges, aiming to inspire ongoing exploration along a revolution in the modern semiconductor industry.
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Affiliation(s)
- Guodong Xue
- State Key Laboratory for Mesoscopic Physics, Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University, Beijing 100871, China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
| | - Biao Qin
- State Key Laboratory for Mesoscopic Physics, Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University, Beijing 100871, China
| | - Chaojie Ma
- State Key Laboratory for Mesoscopic Physics, Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University, Beijing 100871, China
| | - Peng Yin
- Key Laboratory of Quantum State Construction and Manipulation (Ministry of Education), Department of Physics, Renmin University of China, Beijing 100872, China
| | - Can Liu
- Key Laboratory of Quantum State Construction and Manipulation (Ministry of Education), Department of Physics, Renmin University of China, Beijing 100872, China
| | - Kaihui Liu
- State Key Laboratory for Mesoscopic Physics, Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University, Beijing 100871, China
- International Centre for Quantum Materials, Collaborative Innovation Centre of Quantum Matter, Peking University, Beijing 100871, China
- Songshan Lake Materials Laboratory, Dongguan 523808, China
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2
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Valenti A, Calvera V, Kivelson SA, Berg E, Huber SD. Nematic Metal in a Multivalley Electron Gas: Variational Monte Carlo Analysis and Application to AlAs. PHYSICAL REVIEW LETTERS 2024; 132:266501. [PMID: 38996276 DOI: 10.1103/physrevlett.132.266501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 01/17/2024] [Accepted: 04/26/2024] [Indexed: 07/14/2024]
Abstract
The two-dimensional electron gas is of fundamental importance in quantum many-body physics. We study a minimal extension of this model with C_{4} (as opposed to full rotational) symmetry and an electronic dispersion with two valleys with anisotropic effective masses. Electrons in our model interact via Coulomb repulsion, screened by distant metallic gates. Using variational Monte Carlo simulations, we find a broad intermediate range of densities with a metallic valley-polarized, spin-unpolarized ground state. Our results are of direct relevance to the recently discovered "nematic" state in AlAs quantum wells. For the effective mass anisotropy relevant to this system, m_{x}/m_{y}≈5.2, we obtain a transition from an anisotropic metal to a valley-polarized metal at r_{s}≈12 (where r_{s} is the dimensionless Wigner-Seitz radius). At still lower densities, we find a (possibly metastable) valley and spin-polarized state with a reduced electronic anisotropy.
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3
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Krizman G, Bermejo-Ortiz J, Zakusylo T, Hajlaoui M, Takashiro T, Rosmus M, Olszowska N, Kołodziej JJ, Bauer G, Guldner Y, Springholz G, de Vaulchier LA. Valley-Polarized Quantum Hall Phase in a Strain-Controlled Dirac System. PHYSICAL REVIEW LETTERS 2024; 132:166601. [PMID: 38701448 DOI: 10.1103/physrevlett.132.166601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 02/21/2024] [Accepted: 03/27/2024] [Indexed: 05/05/2024]
Abstract
In multivalley systems, the valley pseudospin offers rich physics going from encoding of information by its polarization (valleytronics), to exploring novel phases of matter when its degeneracy is changed. Here, by strain engineering, we reveal fully valley-polarized quantum Hall phases in the Pb_{1-x}Sn_{x}Se Dirac system. Remarkably, when the valley energy splitting exceeds the fundamental band gap, we observe a "bipolar quantum Hall phase," heralded by the coexistence of hole and electron chiral edge states at distinct valleys in the same quantum well. This suggests that spatially overlaid counterpropagating chiral edge states emerging at different valleys do not interfere with each other.
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Affiliation(s)
- G Krizman
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - J Bermejo-Ortiz
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, 24 rue Lhomond 75005 Paris, France
| | - T Zakusylo
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - M Hajlaoui
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - T Takashiro
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - M Rosmus
- National Synchrotron Radiation Centre SOLARIS, Jagiellonian University, Czerwone Maki 98, 30-392 Krakow, Poland
| | - N Olszowska
- National Synchrotron Radiation Centre SOLARIS, Jagiellonian University, Czerwone Maki 98, 30-392 Krakow, Poland
| | - J J Kołodziej
- National Synchrotron Radiation Centre SOLARIS, Jagiellonian University, Czerwone Maki 98, 30-392 Krakow, Poland
- Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Krakow, Poland
| | - G Bauer
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - Y Guldner
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, 24 rue Lhomond 75005 Paris, France
| | - G Springholz
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - L-A de Vaulchier
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, 24 rue Lhomond 75005 Paris, France
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4
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Fan G, Wu Y, Tong J, Deng L, Yin X, Tian F, Zhang X. Influence of electronic correlation on the valley and topological properties of VSiGeP 4 monolayer. Phys Chem Chem Phys 2024; 26:9628-9635. [PMID: 38466239 DOI: 10.1039/d3cp04739c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
Valley is used as a new degree of freedom for information encoding and storage. In this work, the valley and topological properties of the VSiGeP4 monolayer were studied by adjusting the U value based on first-principles calculations. The VSiGeP4 monolayer remains in a ferromagnetic ground state regardless of the change in the U value. The magnetic anisotropy of the VSiGeP4 monolayer is initially in-plane, and then turns out-of-plane with the increase in the U value. Moreover, a topological phase transition is observed in the present VSiGeP4 monolayer with the increase in U value from 0 to 3 eV, i.e., the VSiGeP4 monolayer behaves as a bipolar magnetic semiconductor, a ferrovalley semiconductor, a half-valley metal characteristic, and a quantum anomalous Hall state. The mechanism of the topological phase transition behavior of the VSiGeP4 monolayer was analyzed. It was found that the variation in U values would change the strength of the electronic correlation effect, resulting in the valley and topological properties. In addition, carrier doping was studied to design a valleytronic device using this VSiGeP4 monolayer. By doping 0.05 electrons per f.u., the VSiGeP4 monolayer with a U value of 3 eV exhibits 100% spin polarization. This study indicates that the VSiGeP4 monolayer has potential applications in spintronic, valleytronic, and topological electronic nanodevices.
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Affiliation(s)
- Guangxin Fan
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Yanzhao Wu
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Junwei Tong
- Department of Physics, Freie Universität Berlin, Berlin 14195, Germany
| | - Li Deng
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Xiang Yin
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Fubo Tian
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Xianmin Zhang
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
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Chen M, Kong X, Xie X, Liu X, Li J, Peeters FM, Li L. Tunable valley polarization effect and second-order topological state in monolayer FeClSH. Phys Chem Chem Phys 2024; 26:3285-3295. [PMID: 38197170 DOI: 10.1039/d3cp05127g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2024]
Abstract
In two-dimensional (2D) materials, breaking the inversion symmetry plays an important role in valleytronics. Ferrovalley (FV) materials can achieve spontaneous valley polarization (VP) without additional modulation due to the magnetic exchange interaction and strong spin-orbit coupling. Using first-principles calculations, we predict a new 2D material, Janus FeClSH, which exhibits a large spontaneous VP. This monolayer is a perfect FV material, where the valence band maximum and conduction band minimum are located at the K/K' point. A large VP of 102.95 meV is spontaneously generated for the case of out-of-plane magnetization. Additionally, we propose that the irradiating circularly polarized light can be used to realize VP for the case of in-plane magnetization. Remarkably, a triangular nanoflake of FeClSH with armchair edges can show nontrivial corner states, exhibiting a second-order topological insulator (SOTI) state. The VP effect and SOTI state are tunable with the Hubbard U parameter, making the FeClSH monolayer promising for the study of the coupling between VP and SOTI.
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Affiliation(s)
- Mengteng Chen
- School of Science, Hebei University of Technology, Tianjin 300401, China.
| | - Xiangru Kong
- College of Sciences, Northeastern University, Shenyang 110819, China.
| | - Xiao Xie
- School of Science, Hebei University of Technology, Tianjin 300401, China.
| | - Xiaobiao Liu
- School of Science, Henan Agricultural University, Zhengzhou 450002, China
| | - Jia Li
- School of Science, Hebei University of Technology, Tianjin 300401, China.
| | - François M Peeters
- Centre for Quantum Metamaterials, HSE University, Moscow 101000, Russia
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, 60455-760 Fortaleza, Ceará, Brazil
| | - Linyang Li
- School of Science, Hebei University of Technology, Tianjin 300401, China.
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6
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Man P, Huang L, Zhao J, Ly TH. Ferroic Phases in Two-Dimensional Materials. Chem Rev 2023; 123:10990-11046. [PMID: 37672768 DOI: 10.1021/acs.chemrev.3c00170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/08/2023]
Abstract
Two-dimensional (2D) ferroics, namely ferroelectric, ferromagnetic, and ferroelastic materials, are attracting rising interest due to their fascinating physical properties and promising functional applications. A variety of 2D ferroic phases, as well as 2D multiferroics and the novel 2D ferrovalleytronics/ferrotoroidics, have been recently predicted by theory, even down to the single atomic layers. Meanwhile, some of them have already been experimentally verified. In addition to the intrinsic 2D ferroics, appropriate stacking, doping, and defects can also artificially regulate the ferroic phases of 2D materials. Correspondingly, ferroic ordering in 2D materials exhibits enormous potential for future high density memory devices, energy conversion devices, and sensing devices, among other applications. In this paper, the recent research progresses on 2D ferroic phases are comprehensively reviewed, with emphasis on chemistry and structural origin of the ferroic properties. In addition, the promising applications of the 2D ferroics for information storage, optoelectronics, and sensing are also briefly discussed. Finally, we envisioned a few possible pathways for the future 2D ferroics research and development. This comprehensive overview on the 2D ferroic phases can provide an atlas for this field and facilitate further exploration of the intriguing new materials and physical phenomena, which will generate tremendous impact on future functional materials and devices.
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Affiliation(s)
- Ping Man
- Department of Chemistry and Center of Super-Diamond & Advanced Films (COSDAF), City University of Hong Kong, Kowloon, Hong Kong 999077, P. R. China
- City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, P. R. China
| | - Lingli Huang
- Department of Chemistry and Center of Super-Diamond & Advanced Films (COSDAF), City University of Hong Kong, Kowloon, Hong Kong 999077, P. R. China
- City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, P. R. China
| | - Jiong Zhao
- Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong 999077, P. R. China
- The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, P. R. China
| | - Thuc Hue Ly
- Department of Chemistry and Center of Super-Diamond & Advanced Films (COSDAF), City University of Hong Kong, Kowloon, Hong Kong 999077, P. R. China
- City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, P. R. China
- Department of Chemistry and State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong 999077, P. R. China
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7
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Shrestha S, Li M, Park S, Tong X, DiMarzio D, Cotlet M. Room temperature valley polarization via spin selective charge transfer. Nat Commun 2023; 14:5234. [PMID: 37633986 PMCID: PMC10460417 DOI: 10.1038/s41467-023-40967-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 08/17/2023] [Indexed: 08/28/2023] Open
Abstract
The two degenerate valleys in transition metal dichalcogenides can be used to store and process information for quantum information science and technology. A major challenge is maintaining valley polarization at room temperature where phonon-induced intervalley scattering is prominent. Here we demonstrate room temperature valley polarization in heterostructures of monolayer MoS2 and naphthylethylammine based one-dimensional chiral lead halide perovskite. By optically exciting the heterostructures with linearly polarized light close to resonance and measuring the helicity resolved photoluminescence, we obtain a degree of polarization of up to -7% and 8% in MoS2/right-handed (R-(+)-) and left-handed (S-(-)-) 1-(1-naphthyl)ethylammonium lead iodide perovskite, respectively. We attribute this to spin selective charge transfer from MoS2 to the chiral perovskites, where the perovskites act as a spin filter due to their chiral nature. Our study provides a simple, yet robust route to obtain room temperature valley polarization, paving the way for practical valleytronics devices.
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Affiliation(s)
- Shreetu Shrestha
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA.
| | - Mingxing Li
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA
| | - Suji Park
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA
| | - Xiao Tong
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA
| | - Donald DiMarzio
- Northrop Grumman Corporation, One Space Park, Redondo Beach, CA, 90278, USA
| | - Mircea Cotlet
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA.
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8
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Ma Y, Wu Y, Tong J, Deng L, Yin X, Zhou L, Han X, Tian F, Zhang X. Distinct ferrovalley characteristics of the Janus RuClX (X = F, Br) monolayer. NANOSCALE 2023; 15:8278-8288. [PMID: 37078633 DOI: 10.1039/d3nr00346a] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Two-dimensional ferrovalley materials should simultaneously possess three characteristics, that is, a Curie temperature beyond atmospheric temperature, perpendicular magnetic anisotropy, and large valley polarization for potential commercial applications. In this report, we predict two ferrovalley Janus RuClX (X = F, Br) monolayers by first-principles calculations and Monte Carlo simulations. The RuClF monolayer exhibited a valley-splitting energy as large as 194 meV, perpendicular magnetic anisotropy energy of 187 μeV per f.u., and Curie temperature of 320 K. Thus, spontaneous valley polarization at room temperature will be present in the RuClF monolayer, which is nonvolatile for spintronic and valleytronic devices. Although the valley-splitting energy of the RuClBr monolayer was as high as 226 meV with magnetic anisotropy energy of 1.852 meV per f.u., the magnetic anisotropy of the RuClBr monolayer was in-plane, and its Curie temperature was only 179 K. The orbital-resolved magnetic anisotropy energy revealed that the interaction between the occupied spin-up states of dyz and the unoccupied spin-down states of dz2 dominated the out-of-plane magnetic anisotropy in the RuClF monolayer, but the in-plane magnetic anisotropy of the RuClBr monolayer was mostly contributed by the coupling of the dxy and dx2-y2 orbitals. Interestingly, the valley polarizations in the Janus RuClF and RuClBr monolayers appeared in their valence band and conduction band, respectively. Thus, two anomalous valley Hall devices are proposed using the present Janus RuClF and RuClBr monolayers with hole and electron doping, respectively. This study provides interesting and alternative candidate materials for the development of valleytronic devices.
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Affiliation(s)
- Yubiao Ma
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang, 110819, China.
| | - Yanzhao Wu
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang, 110819, China.
| | - Junwei Tong
- Department of Physics, Freie Universität Berlin, Berlin, 14195, Germany
| | - Li Deng
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang, 110819, China.
| | - Xiang Yin
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang, 110819, China.
| | - Lianqun Zhou
- Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou 215163, China
| | - Xiaoli Han
- Taian Weiye Electromechanical Technology Co., Ltd., Taian, 271000, China
| | - Fubo Tian
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun, 130012, China
| | - Xianmin Zhang
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang, 110819, China.
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9
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Zhang T, Xu X, Huang B, Dai Y, Kou L, Ma Y. Layer-polarized anomalous Hall effects in valleytronic van der Waals bilayers. MATERIALS HORIZONS 2023; 10:483-490. [PMID: 36196974 DOI: 10.1039/d2mh00906d] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The layer-polarized anomalous Hall effect (LP-AHE), derived from the coupling between the Berry curvature and the layer degree of freedom, is of importance for both fundamental physics and device applications. Nonetheless, the current research paradigm is rooted in topological systems, rendering such a phenomenon rather scarce. Here, through model analysis, we propose an alternative, but general, mechanism for realizing the LP-AHE in valleytronic van der Waals bilayers by interlayer sliding. The interaction between out-of-plane ferroelectricity and A-type antiferromagnetism gives rise to the layer-locked Berry curvature and thus the long-sought LP-AHE in bilayer systems. The LP-AHE can be strongly coupled with sliding ferroelectricity, rendering it ferroelectrically controllable and reversible. The mechanism is demonstrated in a series of real valleytronic materials, including bilayer VSi2P4, VSi2N4, FeCl2, RuBr2 and VClBr. The new mechanism and phenomena provide a significant new direction to realize the LP-AHE and explore its application in electronics.
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Affiliation(s)
- Ting Zhang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China.
| | - Xilong Xu
- School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Garden Point Campus, Brisbane, Queensland 4001, Australia
| | - Baibiao Huang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China.
| | - Ying Dai
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China.
| | - Liangzhi Kou
- School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Garden Point Campus, Brisbane, Queensland 4001, Australia
| | - Yandong Ma
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China.
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Li X, Yang C, Xia Y, Zeng X, Shen P, Li L, Xu F, Cai D, Wu Y, Wu Z, Li S, Kang J. Nonvolatile Electrical Valley Manipulation in WS 2 by Ferroelectric Gating. ACS NANO 2022; 16:20598-20606. [PMID: 36414329 DOI: 10.1021/acsnano.2c07469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Valleytronics in transition metal dichalcogenides has been intensively investigated for potential applications in next-generation information storage, data processing, and signal transmission devices. Here a ferroelectric gating approach is engaged in achieving nonvolatile electrical tuning of the valley-excitonic properties of monolayer and bilayer WS2. The gating effects include carrier doping and ferroelectric coupling, which are further distinguished by comparing two geometries where the gate electrodes are in direct contact with or insulated from the WS2 crystal. The results show that the carrier doping from gate electrodes acts on WS2 through carrier screening, which only moderately alters the valley polarization. In contrast, the ferroelectric gating promotes electron-phonon interaction, introduces a strong surface polarization field, and controls the interfacial charge trapping/detrapping, causing a Stark shift in exciton energy and strongly enhancing room-temperature valley polarization. In bilayer WS2, the intralayer-interlayer exciton transition is further induced, contributing to even higher valley polarization. The ferroelectric coupling effect can still be maintained after the removal of gate voltage, showing its nonvolatile nature. The role of ferroelectricity is further verified by the anomalous temperature dependence in valley polarization. This work has revealed effective electrical control over valley excitons in semiconductors through interaction with ferroelectric materials. The reported high room-temperature valley polarization in WS2 will boost the development of valleytronics devices.
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Affiliation(s)
- Xu Li
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Chengbiao Yang
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Yuanzheng Xia
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Xinlong Zeng
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Peng Shen
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Linglong Li
- School of Physics, Southeast University, Nanjing211189, P.R. China
| | - Feiya Xu
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Duanjun Cai
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Yaping Wu
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Zhiming Wu
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Shuping Li
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
| | - Junyong Kang
- Department of Physics, Engineering Research Center for Micro-Nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Jiujiang Research Institute, Xiamen University, Xiamen361005, P.R. China
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11
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Shi Y, Jia N, Cai J, Lyu Z, Liu Z. 2D electrene LaH 2monolayer: an ideal ferrovalley direct semiconductor with room-temperature ferromagnetic stability. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:475303. [PMID: 36179704 DOI: 10.1088/1361-648x/ac96bb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2022] [Accepted: 09/30/2022] [Indexed: 06/16/2023]
Abstract
In developing nonvolatile valleytronic devices, ferromagnetic (FM) ferrovalley semiconductors are critically needed due to the existence of spontaneous valley polarization. At present, however, the known real materials have various drawbacks towards practical applications, including the in-plane FM ground state, low Curie temperature (TC), small valley polarization, narrow energy window with clean polarized valley, and indirect bandgap. From first-principles calculations, here we predict anideal ferrovalley semiconductor, honeycomb LaH2monolayer (ML), whose intrinsic properties can overcome all these shortcomings. We demonstrate that LaH2ML, having satisfied structural stability, is a FM half-semiconducting electrene (La3+2H-⋅e-) with its magnetic moments localized at the lattice interstitial sites rather than La atoms. At the same time, LaH2ML holds the following desired attributes: a robust out-of-plane FM ground state with a highTC(334 K), a sizable valley polarization (166 meV), a wide energy window (137 meV) harboring clean single-valley carriers, and a direct bandgap. These results identify a much needed ideal ferrovalley semiconductor candidate, holding the promising application potential in valleytronics and spintronics devices.
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Affiliation(s)
- Yongting Shi
- School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, People's Republic of China
| | - Ningning Jia
- School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, People's Republic of China
| | - Jiangtao Cai
- Department of Physics, Shaanxi University of Science and Technology, Xi'an 710021, People's Republic of China
| | - Zhiheng Lyu
- School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, People's Republic of China
| | - Zhifeng Liu
- School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, People's Republic of China
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12
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Lin Z, Liu Y, Wang Z, Xu S, Chen S, Duan W, Monserrat B. Phonon-Limited Valley Polarization in Transition-Metal Dichalcogenides. PHYSICAL REVIEW LETTERS 2022; 129:027401. [PMID: 35867458 DOI: 10.1103/physrevlett.129.027401] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Accepted: 06/07/2022] [Indexed: 06/15/2023]
Abstract
The ability to selectively photoexcite at different Brillouin zone valleys forms the basis of valleytronics and other valley-related physics. Symmetry arguments combined with static lattice first-principles calculations suggest an ideal 100% valley polarization in transition-metal dichalcogenides under circularly polarized light. However, experimental reports of the valley polarization range from 32% to almost 100%. Possible explanations for this discrepancy include phonon-mediated transitions, which would place a fundamental limit to valley polarization, and defect-mediated transitions, which could, in principle, be reduced with cleaner samples. We explore the phonon-mediated fundamental limit by performing calculations of phonon-mediated optical absorption for circularly polarized light entirely from the first principles. We also use group theory to reveal the microscopic mechanisms behind the phonon-mediated excitations, discovering contributions from several individual phonon modes and from multiphonon processes. Overall, our calculations show that the phonon-limited valley polarization is around 70% at room temperature for state-of-the-art valleytronic materials including MoSe_{2}, MoS_{2}, WS_{2}, WSe_{2}, and MoTe_{2}. This fundamental limit implies that sufficiently pure transition-metal dichalcogenides are ideal candidates for valleytronics applications.
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Affiliation(s)
- Zuzhang Lin
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
- State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
- Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Yizhou Liu
- Department of Condensed Matter Physics, Weizmann Institute of Science, 7610001 Rehovot, Israel
| | - Zun Wang
- State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
| | - Shengnan Xu
- State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
| | - Siyu Chen
- Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Wenhui Duan
- Institute for Advanced Study, Tsinghua University, Beijing 100084, China
- State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
| | - Bartomeu Monserrat
- Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
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13
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Strain engineering of electronic properties and anomalous valley hall conductivity of transition metal dichalcogenide nanoribbons. Sci Rep 2022; 12:11285. [PMID: 35788139 PMCID: PMC9253103 DOI: 10.1038/s41598-022-13398-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Accepted: 05/24/2022] [Indexed: 12/02/2022] Open
Abstract
Strain engineering is a powerful technique for tuning electronic properties and valley degree of freedom in honeycomb structure of two-dimensional crystals. Carriers in + k and − k (opposite Berry curvature) in transition metal dichalcogenide (TMD) with broken inversion symmetry act as effective magnetic fields, where this polarized valleys are suitable for encoding information. In this work, we study the strained TMD nanoribbons by Slater-Koster tight-binding model, which acquires electronic bands in whole Brillouin zone. From this, we derive a generic profile of strain effect on the electronic band structure of TMD nanoribbons, which shows indirect band gap, and also exhibits a phase transition from semiconductor to metallic by applying uniaxial X-tensile and Y-arc type of strain. Midgap states in strained TMD nanoribbons are determined by calculation of localized density of electron states. Moreover, our findings of anomalous valley Hall conductivity reveal that the creation of pseudogauge fields using strained TMD nanoribbons affect the Dirac electrons, which generate the new quantized Landau level. Furthermore, we demonstrate in strained TMD nanoribbons that strain field can effectively tune both the magnitude and sign of valley Hall conductivity. Our work elucidates the valley Hall transport in strained TMDs due to pseudo-electric and pseudo-magnetic filed will be applicable as information carries for future electronics and valleytronics.
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14
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Lu J, Qu F, Zeng H, Cavalheiro Dias A, Bradão DS, Ren J. Intrinsic Valley Splitting and Direct-to-Indirect Band Gap Transition in Monolayer HfZrSiCO 2. J Phys Chem Lett 2022; 13:5204-5212. [PMID: 35666623 DOI: 10.1021/acs.jpclett.2c01090] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Both a reasonably large valley splitting (VS) and a sufficiently long valley exciton lifetime are crucial in valleytronics device applications. Currently, no single system possesses both attributes simultaneously. Herein, we demonstrate that a Janus monolayer HfZrSiCO2 concurrently hosts a giant intrinsic VS and excitonic quasi-particles with long valley lifetime due to valley-sublayer coupling and built-in electric field. In addition, the band structure of the monolayer HfZrSiCO2 can be continuously manipulated by either an external electric field or a biaxial strain, giving rise to a tunable VS and driving a direct-to-indirect band gap transition. Moreover, the system exhibits valley-contrasting linear dichroism in exciton absorption. These results suggest that the Janus monolayer HfZrSiCO2 is a promising candidate for information applications.
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Affiliation(s)
- Jiajun Lu
- School of Physics and Electronics, Shandong Normal University, Jinan 250014, China
| | - Fanyao Qu
- Instituto de Física, Universidade de Brasília, Brasília-DF 70919-970, Brazil
- International Center for Condensed Matter Physics, University of Brasília, 04513 Brasília-DF, Brazil
| | - Hao Zeng
- Department of Physics, University at Buffalo, the State University of New York, Buffalo, New York 14260, United States
| | - Alexandre Cavalheiro Dias
- Instituto de Física, Universidade de Brasília, Brasília-DF 70919-970, Brazil
- International Center for Condensed Matter Physics, University of Brasília, 04513 Brasília-DF, Brazil
| | - David S Bradão
- Instituto de Física, Universidade de Brasília, Brasília-DF 70919-970, Brazil
| | - Junfeng Ren
- School of Physics and Electronics, Shandong Normal University, Jinan 250014, China
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15
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Huang L, Zhu X, Hu G, Deng C, Sun Y, Wang D, Lu M, Yun B, Zhang R, Zhang Y, Cui Y. Electrical Switching of the Off-Resonance Room-Temperature Valley Polarization in Monolayer MoS 2 by a Double-Resonance Chiral Microstructure. ACS APPLIED MATERIALS & INTERFACES 2022; 14:22381-22388. [PMID: 35511437 DOI: 10.1021/acsami.2c03688] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Enhancing and expanding the manipulated range of room-temperature valley polarization at off-resonance wavelength is extremely crucial to developing various functional valleytronic devices. Although these have been realized through the double-resonance strategy or twist-angle engineering, the demand for electrical control over the concepts remains elusive. Here, we fabricate a gate-tunable double-resonance chiral microstructure using a molybdenum disulfides (MoS2) monolayer. On the basis of the varied interface charge density, we demonstrate the huge photoluminescence (PL) tuning ability of this configuration. Furthermore, benefiting predominately from the screening of long-range e-h exchange interactions and the chiral Purcell effect, the electrical switching of the room-temperature valley polarization at off-resonance wavelength is also realized. Our work enriches the functions of TMDs-based optoelectronic devices and may create important applications in future valley-polarized encode and information processing devices.
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Affiliation(s)
- Lei Huang
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Xiaofan Zhu
- Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing 211189, China
| | - Guohua Hu
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Chunyu Deng
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Yu Sun
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Dongyu Wang
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Mengjia Lu
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Binfeng Yun
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Ruohu Zhang
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
| | - Yan Zhang
- Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing 211189, China
| | - Yiping Cui
- Advanced Photonics Center, School of Electronic Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China
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16
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Fan J, Sun M. Transition Metal Dichalcogenides (TMDCs) Heterostructures: Synthesis, Excitons and Photoelectric Properties. CHEM REC 2022; 22:e202100313. [PMID: 35452180 DOI: 10.1002/tcr.202100313] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 03/22/2022] [Accepted: 04/11/2022] [Indexed: 11/06/2022]
Abstract
Transition metal dichalcogenides (TMDCs) have good flexibility, light absorption, and carrier mobility, and can be used to fabricate wearable devices and photodetectors. In addition, the band gaps of these materials are adjustable, which are related to the number of stacking layers. The the material properties can be changed by vertically stacking TMDCs to form van der Waals (vdW) heterostructures. Compared with single-layer TMDC, the vdW heterostructure has better light response and more efficient photoelectric conversion. Interlayer excitons formed in vdW heterostructure have a longer exciton lifetime and unique valley selectivity compared with intralayer excitons, which promotes the research on TMDCs materials in photoelectric field, valley electronics, carrier dynamics, etc. In this paper, the methods of synthesizing heterostructures are introduced. Photoelectric properties, valley dynamics, electronic properties and related applications of TMDCs vdW heterostructures are also discussed. Heterostructures stacked with different materials, stacking modes, and twist angles all can affect the properties. Hence, it brings more creativity and research direction to the material field.
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Affiliation(s)
- Jianuo Fan
- School of Mathematics and Physics, Beijing Advanced Innovation Center for Materials Genome Engineering, University of Science and Technology Beijing, Beijing, 100083, PR China
| | - Mengtao Sun
- School of Mathematics and Physics, Beijing Advanced Innovation Center for Materials Genome Engineering, University of Science and Technology Beijing, Beijing, 100083, PR China
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17
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Huang L, Krasnok A, Alú A, Yu Y, Neshev D, Miroshnichenko AE. Enhanced light-matter interaction in two-dimensional transition metal dichalcogenides. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2022; 85:046401. [PMID: 34939940 DOI: 10.1088/1361-6633/ac45f9] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Accepted: 12/16/2021] [Indexed: 05/27/2023]
Abstract
Two-dimensional (2D) transition metal dichalcogenide (TMDC) materials, such as MoS2, WS2, MoSe2, and WSe2, have received extensive attention in the past decade due to their extraordinary electronic, optical and thermal properties. They evolve from indirect bandgap semiconductors to direct bandgap semiconductors while their layer number is reduced from a few layers to a monolayer limit. Consequently, there is strong photoluminescence in a monolayer (1L) TMDC due to the large quantum yield. Moreover, such monolayer semiconductors have two other exciting properties: large binding energy of excitons and valley polarization. These properties make them become ideal materials for various electronic, photonic and optoelectronic devices. However, their performance is limited by the relatively weak light-matter interactions due to their atomically thin form factor. Resonant nanophotonic structures provide a viable way to address this issue and enhance light-matter interactions in 2D TMDCs. Here, we provide an overview of this research area, showcasing relevant applications, including exotic light emission, absorption and scattering features. We start by overviewing the concept of excitons in 1L-TMDC and the fundamental theory of cavity-enhanced emission, followed by a discussion on the recent progress of enhanced light emission, strong coupling and valleytronics. The atomically thin nature of 1L-TMDC enables a broad range of ways to tune its electric and optical properties. Thus, we continue by reviewing advances in TMDC-based tunable photonic devices. Next, we survey the recent progress in enhanced light absorption over narrow and broad bandwidths using 1L or few-layer TMDCs, and their applications for photovoltaics and photodetectors. We also review recent efforts of engineering light scattering, e.g., inducing Fano resonances, wavefront engineering in 1L or few-layer TMDCs by either integrating resonant structures, such as plasmonic/Mie resonant metasurfaces, or directly patterning monolayer/few layers TMDCs. We then overview the intriguing physical properties of different van der Waals heterostructures, and their applications in optoelectronic and photonic devices. Finally, we draw our opinion on potential opportunities and challenges in this rapidly developing field of research.
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Affiliation(s)
- Lujun Huang
- School of Engineering and Information Technology, University of New South Wales, Canberra, ACT, 2600, Australia
| | - Alex Krasnok
- Department of Electrical and Computer Engineering, Florida International University, Miami, FL 33174, United States of America
| | - Andrea Alú
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY 10031, United States of America
- Physics Program, Graduate Center, City University of New York, New York, NY 10016, United States of America
| | - Yiling Yu
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
| | - Dragomir Neshev
- ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), Department of Electronic Materials Engineering, Research School of Physics, The Australian National University, Canberra, ACT 2601, Australia
| | - Andrey E Miroshnichenko
- School of Engineering and Information Technology, University of New South Wales, Canberra, ACT, 2600, Australia
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18
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Chen PG, Li Z, Qi Y, Lo TW, Wang S, Jin W, Wong KY, Fan S, Zayats AV, Lei D. Long-Range Directional Routing and Spatial Selection of High-Spin-Purity Valley Trion Emission in Monolayer WS 2. ACS NANO 2021; 15:18163-18171. [PMID: 34730338 DOI: 10.1021/acsnano.1c06955] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Valley-dependent excitation and emission in transition metal dichalcogenides (TMDCs) have recently emerged as a new avenue for optical data manipulation, quantum optical technologies, and chiral photonics. The valley-polarized electronic states can be optically addressed through photonic spin-orbit interaction of excitonic emission, typically with plasmonic nanostructures, but their performance is limited by the low quantum yield of neutral excitons in TMDC multilayers and the large Ohmic loss of plasmonic systems. Here, we demonstrate a valleytronic system based on the trion emission in high-quantum-yield WS2 monolayers chirally coupled to a low-loss microfiber. The integrated system uses the spin properties of the waveguided modes to achieve long-range directional routing of valley excitations and also provides an approach to selectively address valley-dependent emission from different spatial locations around the microfiber. This valleytronic interface can be integrated with fiber communication devices, allowing for merging valley polarization and chiral photonics as an alternative mechanism for optical information transport and manipulation in classical and quantum regimes.
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Affiliation(s)
- Pei-Gang Chen
- Department of Materials Science and Engineering, The City University of Hong Kong, Hong Kong 999077, China
| | - Zhiyong Li
- State Key Laboratory of Chemical Biology and Drug Discovery, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong 999077, China
| | - Yun Qi
- Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong 999077, China
| | - Tsz Wing Lo
- Department of Materials Science and Engineering, The City University of Hong Kong, Hong Kong 999077, China
| | - Shubo Wang
- Department of Physics, City University of Hong Kong, Hong Kong 999077, China
| | - Wei Jin
- Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong 999077, China
| | - Kwok-Yin Wong
- State Key Laboratory of Chemical Biology and Drug Discovery, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong 999077, China
| | - Shanhui Fan
- Department of Electrical Engineering and Ginzton Laboratory, Stanford University, Stanford, California 94305-4088, United States
| | - Anatoly V Zayats
- Department of Physics and London Centre for Nanotechnology, King's College London, Strand, London WC2R 2LS, U.K
| | - Dangyuan Lei
- Department of Materials Science and Engineering, The City University of Hong Kong, Hong Kong 999077, China
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19
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Yin ZB, Chen XY, Wang YP, Long MQ. The magnetic proximity effect at the MoS 2/CrI 3interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 34:035002. [PMID: 34598164 DOI: 10.1088/1361-648x/ac2c3c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Accepted: 10/01/2021] [Indexed: 06/13/2023]
Abstract
The vicinity to a two-dimensional magnetic material provides a simple and effective way to break the valley degeneracy of transition-metal dichalcogenides because of the magnetic proximity effect. Based on first-principles calculations, we study the band structure of a MoS2/CrI3van der Waals heterostructure and its manipulation by vertical electric fields. A huge valley splitting of about 19.60 meV, equivalent to an external magnetic fields of about 89.0 T can be generated by an electric field of 0.115 V Å-1. The electric field causes discontinuous changes in the valley splitting. The electric field drives the bands of MoS2across those of CrI3. At the critical electric fields, the interlayer orbital hybridization leads to the energy level repulsion and an abrupt exchange of the band index. We also study the effect of interlayer distance on the valley splitting and observe a more significant electric field modulation. This work deepens our understanding on the interfacial magnetic proximity effect as a result of the orbital hybridization across the van der Waals gap.
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Affiliation(s)
- Zhi-Bo Yin
- School of Physics and Electronics, Hunan Key Laboratory for Super-Micro Structure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, People's Republic of China
| | - Xiao-Yan Chen
- School of Physics and Electronics, Hunan Key Laboratory for Super-Micro Structure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, People's Republic of China
| | - Yun-Peng Wang
- School of Physics and Electronics, Hunan Key Laboratory for Super-Micro Structure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, People's Republic of China
| | - Meng-Qiu Long
- School of Physics and Electronics, Hunan Key Laboratory for Super-Micro Structure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, People's Republic of China
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20
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Hossain MS, Ma MK, Villegas-Rosales KA, Chung YJ, Pfeiffer LN, West KW, Baldwin KW, Shayegan M. Spontaneous Valley Polarization of Itinerant Electrons. PHYSICAL REVIEW LETTERS 2021; 127:116601. [PMID: 34558923 DOI: 10.1103/physrevlett.127.116601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 07/28/2021] [Indexed: 06/13/2023]
Abstract
Memory or transistor devices based on an electron's spin rather than its charge degree of freedom offer certain distinct advantages and comprise a cornerstone of spintronics. Recent years have witnessed the emergence of a new field, valleytronics, which seeks to exploit an electron's valley index rather than its spin. An important component in this quest would be the ability to control the valley index in a convenient fashion. Here we show that the valley polarization can be switched from zero to 1 by a small reduction in density, simply tuned by a gate bias, in a two-dimensional electron system. This phenomenon, which is akin to Bloch spin ferromagnetism, arises fundamentally as a result of electron-electron interaction in an itinerant, dilute electron system. Essentially, the kinetic energy favors an equal distribution of electrons over the available valleys, whereas the interaction between electrons prefers single-valley occupancy below a critical density. The gate-bias-tuned transition we observe is accompanied by a sudden, twofold change in sample resistance, making the phenomenon of interest for potential valleytronic transistor device applications. Our observation constitutes a quintessential demonstration of valleytronics in a very simple experiment.
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Affiliation(s)
- Md S Hossain
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - M K Ma
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K A Villegas-Rosales
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Y J Chung
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - L N Pfeiffer
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W West
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W Baldwin
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - M Shayegan
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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21
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She XC, Zhang RL, Zhao JZ, Qi DX, Zou Y, Peng RW. Tunable valley polarization in Janus WSSe by magnetic proximity coupling to a CrI 3 layer. Phys Chem Chem Phys 2021; 23:18182-18188. [PMID: 34612281 DOI: 10.1039/d1cp02577e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We investigate the electronic properties and valley physics of Janus monolayer WSSe on a CrI3 substrate layer based on first-principles calculations. It is shown that the K and K' valley degeneracy can be lifted which leads to valley polarization (VP) in the WSSe due to the magnetic proximity coupling to a magnetic substrate. The magnitude of VP is highly sensitive to the interfacial electronic properties and can be tuned by varying the stacking configurations of the heterostructure. Interestingly, the direction of VP can be altered by manipulating the layer alignment without reversing the magnetism orientation of the magnetic substrate CrI3. We suggest that the hybridization between the bands of WSSe and the substrate plays an important role. Meanwhile, the charge distributions have been mapped out to uncover the microscopic origin of the direction variable VP. In addition, large VP can be achieved by adjusting the interlayer spacing. Our investigations may have potential applications in the design of valleytronic devices.
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Affiliation(s)
- X C She
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
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22
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Ai H, Liu D, Geng J, Wang S, Lo KH, Pan H. Theoretical evidence of the spin-valley coupling and valley polarization in two-dimensional MoSi 2X 4 (X = N, P, and As). Phys Chem Chem Phys 2021; 23:3144-3151. [PMID: 33496290 DOI: 10.1039/d0cp05926a] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Very recently, the centimeter-scale MoSi2N4 monolayer was synthesized experimentally and exhibited a semiconducting nature with high mobility (Hong et al., Science, 2020, 369, 670-674). Here, we show that MoSi2N4 and its analogues, MoSi2P4 and MoSi2As4, are potential two-dimensional (2D) materials for valleytronics based on first-principles calculations. We demonstrate that the intrinsic inversion symmetry breaking and strong spin-orbital coupling lead to the remarkable spin-valley coupling in the inequivalent valleys at K and K' points, which result in not only the valley-contrasting transport properties, but also the spin and valley coupled optical selection rules. Moreover, the in-plane strain can tune the bandgaps and spin splitting or even induce an indirect-to-direct bandgap transition for promising application in the strain-tunable valleytronics. We find that the valley polarization can be generated by doping magnetic element. Our findings offer theoretical insight into the exotic physical properties of novel MoSi2N4-family materials beyond transition metal dichalcogenides.
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Affiliation(s)
- Haoqiang Ai
- Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Macao SAR, 999078, P. R. China.
| | - Di Liu
- Institute of Applied Physics and Materials Engineering, University of Macau, Macao SAR, 999078, P. R. China.
| | - Jiazhong Geng
- Institute of Applied Physics and Materials Engineering, University of Macau, Macao SAR, 999078, P. R. China.
| | - Shuangpeng Wang
- Institute of Applied Physics and Materials Engineering, University of Macau, Macao SAR, 999078, P. R. China.
| | - Kin Ho Lo
- Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Macao SAR, 999078, P. R. China.
| | - Hui Pan
- Institute of Applied Physics and Materials Engineering, University of Macau, Macao SAR, 999078, P. R. China. and Department of Physics and Chemistry, Faculty of Science and Technology, University of Macau, Macao SAR, 999078, P. R. China
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23
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Wang Y, Wei W, Li F, Lv X, Huang B, Dai Y. Valley polarization caused by crystalline symmetry breaking. MATERIALS HORIZONS 2021; 8:244-249. [PMID: 34874021 DOI: 10.1039/d0mh01441a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In two-dimensional (2D) hexagonal lattices with inversion asymmetry, time-reversal (T) connected valleys are at the center of current valleytronic research. In order to trigger valley polarization, dynamical processes and/or magnetism have been considered. In this work, we propose a new mechanism, valley-contrasting sublattice polarization (VCSP), to polarize valleys by reducing the crystalline symmetry that connects the valleys. In our mechanism, significant valley polarization could be readily generated without magnetism, an electric field, or an optical process. Based on tight-binding model analysis and first-principle calculations, the control of valley polarization via crystalline symmetry can be successfully realized in concrete LaOBiS2 polytypes with Peierls-like structure distortion. Our results provide an unprecedented possibility for exploring valley-contrasting physics.
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Affiliation(s)
- Yuanyuan Wang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Wei Wei
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Fengping Li
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Xingshuai Lv
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Baibiao Huang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
| | - Ying Dai
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
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Suntornwipat N, Majdi S, Gabrysch M, Kovi KK, Djurberg V, Friel I, Twitchen DJ, Isberg J. A Valleytronic Diamond Transistor: Electrostatic Control of Valley Currents and Charge-State Manipulation of NV Centers. NANO LETTERS 2021; 21:868-874. [PMID: 33337898 PMCID: PMC7872423 DOI: 10.1021/acs.nanolett.0c04712] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Revised: 12/08/2020] [Indexed: 05/22/2023]
Abstract
The valley degree of freedom in many-valley semiconductors provides a new paradigm for storing and processing information in valleytronic and quantum-computing applications. Achieving practical devices requires all-electric control of long-lived valley-polarized states, without the use of strong external magnetic fields. Because of the extreme strength of the carbon-carbon bond, diamond possesses exceptionally stable valley states that provide a useful platform for valleytronic devices. Using ultrapure single-crystalline diamond, we demonstrate electrostatic control of valley currents in a dual-gate field-effect transistor, where the electrons are generated with a short ultraviolet pulse. The charge current and the valley current measured at the receiving electrodes are controlled separately by varying the gate voltages. We propose a model to interpret experimental data, based on drift-diffusion equations coupled through rate terms, with the rates computed by microscopic Monte Carlo simulations. As an application, we demonstrate valley-current charge-state modulation of nitrogen-vacancy centers.
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Affiliation(s)
- Nattakarn Suntornwipat
- Division
for Electricity, Department of Electrical Engineering, Uppsala University, Box 65, 751 03, Uppsala, Sweden
| | - Saman Majdi
- Division
for Electricity, Department of Electrical Engineering, Uppsala University, Box 65, 751 03, Uppsala, Sweden
| | - Markus Gabrysch
- Division
for Electricity, Department of Electrical Engineering, Uppsala University, Box 65, 751 03, Uppsala, Sweden
| | - Kiran Kumar Kovi
- Division
for Electricity, Department of Electrical Engineering, Uppsala University, Box 65, 751 03, Uppsala, Sweden
- Center
for Nanoscale Materials, Argonne National
Laboratory, Argonne, Illinois 60439, United
States
| | - Viktor Djurberg
- Division
for Electricity, Department of Electrical Engineering, Uppsala University, Box 65, 751 03, Uppsala, Sweden
| | - Ian Friel
- Global
Innovation Centre, Element Six, Fermi Ave, Harwell Oxford, Oxfordshire OX11 0QR, United Kingdom
| | - Daniel J. Twitchen
- Global
Innovation Centre, Element Six, Fermi Ave, Harwell Oxford, Oxfordshire OX11 0QR, United Kingdom
| | - Jan Isberg
- Division
for Electricity, Department of Electrical Engineering, Uppsala University, Box 65, 751 03, Uppsala, Sweden
- E-mail:
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25
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Valley interference and spin exchange at the atomic scale in silicon. Nat Commun 2020; 11:6124. [PMID: 33257680 PMCID: PMC7705737 DOI: 10.1038/s41467-020-19835-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 10/29/2020] [Indexed: 11/23/2022] Open
Abstract
Tunneling is a fundamental quantum process with no classical equivalent, which can compete with Coulomb interactions to give rise to complex phenomena. Phosphorus dopants in silicon can be placed with atomic precision to address the different regimes arising from this competition. However, they exploit wavefunctions relying on crystal band symmetries, which tunneling interactions are inherently sensitive to. Here we directly image lattice-aperiodic valley interference between coupled atoms in silicon using scanning tunneling microscopy. Our atomistic analysis unveils the role of envelope anisotropy, valley interference and dopant placement on the Heisenberg spin exchange interaction. We find that the exchange can become immune to valley interference by engineering in-plane dopant placement along specific crystallographic directions. A vacuum-like behaviour is recovered, where the exchange is maximised to the overlap between the donor orbitals, and pair-to-pair variations limited to a factor of less than 10 considering the accuracy in dopant positioning. This robustness remains over a large range of distances, from the strongly Coulomb interacting regime relevant for high-fidelity quantum computation to strongly coupled donor arrays of interest for quantum simulation in silicon. Coupled donor wavefunctions in silicon are spatially resolved to evidence valley interference processes. An atomic-scale understanding of the interplay between interference, envelope anisotropy and crystal symmetries unveils a placement strategy compatible with existing technology where the exchange is insensitive to interference.
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26
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Li J, Goryca M, Wilson NP, Stier AV, Xu X, Crooker SA. Spontaneous Valley Polarization of Interacting Carriers in a Monolayer Semiconductor. PHYSICAL REVIEW LETTERS 2020; 125:147602. [PMID: 33064502 DOI: 10.1103/physrevlett.125.147602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 09/09/2020] [Indexed: 06/11/2023]
Abstract
We report magnetoabsorption spectroscopy of gated WSe_{2} monolayers in high magnetic fields up to 60 T. When doped with a 2D Fermi sea of mobile holes, well-resolved sequences of optical transitions are observed in both σ^{±} circular polarizations, which unambiguously and separately indicate the number of filled Landau levels (LLs) in both K and K^{'} valleys. This reveals the interaction-enhanced valley Zeeman energy, which is found to be highly tunable with hole density p. We exploit this tunability to align the LLs in K and K^{'}, and find that the 2D hole gas becomes unstable against small changes in LL filling and can spontaneously valley polarize. These results cannot be understood within a single-particle picture, highlighting the importance of exchange interactions in determining the ground state of 2D carriers in monolayer semiconductors.
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Affiliation(s)
- J Li
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - M Goryca
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - N P Wilson
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - A V Stier
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - X Xu
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - S A Crooker
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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27
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Scuri G, Andersen TI, Zhou Y, Wild DS, Sung J, Gelly RJ, Bérubé D, Heo H, Shao L, Joe AY, Mier Valdivia AM, Taniguchi T, Watanabe K, Lončar M, Kim P, Lukin MD, Park H. Electrically Tunable Valley Dynamics in Twisted WSe_{2}/WSe_{2} Bilayers. PHYSICAL REVIEW LETTERS 2020; 124:217403. [PMID: 32530686 DOI: 10.1103/physrevlett.124.217403] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2019] [Accepted: 05/06/2020] [Indexed: 05/25/2023]
Abstract
The twist degree of freedom provides a powerful new tool for engineering the electrical and optical properties of van der Waals heterostructures. Here, we show that the twist angle can be used to control the spin-valley properties of transition metal dichalcogenide bilayers by changing the momentum alignment of the valleys in the two layers. Specifically, we observe that the interlayer excitons in twisted WSe_{2}/WSe_{2} bilayers exhibit a high (>60%) degree of circular polarization (DOCP) and long valley lifetimes (>40 ns) at zero electric and magnetic fields. The valley lifetime can be tuned by more than 3 orders of magnitude via electrostatic doping, enabling switching of the DOCP from ∼80% in the n-doped regime to <5% in the p-doped regime. These results open up new avenues for tunable chiral light-matter interactions, enabling novel device schemes that exploit the valley degree of freedom.
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Affiliation(s)
- Giovanni Scuri
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Trond I Andersen
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - You Zhou
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Dominik S Wild
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Jiho Sung
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Ryan J Gelly
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Damien Bérubé
- Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - Hoseok Heo
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Linbo Shao
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Andrew Y Joe
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Andrés M Mier Valdivia
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Marko Lončar
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Mikhail D Lukin
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Hongkun Park
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA
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28
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Yu ZM, Guan S, Sheng XL, Gao W, Yang SA. Valley-Layer Coupling: A New Design Principle for Valleytronics. PHYSICAL REVIEW LETTERS 2020; 124:037701. [PMID: 32031831 DOI: 10.1103/physrevlett.124.037701] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Indexed: 06/10/2023]
Abstract
The current valleytronics research is based on the paradigm of time-reversal-connected valleys in two-dimensional (2D) hexagonal materials, which forbids the fully electric generation of valley polarization by a gate field. Here, we go beyond the existing paradigm to explore 2D systems with a novel valley-layer coupling (VLC) mechanism, where the electronic states in the emergent valleys have a valley-contrasted layer polarization. The VLC enables a direct coupling between a valley and a gate electric field. We analyze the symmetry requirements for a system to host VLC, demonstrate our idea via first-principles calculations and model analysis of a concrete 2D material example, and show that an electric, continuous, wide-range, and switchable control of valley polarization can be achieved by VLC. Furthermore, we find that systems with VLC can exhibit other interesting physics, such as valley-contrasting linear dichroism and optical selection of the valley and the electric polarization of interlayer excitons. Our finding opens a new direction for valleytronics and 2D materials research.
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Affiliation(s)
- Zhi-Ming Yu
- Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems, and School of Physics, Beijing Institute of Technology, Beijing 100081, China
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
| | - Shan Guan
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | - Xian-Lei Sheng
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
- Department of Physics, Key Laboratory of Micro-nano Measurement-Manipulation and Physics (Ministry of Education), Beihang University, Beijing 100191, China
| | - Weibo Gao
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
- The Photonics Institute and Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371, Singapore
| | - Shengyuan A Yang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
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29
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Shi WB, He J, Li QX, She XC, Wang D, Jing H, Zhang RL, Zhao JZ, Peng RW, Xu H, Wang M. Asymmetric valley polarization and photoluminescence in MoS 2/MoO 3 heterostructure. OPTICS EXPRESS 2019; 27:38451-38462. [PMID: 31878612 DOI: 10.1364/oe.27.038451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 11/27/2019] [Indexed: 06/10/2023]
Abstract
We investigate circularly polarized photoluminescence (PL) in the MoS2/MoO3 heterostructure, which was fabricated by transferring MoS2 monolayer to cover the MoO3 few layers on the SiO2/Si substrate. It is shown that the PL with the same helicity as the excitation light is dominant due to the inherent chiral optical selectivity, which allows exciting one of the valleys in MoS2 monolayer. The degree of polarization (DP), which characterizes the intensity difference of two chiral components of PL, is unequal for the right-handed and left-handed circularly polarized excitations in the MoS2/MoO3 heterostructure. This effect is different from the one in pristine MoS2. Our Raman spectra results together with ab initio calculations indicate the p-doped features of the MoS2 when it covers the MoO3 layers. Thus the possible explanation of the unequal DP is that the p-doping process generates a built-in voltage and therefore brings the difference of electron-hole overlaps between K and K' valleys. Namely the asymmetric valley polarization may be obtained in the MoS2/MoO3 heterostructure. Consequently, the circularly polarized PL caused by the electron-hole recombination at K and K' valleys manifests unequal DP for the right-handed and left-handed helix excitations. This asymmetric effect is further enhanced by decreasing the temperature in the MoS2/MoO3 heterostructure. Our investigation provides a unique platform for developing novel two-dimensional valleytronic devices.
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30
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Huang K, Wang P, Pfeiffer LN, West KW, Baldwin KW, Liu Y, Lin X. Resymmetrizing Broken Symmetry with Hydraulic Pressure. PHYSICAL REVIEW LETTERS 2019; 123:206602. [PMID: 31809100 DOI: 10.1103/physrevlett.123.206602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Indexed: 06/10/2023]
Abstract
Recent progress in condensed matter physics, such as for graphene, topological insulators, and Weyl semimetals, often originate from the specific topological symmetries of their lattice structures. Quantum states with different degrees of freedom, e.g., spin, valley, layer, etc., arise from these symmetries, and the coherent superposition of these states form multiple energy subbands. The pseudospin, a concept analogous to the Dirac spinor matrices, is a successful description of such multisubband systems. When the electron-electron interaction dominates, many-body quantum phases arise. They usually have discrete pseudospin polarizations and exhibit sharp phase transitions at certain universal critical pseudospin energy splittings. In this Letter, we present our discovery of hydrostatic-pressure-induced degeneracy between the two lowest Landau levels. This degeneracy is evidenced by the pseudospin polarization transitions of the fragile correlated quantum liquid phases near the Landau level filling factor ν=3/2. Benefitting from the constant hole concentration and the sensitive nature of these transitions, we study the fine-tuning effect of the hydrostatic pressure at the order of 10 μeV, well beyond the meV-level state-of-the-art resolution of other techniques.
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Affiliation(s)
- Ke Huang
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Pengjie Wang
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - L N Pfeiffer
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W West
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W Baldwin
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Yang Liu
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Xi Lin
- International Center for Quantum Materials, Peking University, Beijing 100871, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
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31
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Kareekunnan A, Muruganathan M, Mizuta H. Electrically controlled valley states in bilayer graphene. NANOSCALE 2019; 11:14707-14711. [PMID: 31343652 DOI: 10.1039/c9nr03621k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Valley current, a stable, dissipationless current, originates due to the emergence of Berry curvature in inversion symmetry broken systems. Several theoretical predictions and experimental observations have explored layer symmetry breaking in AB-stacked bilayer graphene due to long-range Coulomb interactions between the electrons. However, none of the experimental studies conducted so far have observed valley current in unbiased bilayer graphene, which makes it vital to study the Berry curvature in unbiased bilayer graphene. In this study, we observed a non-zero Berry curvature with opposite values at K and K' valleys, validating the argumentation of the asymmetry persistent in unbiased bilayer graphene. The magnitude, as well as the polarity of the Berry curvature, is tunable with the application of an out-of-plane electric field. These results are especially important because they can lead to the realization of a valley valve, in which the carriers from the K and K' valleys can be regulated with a gate at the centre of a bilayer graphene nanoribbon.
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Affiliation(s)
- Afsal Kareekunnan
- School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, 923-1292, Japan.
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32
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Premasiri K, Gao XPA. Tuning spin-orbit coupling in 2D materials for spintronics: a topical review. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:193001. [PMID: 30726777 DOI: 10.1088/1361-648x/ab04c7] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Atomically-thin 2D materials have opened up new opportunities in the past decade in realizing novel electronic device concepts, owing to their unusual electronic properties. The recent progress made in the aspect of utilizing additional degrees of freedom of the electrons such as spin and valley suggests that 2D materials have a significant potential in replacing current electronic-charge-based semiconductor technology with spintronics and valleytronics. For spintronics, spin-orbit coupling plays a key role in manipulating the electrons' spin degree of freedom to encode and process information, and there are a host of recent studies exploring this facet of 2D materials. We review the recent advances in tuning spin-orbit coupling of 2D materials which are of notable importance to the progression of spintronics.
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Affiliation(s)
- Kasun Premasiri
- Department of Physics, Case Western Reserve University, 2076 Adelbert Road, Cleveland, OH 44106, United States of America
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33
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Goryca M, Wilson NP, Dey P, Xu X, Crooker SA. Detection of thermodynamic "valley noise" in monolayer semiconductors: Access to intrinsic valley relaxation time scales. SCIENCE ADVANCES 2019; 5:eaau4899. [PMID: 30838326 PMCID: PMC6397030 DOI: 10.1126/sciadv.aau4899] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 01/14/2019] [Indexed: 06/09/2023]
Abstract
Together with charge and spin, many novel two-dimensional materials also permit information to be encoded in an electron's valley degree of freedom-that is, in particular momentum states in the material's Brillouin zone. With a view toward valley-based (opto)electronic technologies, the intrinsic time scales of valley scattering are therefore of fundamental interest. Here, we demonstrate an entirely noise-based approach for exploring valley dynamics in monolayer transition-metal dichalcogenide semiconductors. Exploiting their valley-specific optical selection rules, we use optical Faraday rotation to passively detect the thermodynamic fluctuations of valley polarization in a Fermi sea of resident carriers. This spontaneous "valley noise" reveals narrow Lorentzian line shapes and, therefore, long exponentially-decaying intrinsic valley relaxation. Moreover, the noise signatures validate both the relaxation times and the spectral dependence of conventional (perturbative) pump-probe measurements. These results provide a viable route toward quantitative measurements of intrinsic valley dynamics, free from any external perturbation, pumping, or excitation.
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Affiliation(s)
- M. Goryca
- National High Magnetic Field Laboratory, Los Alamos, NM 87545, USA
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland
| | - N. P. Wilson
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - P. Dey
- National High Magnetic Field Laboratory, Los Alamos, NM 87545, USA
| | - X. Xu
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - S. A. Crooker
- National High Magnetic Field Laboratory, Los Alamos, NM 87545, USA
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34
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Ma X, Ai H, Gao H, Zhang X, Li W, Zhao M. Valley polarization and ferroelectricity in a two-dimensional GaAsC 6 monolayer. Phys Chem Chem Phys 2019; 21:3954-3959. [PMID: 30706913 DOI: 10.1039/c8cp07444e] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Valley polarization and ferroelectricity are the two basic concepts in electronic device applications. However, the coexistence of these two scenarios in one material has not been reported. Here, using first-principles calculations, we demonstrated that the two-dimensional GaAsC6 monolayer which is a hybrid structure of GaAs and graphene has a pair of inequivalent valleys with opposite Berry curvatures and an intrinsic out-of-plane spontaneous electric polarization. It also has a direct band gap of about 1.937 eV and a high carrier mobility of about 1.80 × 105 cm2 V-1 s-1, which are promising for electronic device applications. The integration of valley polarization and ferroelectricity in a single material offers a promising platform for the design of electronic devices.
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Affiliation(s)
- Xikui Ma
- School of Physics and State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong, China
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35
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Wu Z, Zhou BT, Cai X, Cheung P, Liu GB, Huang M, Lin J, Han T, An L, Wang Y, Xu S, Long G, Cheng C, Law KT, Zhang F, Wang N. Intrinsic valley Hall transport in atomically thin MoS 2. Nat Commun 2019; 10:611. [PMID: 30723283 PMCID: PMC6363770 DOI: 10.1038/s41467-019-08629-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2018] [Accepted: 01/23/2019] [Indexed: 11/25/2022] Open
Abstract
Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom in addition to charge and spin. In the absence of inversion symmetry, these systems were predicted to exhibit opposite Hall effects for electrons from different valleys. Such valley Hall effects have been achieved only by extrinsic means, such as substrate coupling, dual gating, and light illuminating. Here we report the first observation of intrinsic valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS2, evidenced by considerable nonlocal resistance that scales cubically with local resistance. Such a hallmark survives even at room temperature with a valley diffusion length at micron scale. By contrast, no valley Hall signal is observed in the centrosymmetric bilayer MoS2. Our work elucidates the topological origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics. Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom. Here, the authors observe room-temperature valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS2 by purely electronic means, whereas no valley signal is detected for centrosymmetric bilayer MoS2.
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Affiliation(s)
- Zefei Wu
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China.
| | - Benjamin T Zhou
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Xiangbin Cai
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Patrick Cheung
- Department of Physics, University of Texas at Dallas, Richardson, TX, 75080, USA
| | - Gui-Bin Liu
- School of Physics, Beijing Institute of Technology, 100081, Beijing, China
| | - Meizhen Huang
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Jiangxiazi Lin
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Tianyi Han
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Liheng An
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Yuanwei Wang
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Shuigang Xu
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Gen Long
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Chun Cheng
- Department of Materials Science and Engineering, Southern University of Science and Technology, 518055, Shenzhen, China
| | - Kam Tuen Law
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China
| | - Fan Zhang
- Department of Physics, University of Texas at Dallas, Richardson, TX, 75080, USA.
| | - Ning Wang
- Department of Physics and the Center for Quantum Materials, the Hong Kong University of Science and Technology, Hong Kong, China.
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36
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Ciarrocchi A, Unuchek D, Avsar A, Watanabe K, Taniguchi T, Kis A. Polarization switching and electrical control of interlayer excitons in two-dimensional van der Waals heterostructures. NATURE PHOTONICS 2019; 13:131-136. [PMID: 30886643 PMCID: PMC6420072 DOI: 10.1038/s41566-018-0325-y] [Citation(s) in RCA: 112] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Accepted: 11/15/2018] [Indexed: 05/22/2023]
Abstract
Long-lived interlayer excitons in van der Waals heterostructures based on transition metal dichalcogenides, together with unique spin-valley physics, make them promising for next-generation photonic and valleytronic devices. While the emission characteristics of interlayer excitons have been studied, efficient manipulation of their valley-state, a necessary requirement for information encoding, is still lacking. Here, we demonstrate comprehensive electrical control of interlayer excitons in a MoSe2/WSe2 heterostructure. Encapsulation of our well-aligned stack with hexagonal boron nitride (h-BN) allows us to resolve two separate narrow interlayer transitions with opposite helicities under circularly polarized excitation, either preserving or reversing the polarization of incoming light. By electrically controlling their relative intensities, we realize a polarization switch with tuneable emission intensity and wavelength. Finally, we demonstrate large Zeeman shifts of these two transitions upon application of an external magnetic field. These results are interpreted within the picture of moiré-induced brightening of forbidden optical transitions. The ability to control the polarization of interlayer excitons is a step forward towards the manipulation of the valley degree-of-freedom in realistic device applications.
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Affiliation(s)
- Alberto Ciarrocchi
- Electrical Engineering Institute, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Dmitrii Unuchek
- Electrical Engineering Institute, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Ahmet Avsar
- Electrical Engineering Institute, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Andras Kis
- Electrical Engineering Institute, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Correspondence should be addressed to: Andras Kis,
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37
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Hossain MS, Ma MK, Chung YJ, Pfeiffer LN, West KW, Baldwin KW, Shayegan M. Unconventional Anisotropic Even-Denominator Fractional Quantum Hall State in a System with Mass Anisotropy. PHYSICAL REVIEW LETTERS 2018; 121:256601. [PMID: 30608773 DOI: 10.1103/physrevlett.121.256601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Indexed: 06/09/2023]
Abstract
The fractional quantum Hall state (FQHS) observed at a half-filled Landau level in an interacting two-dimensional electron system (2DES) is among the most exotic states of matter as its quasiparticles are expected to be Majorana excitations with non-Abelian statistics. We demonstrate here the unexpected presence of such a state in a novel 2DES with a strong band-mass anisotropy. The FQHS we observe has unusual characteristics. While its Hall resistance is well quantized at low temperatures, it exhibits highly anisotropic in-plane transport resembling compressible stripe or nematic charge-density-wave phases. More striking, the anisotropy sets in suddenly below a critical temperature, suggesting a finite-temperature phase transition. Our observations highlight how anisotropy modifies the many-body phases of a 2DES, and should further fuel the discussion surrounding the enigmatic even-denominator FQHS.
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Affiliation(s)
- Md Shafayat Hossain
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Meng K Ma
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Y J Chung
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - L N Pfeiffer
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W West
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W Baldwin
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - M Shayegan
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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38
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Kłopotowski Ł, Czechowski N, Mitioglu AA, Backes C, Maude DK, Plochocka P. Long-lived photoluminescence polarization of localized excitons in liquid exfoliated monolayer enriched WS 2. NANOTECHNOLOGY 2018; 29:335703. [PMID: 29790860 DOI: 10.1088/1361-6528/aac73e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Monolayer transition metal dichalcogenides (TMDs) constitute a family of materials, in which coupled spin-valley physics can be explored and which could find applications in novel optoelectronic devices. However, before applications can be designed, a scalable method of monolayer extraction is required. Liquid phase exfoliation is a technique providing large quantities of the monolayer material, but the spin-valley properties of thus obtained TMDs are unknown. In this work, we employ steady-state and time-resolved photoluminescence (PL) to investigate the relaxation dynamics of localized excitons (LXs) in liquid exfoliated WS2. The results reveal that the circular polarization lifetime of the PL exceeds by at least an order of magnitude the PL lifetime. A rate equations model allows us to reproduce quantitatively the experimental data and to conclude that the observed large and long-lived PL polarization originates from efficient trapping of free excitons at localization sites hindering the intervalley relaxation. Furthermore, our results show that the depolarization process is inefficient for LXs. We discuss various mechanisms leading to this effect such as suppression of intervalley scattering of the LXs or inefficient spin relaxation of the holes.
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Affiliation(s)
- Ł Kłopotowski
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
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39
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Zhu Z, Fauqué B, Behnia K, Fuseya Y. Magnetoresistance and valley degree of freedom in bulk bismuth. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:313001. [PMID: 29939150 DOI: 10.1088/1361-648x/aaced7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In this paper, we first review fundamental aspects of magnetoresistance in multi-valley systems based on the semiclassical theory. Then we will review experimental evidence and theoretical understanding of magnetoresistance in an archetypal multi-valley system, where the electric conductivity is set by the sum of the contributions of different valleys. Bulk bismuth has three valleys with an extremely anisotropic effective mass. As a consequence the magnetoconductivity in each valley is extremely sensitive to the orientation of the magnetic field. Therefore, a rotating magnetic field plays the role of a valley valve tuning the contribution of each valley to the total conductivity. In addition to this simple semiclassical effect, other phenomena arise in the high-field limit as a consequence of an intricate Landau spectrum. In the vicinity of the quantum limit, the orientation of magnetic field significantly affects the distribution of carriers in each valley, namely, the valley polarization is induced by the magnetic field. Moreover, experiment has found that well beyond the quantum limit, one or two valleys become totally empty. This is the only case in condensed matter physics where a Fermi sea is completely dried up by a magnetic field without a metal-insulator transition. There have been two long-standing problems on bismuth near the quantum limit: the large anisotropic Zeeman splitting of holes, and the extra peaks in quantum oscillations, which cannot be assigned to any known Landau levels. These problems are solved by taking into account the interband effect due to the spin-orbit couplings for the former, and the contributions from the twinned crystal for the latter. Up to here, the whole spectrum can be interpreted within the one-particle theory. Finally, we will discuss transport and thermodynamic signatures of breaking of the valley symmetry in this system. By this term, we refer to the observed spontaneous loss of threefold symmetry at high magnetic field and low temperature. Its theoretical understanding is still missing. We will discuss possible explanations.
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Affiliation(s)
- Zengwei Zhu
- Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China
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40
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Mueed MA, Hossain MS, Jo I, Pfeiffer LN, West KW, Baldwin KW, Shayegan M. Realization of a Valley Superlattice. PHYSICAL REVIEW LETTERS 2018; 121:036802. [PMID: 30085799 DOI: 10.1103/physrevlett.121.036802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Indexed: 06/08/2023]
Abstract
In a number of widely studied materials, such as Si, AlAs, Bi, graphene, MoS_{2}, and many transition metal dichalcogenide monolayers, electrons acquire an additional, spinlike degree of freedom at the degenerate conduction band minima, also known as "valleys." External symmetry-breaking fields such as mechanical strain, or electric or magnetic fields, can tune the valley polarization of these materials, making them suitable candidates for "valleytronics." Here we study a quantum well of AlAs, where the two-dimensional electrons reside in two energetically degenerate valleys. By fabricating a strain-inducing grating on the sample surface, we engineer a spatial modulation of the electron population in different valleys, i.e., a "valley superlattice" in the quantum well plane. Our results establish a novel manipulation technique of the valley degree of freedom, paving the way to realizing a valley-selective layered structure in multivalley materials, with potential application in valleytronics.
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Affiliation(s)
- M A Mueed
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Md Shafayat Hossain
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - I Jo
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - L N Pfeiffer
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W West
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W Baldwin
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - M Shayegan
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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41
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Valley-Selective Response of Nanostructures Coupled to 2D Transition-Metal Dichalcogenides. APPLIED SCIENCES-BASEL 2018. [DOI: 10.3390/app8071157] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Monolayer (1L) transition-metal dichalcogenides (TMDCs) are attractive materials for several optoelectronic applications because of their strong excitonic resonances and valley-selective response. Valley excitons in 1L-TMDCs are formed at opposite points of the Brillouin zone boundary, giving rise to a valley degree of freedom that can be treated as a pseudospin, and may be used as a platform for information transport and processing. However, short valley depolarization times and relatively short exciton lifetimes at room temperature prevent using valley pseudospins in on-chip integrated valley devices. Recently, it was demonstrated how coupling these materials to optical nanoantennas and metasurfaces can overcome this obstacle. Here, we review the state-of-the-art advances in valley-selective directional emission and exciton sorting in 1L-TMDC mediated by nanostructures and nanoantennas. We briefly discuss the optical properties of 1L-TMDCs paying special attention to their photoluminescence/absorption spectra, dynamics of valley depolarization, and the valley Hall effect. Then, we review recent works on nanostructures for valley-selective directional emission from 1L-TMDCs.
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42
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Miyauchi Y, Konabe S, Wang F, Zhang W, Hwang A, Hasegawa Y, Zhou L, Mouri S, Toh M, Eda G, Matsuda K. Evidence for line width and carrier screening effects on excitonic valley relaxation in 2D semiconductors. Nat Commun 2018; 9:2598. [PMID: 29968719 PMCID: PMC6030139 DOI: 10.1038/s41467-018-04988-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Accepted: 04/17/2018] [Indexed: 11/09/2022] Open
Abstract
Monolayers of transition metal dichalcogenides (TMDC) have recently emerged as excellent platforms for exploiting new physics and applications relying on electronic valley degrees of freedom in two-dimensional (2D) systems. Here, we demonstrate that Coulomb screening by 2D carriers plays a critical role in excitonic valley pseudospin relaxation processes in naturally carrier-doped WSe2 monolayers (1L-WSe2). The exciton valley relaxation times were examined using polarization- and time-resolved photoluminescence spectroscopy at temperatures ranging from 10 to 160 K. We show that the temperature-dependent exciton valley relaxation times in 1L-WSe2 under various exciton and carrier densities can be understood using a unified framework of intervalley exciton scattering via momentum-dependent long-range electron-hole exchange interactions screened by 2D carriers that depend on the carrier density and the exciton linewidth. Moreover, the developed framework was successfully applied to engineer the valley polarization of excitons in 1L-WSe2. These findings may facilitate the development of TMDC-based opto-valleytronic devices.
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Affiliation(s)
- Yuhei Miyauchi
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011, Japan. .,Graduate School of Science, Nagoya University, Chikusa, Nagoya, 464-8602, Japan.
| | - Satoru Konabe
- Research Institute for Science and Technology, Tokyo University of Science, 6-3-1 Katsushika-ku, Tokyo, 125-8585, Japan.,Department of Chemical Science and Technology, Hosei University, Koganei, Tokyo, 184-8584, Japan
| | - Feijiu Wang
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011, Japan.,Graduate School of Science, Nagoya University, Chikusa, Nagoya, 464-8602, Japan
| | - Wenjin Zhang
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011, Japan
| | - Alexander Hwang
- Department of Electrical and Computer Engineering, Rice University, Houston, TX, 77005, USA.,Department of Physics, Rice University, Houston, TX, 77005, USA
| | - Yusuke Hasegawa
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011, Japan
| | - Lizhong Zhou
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011, Japan
| | - Shinichiro Mouri
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011, Japan.,Department of Electrical and Electronic Engineering, Ritsumeikan University, Kusatsu, 525-8577, Japan
| | - Minglin Toh
- Department of Physics, National University of Singapore, Singapore, 117551, Singapore
| | - Goki Eda
- Department of Physics, National University of Singapore, Singapore, 117551, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore.,Department of Chemistry, National University of Singapore, Singapore, 117543, Singapore
| | - Kazunari Matsuda
- Institute of Advanced Energy, Kyoto University, Uji, Kyoto, 611-0011, Japan
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43
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Wang M, Ye L, Christensen J, Liu Z. Valley Physics in Non-Hermitian Artificial Acoustic Boron Nitride. PHYSICAL REVIEW LETTERS 2018; 120:246601. [PMID: 29957004 DOI: 10.1103/physrevlett.120.246601] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Indexed: 06/08/2023]
Abstract
The valley can serve as a new degree of freedom in the manipulation of particles or waves in condensed matter physics, whereas systems containing combinations of gain and loss elements constitute rich building units that can mimic non-Hermitian properties. By introducing gain and loss in artificial acoustic boron nitride, we show that the acoustic valley states and the valley-projected edge states display exotic behaviors in that they sustain either attenuated or amplified wave propagation. Our findings show how non-Hermiticity introduces a mechanism in tuning topological protected valley transports, which may have significance in advanced wave control for sensing and communication applications.
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Affiliation(s)
- Mudi Wang
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Liping Ye
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - J Christensen
- Department of Physics, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28916 Leganes (Madrid), Spain
| | - Zhengyou Liu
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
- Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
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44
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Diware MS, Ganorkar SP, Park K, Chegal W, Cho HM, Cho YJ, Kim YD, Kim H. Dielectric function, critical points, and Rydberg exciton series of WSe 2 monolayer. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:235701. [PMID: 29714172 DOI: 10.1088/1361-648x/aac187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The complex dielectric function ([Formula: see text]) of WSe2 monolayer grown by atomic layer deposition is investigated using spectroscopic ellipsometry. Band structure parameters are obtained by standard line-shape analysis of the second-energy-derivative of [Formula: see text] spectra. The fundamental band gap is observed at 2.26 eV, corresponds to transition between valence band (VB) maximum at the K point and conduction band (CB) minimum at Q point in the Brillouin zone (BZ). Two strong so-called A and B excitonic peaks in [Formula: see text] spectra originate from vertical transitions from spin-orbit split (0.43 eV) VB to CB at K point of the BZ. Binding energies of A and B exactions are 0.71 and 0.28 eV, respectively. Well resolved five excited excitons states has been detected within the spectral region between A and B. Energy profile of the Rydberg series shows significant deviation from the hydrogenic behavior, discussed in connection with the 2D hydrogen model. Results presented here will improve our understanding about the optical response of 2D materials and will help to design better optoelectronic applications and validate theoretical considerations.
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Affiliation(s)
- M S Diware
- CeNSCMR and Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
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45
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Lin S, Carvalho A, Yan S, Li R, Kim S, Rodin A, Carvalho L, Chan EM, Wang X, Castro Neto AH, Yao J. Accessing valley degree of freedom in bulk Tin(II) sulfide at room temperature. Nat Commun 2018; 9:1455. [PMID: 29654301 PMCID: PMC5899090 DOI: 10.1038/s41467-018-03897-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Accepted: 03/21/2018] [Indexed: 11/09/2022] Open
Abstract
The field of valleytronics has promised greater control of electronic and spintronic systems with an additional valley degree of freedom. However, conventional and two-dimensional valleytronic systems pose practical challenges in the utilization of this valley degree of freedom. Here we show experimental evidences of the valley effect in a bulk, ambient, and bias-free model system of Tin(II) sulfide. We elucidate the direct access and identification of different sets of valleys, based primarily on the selectivity in absorption and emission of linearly polarized light by optical reflection/transmission and photoluminescence measurements, and demonstrate strong optical dichroic anisotropy of up to 600% and nominal polarization degrees of up to 96% for the two valleys with band-gap values 1.28 and 1.48 eV, respectively; the ease of valley selection further manifested in their non-degenerate nature. Such discovery enables a new platform for better access and control of valley polarization. Valleytronics leverages the valley degree of freedom to engineer light-matter interaction. Here, the authors demonstrate a room temperature, bias-free valley effect in bulk SnS by means of spectroscopic measurements, previously unattainable using atomically thin transition metal dichalcogenides.
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Affiliation(s)
- Shuren Lin
- Department of Materials Science and Engineering, University of California, Berkeley, CA, 94720, USA.,The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Shancheng Yan
- School of Geography and Biological Information, Nanjing University of Posts and Telecommunications, 210023, Nanjing, People's Republic of China
| | - Roger Li
- Department of Materials Science and Engineering, University of California, Berkeley, CA, 94720, USA
| | - Sujung Kim
- Department of Materials Science and Engineering, University of California, Berkeley, CA, 94720, USA
| | - Aleksandr Rodin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Lídia Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Emory M Chan
- The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Xi Wang
- Department of Materials Science and Engineering, University of California, Berkeley, CA, 94720, USA
| | - Antonio H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Jie Yao
- Department of Materials Science and Engineering, University of California, Berkeley, CA, 94720, USA. .,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
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46
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Topological Valley Transport in Two-dimensional Honeycomb Photonic Crystals. Sci Rep 2018; 8:1588. [PMID: 29371636 PMCID: PMC5785496 DOI: 10.1038/s41598-018-20001-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 01/10/2018] [Indexed: 11/20/2022] Open
Abstract
Two-dimensional photonic crystals, in analogy to AB/BA stacking bilayer graphene in electronic system, are studied. Inequivalent valleys in the momentum space for photons can be manipulated by simply engineering diameters of cylinders in a honeycomb lattice. The inequivalent valleys in photonic crystal are selectively excited by a designed optical chiral source and bulk valley polarizations are visualized. Unidirectional valley interface states are proved to exist on a domain wall connecting two photonic crystals with different valley Chern numbers. With the similar optical vortex index, interface states can couple with bulk valley polarizations and thus valley filter and valley coupler can be designed. Our simple dielectric PC scheme can help to exploit the valley degree of freedom for future optical devices.
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47
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Dey P, Yang L, Robert C, Wang G, Urbaszek B, Marie X, Crooker SA. Gate-Controlled Spin-Valley Locking of Resident Carriers in WSe_{2} Monolayers. PHYSICAL REVIEW LETTERS 2017; 119:137401. [PMID: 29341682 DOI: 10.1103/physrevlett.119.137401] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Indexed: 05/22/2023]
Abstract
Using time-resolved Kerr rotation, we measure the spin-valley dynamics of resident electrons and holes in single charge-tunable monolayers of the archetypal transition-metal dichalcogenide (TMD) semiconductor WSe_{2}. In the n-type regime, we observe long (∼130 ns) polarization relaxation of electrons that is sensitive to in-plane magnetic fields B_{y}, indicating spin relaxation. In marked contrast, extraordinarily long (∼2 μs) polarization relaxation of holes is revealed in the p-type regime, which is unaffected by B_{y}, directly confirming long-standing expectations of strong spin-valley locking of holes in the valence band of monolayer TMDs. Supported by continuous-wave Kerr spectroscopy and Hanle measurements, these studies provide a unified picture of carrier polarization dynamics in monolayer TMDs, which can guide design principles for future valleytronic devices.
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Affiliation(s)
- P Dey
- National High Magnetic Field Laboratory, Los Alamos National Lab, Los Alamos, New Mexico 87545, USA
| | - Luyi Yang
- National High Magnetic Field Laboratory, Los Alamos National Lab, Los Alamos, New Mexico 87545, USA
| | - C Robert
- Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue Rangueil, 31077 Toulouse, France
| | - G Wang
- Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue Rangueil, 31077 Toulouse, France
| | - B Urbaszek
- Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue Rangueil, 31077 Toulouse, France
| | - X Marie
- Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue Rangueil, 31077 Toulouse, France
| | - S A Crooker
- National High Magnetic Field Laboratory, Los Alamos National Lab, Los Alamos, New Mexico 87545, USA
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48
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An XT, Xiao J, Tu MWY, Yu H, Fal'ko VI, Yao W. Realization of Valley and Spin Pumps by Scattering at Nonmagnetic Disorders. PHYSICAL REVIEW LETTERS 2017; 118:096602. [PMID: 28306268 DOI: 10.1103/physrevlett.118.096602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2016] [Indexed: 06/06/2023]
Abstract
The recent success in optical pumping of valley polarization in two-dimensional transition metal dichalcogenides (TMDs) has greatly promoted the concept of valley-based informatics and electronics. However, between the demonstrated valley polarization of transient electron-hole pair excitations and practical valleytronic operations, there exist obvious gaps to fill, among which is the valley pump of long-lived charge carriers. Here we discover that the quested valley pump of electrons or holes can be realized simply by scattering at the ubiquitous nonmagnetic disorders, not relying on any specific material property. The mechanism is rooted in the nature of the valley as a momentum space index: the intervalley backscattering in general has a valley contrasted rate due to the distinct momentum transfers, causing a net transfer of population from one valley to another. As examples, we numerically demonstrate the sizable valley pump effects driven by charge current in nanoribbons of monolayer TMDs, where the spin-orbit scattering by nonmagnetic disorders also realizes a spin pump for the spin-valley locked holes. Our finding points to a new opportunity towards valley spintronics, turning disorders from a deleterious factor to a resource of valley and spin polarization.
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Affiliation(s)
- Xing-Tao An
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
- School of Science, Hebei University of Science and Technology, Shijiazhuang, Hebei 050018, China
| | - Jiang Xiao
- Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
- Institute for Nanoelectronics Devices and Quantum Computing, Fudan University, Shanghai 200433, China
| | - M W-Y Tu
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - Hongyi Yu
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - Vladimir I Fal'ko
- National Graphene Institute, University of Manchester, Booth St E, Manchester M13 9PL, United Kingdom
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
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49
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Wang Z, Shan J, Mak KF. Valley- and spin-polarized Landau levels in monolayer WSe 2. NATURE NANOTECHNOLOGY 2017; 12:144-149. [PMID: 27798606 DOI: 10.1038/nnano.2016.213] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2016] [Accepted: 09/12/2016] [Indexed: 06/06/2023]
Abstract
Electrons in monolayer transition metal dichalcogenides are characterized by valley and spin quantum degrees of freedom, making it possible to explore new physical phenomena and to foresee novel applications in the fields of electronics and optoelectronics. Theoretical proposals further suggest that Berry curvature effects, together with strong spin-orbit interactions, can generate unconventional Landau levels (LLs) under a perpendicular magnetic field. In particular, these would support valley- and spin-polarized chiral edge states in the quantum Hall regime. However, this unique LL structure has not been observed experimentally in transition metal dichalcogenides. Here we report the observation of fully valley- and spin-polarized LLs in high-quality WSe2 monolayers achieved by exploiting a van der Waals heterostructure device platform. We applied handedness-resolved optical reflection spectroscopy to probe the inter-LL transitions at individual valleys and derived the LL structure in turn. We also measured a sizeable doping-induced mass renormalization driven by the strong Coulomb interactions.
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Affiliation(s)
- Zefang Wang
- Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Jie Shan
- Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
| | - Kin Fai Mak
- Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
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Zhong L, Chen X, Qi J. Controlling the spin and valley degeneracy splitting in monolayer MnPSe3 by atom doping. Phys Chem Chem Phys 2017; 19:15388-15393. [DOI: 10.1039/c7cp00964j] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Monolayer manganese chalcogenophosphates MnPSe3 possess a pair of non-degenerate energy valleys in the vicinities of the vertices of the hexagonal Brillouin zone, which exhibit fascinating optical valley polarization.
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Affiliation(s)
- Liangshuai Zhong
- School of Physics and Electronic Engineering
- Jiangsu Normal University
- Xuzhou 221116
- People's Republic of China
| | - Xiaofang Chen
- School of Physics and Electronic Engineering
- Jiangsu Normal University
- Xuzhou 221116
- People's Republic of China
| | - Jingshan Qi
- School of Physics and Electronic Engineering
- Jiangsu Normal University
- Xuzhou 221116
- People's Republic of China
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