1
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Jiao R, Wei Q, Zhang L, Xie Y, He J, Zhou Y, Shen L, Yuan J. Enhancement and modulation of valley polarization in Janus CrSSe with internal and external electric fields. Phys Chem Chem Phys 2024; 26:13087-13093. [PMID: 38628113 DOI: 10.1039/d3cp05298b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2024]
Abstract
The valley polarization, induced by the magnetic proximity effect, in monolayer transition metal dichalcogenides (TMDCs), has attracted significant attention due to the intriguing fundamental physics. However, the enhancement and modulation of valley polarization for real device applications is still a challenge. Here, using first-principles calculations we investigate the valley polarization properties of monolayer TMDCs CrS2 and CrSe2 and how to enhance the valley polarization by constructing Janus CrSSe (with an internal electric field) and modulate the polarization in CrSSe by applying external electric fields. Janus CrSSe exhibits inversion symmetry breaking, internal electric field, spin-orbit coupling, and compelling spin-valley coupling. A magnetic substrate of the MnO2 monolayer can induce a modest magnetic moment in CrSe2, CrSe2, and CrSSe. Notably, the Janus structure with an internal electric field has a much larger valley p compared with its non-Janus counterparts. Moreover, the strength of valley polarization can be further modulated by applying external electric fields. These findings suggest that Janus materials hold promise for designing and developing advanced valleytronic devices.
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Affiliation(s)
- Runxian Jiao
- School of Physics and Electronic Engineering, Jiangsu University, Zhenjiang 212013, China
| | - Qingyuan Wei
- School of Physics and Electronic Engineering, Jiangsu University, Zhenjiang 212013, China
| | - Lichuan Zhang
- School of Physics and Electronic Engineering, Jiangsu University, Zhenjiang 212013, China
| | - Yuee Xie
- School of Physics and Electronic Engineering, Jiangsu University, Zhenjiang 212013, China
| | - Jingjing He
- College of Information Science and Technology, Nanjing Forestry University, Nanjing 210037, China.
| | - Yangbo Zhou
- School of Physics and Materials Science, Nanchang University, Nanchang 330031, China.
| | - Lei Shen
- Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117542, Singapore
| | - Jiaren Yuan
- School of Physics and Materials Science, Nanchang University, Nanchang 330031, China.
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2
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Hu Z, Wang H, Wang L, Wang H. A new charge transfer pathway in the MoSe 2-WSe 2 heterostructure under the conditions of B-excitons being resonantly pumped. Phys Chem Chem Phys 2024; 26:9424-9431. [PMID: 38446138 DOI: 10.1039/d3cp05282f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
Most transition metal dichalcogenide (TMD) heterostructures (HSs) exhibit a type II band alignment, leading to a charge transfer process accompanied by the transfer of spin-valley polarization and spontaneous formation of interlayer excitons. This unique band structure facilitates achieving a longer exciton lifetime and extended spin-valley polarization lifetime. However, the mechanism of charge transfer in type II TMD HSs is not fully comprehended. Here, the ultrafast charge transfer process is studied in MoSe2-WSe2 HS via valley-solved broadband pump-probe spectroscopy. Under the conditions of B-excitons of WSe2 and MoSe2 being resonantly pumped, a new charge transfer pathway through the higher energy state associated with the B-exciton is found. Meanwhile, the holes (electrons) in the WSe2 (MoSe2) layer of MoSe2-WSe2 HS produce obvious spin-valley polarization even under the condition of B-exciton of WSe2 (MoSe2) being resonantly pumped, and the lifetime can reach tens of ps, which is in stark contrast to the absence of A-exciton spin-valley polarization in monolayer WSe2 (MoSe2) under the same pumping condition. The results deepen the insight into the charge transfer process in type II TMD HSs and show the great potential of TMD HSs in the application of spin-valley electronics devices.
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Affiliation(s)
- Zifan Hu
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China.
| | - Hai Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China.
| | - Lei Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China.
| | - Haiyu Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China.
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3
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Hudson RJ, MacDonald TSC, Cole JH, Schmidt TW, Smith TA, McCamey DR. A framework for multiexcitonic logic. Nat Rev Chem 2024:10.1038/s41570-023-00566-y. [PMID: 38273177 DOI: 10.1038/s41570-023-00566-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/22/2023] [Indexed: 01/27/2024]
Abstract
Exciton science sits at the intersection of chemical, optical and spin-based implementations of information processing, but using excitons to conduct logical operations remains relatively unexplored. Excitons encoding information could be read optically (photoexcitation-photoemission) or electrically (charge recombination-separation), travel through materials via exciton energy transfer, and interact with one another in stimuli-responsive molecular excitonic devices. Excitonic logic offers the potential to mediate electrical, optical and chemical information. Additionally, high-spin triplet and quintet (multi)excitons offer access to well defined spin states of relevance to magnetic field effects, classical spintronics and spin-based quantum information science. In this Roadmap, we propose a framework for developing excitonic computing based on singlet fission (SF) and triplet-triplet annihilation (TTA). Various molecular components capable of modulating SF/TTA for logical operations are suggested, including molecular photo-switching and multi-colour photoexcitation. We then outline a pathway for constructing excitonic logic devices, considering aspects of circuit assembly, logical operation synchronization, and exciton transport and amplification. Promising future directions and challenges are identified, and the potential for realizing excitonic computing in the near future is discussed.
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Affiliation(s)
- Rohan J Hudson
- School of Chemistry, University of Melbourne, Melbourne, Victoria, Australia
- Australian Research Council Centre of Excellence in Exciton Science
| | - Thomas S C MacDonald
- Australian Research Council Centre of Excellence in Exciton Science
- School of Physics, UNSW Sydney, Sydney, New South Wales, Australia
| | - Jared H Cole
- Australian Research Council Centre of Excellence in Exciton Science
- School of Science, RMIT University, Melbourne, Victoria, Australia
| | - Timothy W Schmidt
- Australian Research Council Centre of Excellence in Exciton Science
- School of Chemistry, UNSW Sydney, Sydney, New South Wales, Australia
| | - Trevor A Smith
- School of Chemistry, University of Melbourne, Melbourne, Victoria, Australia
- Australian Research Council Centre of Excellence in Exciton Science
| | - Dane R McCamey
- Australian Research Council Centre of Excellence in Exciton Science, .
- School of Physics, UNSW Sydney, Sydney, New South Wales, Australia.
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4
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Zhang Y, Wang Y, Dai Y, Bai X, Hu X, Du L, Hu H, Yang X, Li D, Dai Q, Hasan T, Sun Z. Chirality logic gates. SCIENCE ADVANCES 2022; 8:eabq8246. [PMID: 36490340 PMCID: PMC9733934 DOI: 10.1126/sciadv.abq8246] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 10/31/2022] [Indexed: 06/17/2023]
Abstract
The ever-growing demand for faster and more efficient data transfer and processing has brought optical computation strategies to the forefront of research in next-generation computing. Here, we report a universal computing approach with the chirality degree of freedom. By exploiting the crystal symmetry-enabled well-known chiral selection rules, we demonstrate the viability of the concept in bulk silica crystals and atomically thin semiconductors and create ultrafast (<100-fs) all-optical chirality logic gates (XNOR, NOR, AND, XOR, OR, and NAND) and a half adder. We also validate the unique advantages of chirality gates by realizing multiple gates with simultaneous operation in a single device and electrical control. Our first demonstrations of logic gates using chiral selection rules suggest that optical chirality could provide a powerful degree of freedom for future optical computing.
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Affiliation(s)
- Yi Zhang
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
- QTF Centre of Excellence, Department of Applied Physics, Aalto University, Espoo 02150, Finland
| | - Yadong Wang
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
| | - Yunyun Dai
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
| | - Xueyin Bai
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
| | - Xuerong Hu
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
- Institute of Photonics and Photon Technology, Northwest University, Xi’an 710069, China
| | - Luojun Du
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
| | - Hai Hu
- CAS Key Laboratory of Nanophotonic Materials and Devices, National Center for Nanoscience and Technology, Beijing 100190, China
| | - Xiaoxia Yang
- CAS Key Laboratory of Nanophotonic Materials and Devices, National Center for Nanoscience and Technology, Beijing 100190, China
| | - Diao Li
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
| | - Qing Dai
- CAS Key Laboratory of Nanophotonic Materials and Devices, National Center for Nanoscience and Technology, Beijing 100190, China
| | - Tawfique Hasan
- Cambridge Graphene Centre, University of Cambridge, Cambridge CB3 0FA, UK
| | - Zhipei Sun
- Department of Electronics and Nanoengineering, Aalto University, Espoo 02150, Finland
- QTF Centre of Excellence, Department of Applied Physics, Aalto University, Espoo 02150, Finland
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5
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Zheng SW, Wang D, Wang HY, Wang H, Chen X, Zhao LY, Wang L, Li XB, Sun HB. Spin-Valley Depolarization in van der Waals Heterostructures. J Phys Chem Lett 2022; 13:5501-5507. [PMID: 35695739 DOI: 10.1021/acs.jpclett.2c01414] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The appearance of van der Waals heterostructures offers a new solution to valleytronics. Here, we observe the spin-valley depolarization process of electrons and holes in type-II MoS2-WSe2 heterostructures simultaneously for the first time by valley-resolved broad-band femtosecond pump-probe experiments. The different depolarization paths between electrons and holes make them have different spin-valley polarization lifetimes. The spin-valley depolarization pathway of holes is mainly dominated by a phonon-assisted intervalley scattering process, while intra- and intervalley coupling can trigger additional depolarization pathways for electrons. The hole polarization lifetime can be further prolonged to more than three times in trilayer heterostructure 2MoS2-WSe2. For MoS2-WS2 that has strong orbital hybridization of Mo and W atoms, both electrons and holes lose the spin-valley polarization extremely soon after charge separation, behaving similarly to intraexcitons in a monolayer. Our work advances the basic understanding of spin-valley depolarization of van der Waals heterostructures and facilitates the effort toward longer lifetime valleytronic devices for information transfer and storage applications.
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Affiliation(s)
- Shu-Wen Zheng
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Dan Wang
- Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, United States
| | - Hai-Yu Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Hai Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Xin Chen
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Le-Yi Zhao
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Lei Wang
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Xian-Bin Li
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
| | - Hong-Bo Sun
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Haidian, Beijing 100084, China
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6
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Katsch F, Selig M, Knorr A. Exciton-Scattering-Induced Dephasing in Two-Dimensional Semiconductors. PHYSICAL REVIEW LETTERS 2020; 124:257402. [PMID: 32639791 DOI: 10.1103/physrevlett.124.257402] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 01/25/2020] [Accepted: 06/01/2020] [Indexed: 05/13/2023]
Abstract
Enhanced Coulomb interactions in monolayer transition metal dichalcogenides cause tightly bound electron-hole pairs (excitons) that dominate their linear and nonlinear optical response. The latter includes bleaching, energy renormalizations, and higher-order Coulomb correlation effects like biexcitons and excitation-induced dephasing. While the first three are extensively studied, no theoretical footing for excitation-induced dephasing in exciton-dominated semiconductors is available so far. In this Letter, we present microscopic calculations based on excitonic Heisenberg equations of motion and identify the coupling of optically pumped excitons to exciton-exciton scattering continua as the leading mechanism responsible for an optical-power-dependent linewidth broadening (excitation-induced dephasing) and sideband formation. Performing time-, momentum-, and energy-resolved simulations, we quantitatively evaluate the exciton-induced dephasing for the most common monolayer transition metal dichalcogenides and find an excellent agreement with recent experiments.
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Affiliation(s)
- Florian Katsch
- Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Malte Selig
- Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
| | - Andreas Knorr
- Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany
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7
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He X, Chebl M, Yang DS. Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS 2. NANO LETTERS 2020; 20:2026-2033. [PMID: 32031381 DOI: 10.1021/acs.nanolett.9b05344] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
In this Letter, the ultrafast structural, interfacial, and carrier dynamics of monolayer MoS2 supported on sapphire are cross-examined by the combination of ultrafast electron diffraction (UED) and transient reflectivity techniques. The out-of-plane motions directly probed by reflection UED suggest a limited anisotropy in the atomic motions of monolayer MoS2, which is distinct from that of related materials such as graphene and WSe2. Besides thermal diffusion, the MoS2-sapphire interface exhibits structural dynamics trailing those of the overlaying MoS2 and are in stark contrast with the sapphire bulk, which is consistent with the limited thermal boundary conductance. These structural dynamics provide justification for the determination of carriers being trapped by defects in ∼600 fs and releasing energy within a few picoseconds. The rich findings attest to the strength of combining techniques with real-time optical and direct structure probes for a detailed understanding of dynamical processes in functional materials.
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Affiliation(s)
- Xing He
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
| | - Mazhar Chebl
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
| | - Ding-Shyue Yang
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
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8
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Berghäuser G, Bernal-Villamil I, Schmidt R, Schneider R, Niehues I, Erhart P, Michaelis de Vasconcellos S, Bratschitsch R, Knorr A, Malic E. Inverted valley polarization in optically excited transition metal dichalcogenides. Nat Commun 2018; 9:971. [PMID: 29511185 PMCID: PMC5840402 DOI: 10.1038/s41467-018-03354-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 02/07/2018] [Indexed: 11/16/2022] Open
Abstract
Large spin-orbit coupling in combination with circular dichroism allows access to spin-polarized and valley-polarized states in a controlled way in transition metal dichalcogenides. The promising application in spin-valleytronics devices requires a thorough understanding of intervalley coupling mechanisms, which determine the lifetime of spin and valley polarizations. Here we present a joint theory-experiment study shedding light on the Dexter-like intervalley coupling. We reveal that this mechanism couples A and B excitonic states in different valleys, giving rise to an efficient intervalley transfer of coherent exciton populations. We demonstrate that the valley polarization vanishes and is even inverted for A excitons, when the B exciton is resonantly excited and vice versa. Our theoretical findings are supported by energy-resolved and valley-resolved pump-probe experiments and also provide an explanation for the recently measured up-conversion in photoluminescence. The gained insights might help to develop strategies to overcome the intrinsic limit for spin and valley polarizations.
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Affiliation(s)
- Gunnar Berghäuser
- Department of Physics, Chalmers University of Technology, Gothenburg, 41296, Sweden.
| | - Ivan Bernal-Villamil
- Department of Physics, Chalmers University of Technology, Gothenburg, 41296, Sweden
| | - Robert Schmidt
- Institute of Physics and Center for Nanotechnology, University of Münster, Münster, 48149, Germany
| | - Robert Schneider
- Institute of Physics and Center for Nanotechnology, University of Münster, Münster, 48149, Germany
| | - Iris Niehues
- Institute of Physics and Center for Nanotechnology, University of Münster, Münster, 48149, Germany
| | - Paul Erhart
- Department of Physics, Chalmers University of Technology, Gothenburg, 41296, Sweden
| | | | - Rudolf Bratschitsch
- Institute of Physics and Center for Nanotechnology, University of Münster, Münster, 48149, Germany
| | - Andreas Knorr
- Institut für Theoretische Physik, Technische Universität Berlin, Berlin, 10623, Germany
| | - Ermin Malic
- Department of Physics, Chalmers University of Technology, Gothenburg, 41296, Sweden
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9
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Ye J, Yan T, Niu B, Li Y, Zhang X. Nonlinear dynamics of trions under strong optical excitation in monolayer MoSe 2. Sci Rep 2018; 8:2389. [PMID: 29403005 PMCID: PMC5799207 DOI: 10.1038/s41598-018-20810-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 01/24/2018] [Indexed: 11/09/2022] Open
Abstract
By employing ultrafast transient reflection measurements based on two-color pump-probe spectroscopy, the population and valley polarization dynamics of trions in monolayer MoSe2 were investigated at relatively high excitation densities under near-resonant excitation. Both the nonlinear dynamic photobleaching of the trion resonance and the redshift of the exciton resonance were found to be responsible for the excitation-energy- and density-dependent transient reflection change as a result of many-body interactions. Furthermore, from the polarization-resolved measurements, it was revealed that the initial fast population and polarization decay process upon strong photoexcitation observed for trions was determined by trion formation, transient phase-space filling and the short valley lifetime of excitons. The results provide a basic understanding of the nonlinear dynamics of population and valley depolarization of trions, as well as exciton-trion correlation in atomically thin MoSe2 and other transition metal dichalcogenide materials.
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Affiliation(s)
- Jialiang Ye
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
| | - Tengfei Yan
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
| | - Binghui Niu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
| | - Ying Li
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
| | - Xinhui Zhang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049, P. R. China.
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10
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Xu X, Shi Y, Liu X, Sun M. Femtosecond dynamics of monolayer MoS2-Ag nanoparticles hybrid probed at 532 nm. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2017.12.047] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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11
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Feierabend M, Malic E, Knorr A, Berghäuser G. Optical fingerprint of non-covalently functionalized transition metal dichalcogenides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:384003. [PMID: 28691918 DOI: 10.1088/1361-648x/aa7eb3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Atomically thin transition metal dichalcogenides (TMDs) hold promising potential for applications in optoelectronics. Due to their direct band gap and the extraordinarily strong Coulomb interaction, TMDs exhibit efficient light-matter coupling and tightly bound excitons. Moreover, large spin orbit coupling in combination with circular dichroism allows for spin and valley selective optical excitation. As atomically thin materials, they are very sensitive to changes in the surrounding environment. This motivates a functionalization approach, where external molecules are adsorbed to the materials surface to tailor its optical properties. Here, we apply the density matrix theory to investigate the potential of non-covalently functionalized monolayer TMDs. Considering exemplary molecules with a strong dipole moment, we predict spectral redshifts and the appearance of an additional side peak in the absorption spectrum of functionalized TMDs. We show that the molecular characteristics, e.g. coverage, orientation and dipole moment, crucially influence the optical properties of TMDs, leaving a unique optical fingerprint in the absorption spectrum. Furthermore, we find that the molecular dipole moments open a channel for coherent intervalley coupling between the high-symmetry K and [Formula: see text] points which may create new possibilities for spin-valleytronics application.
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Affiliation(s)
- Maja Feierabend
- Chalmers University of Technology, Department of Physics, SE-412 96 Gothenburg, Sweden
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12
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Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy. Sci Rep 2017; 7:40492. [PMID: 28074933 PMCID: PMC5225453 DOI: 10.1038/srep40492] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 12/06/2016] [Indexed: 12/13/2022] Open
Abstract
In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200–5000 cm−1 region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm−1 especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.
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13
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Wei K, Liu Y, Yang H, Cheng X, Jiang T. Large range modification of exciton species in monolayer WS 2. APPLIED OPTICS 2016; 55:6251-6255. [PMID: 27534466 DOI: 10.1364/ao.55.006251] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Unconventional emissions from excitons and trions in monolayer WS2 are studied by photoexcitation. When excited by a 532 nm laser beam, the carrier species in the monolayer WS2 are affected by the excess electrons escaping from photoionization of donor impurity, the concentration of which varies with different locations of the sample. Simply by increasing the excitation power at room temperature, the excess electrons and, thus, the intensity ratio of excited trions and excitons can be continuously tuned over a large range from 0.1 to 7.7. Furthermore, this intensity ratio can also be manipulated by varying temperature. However, in this way, the resonance energy of the excitons and trions shows redshifts with increasing temperature due to electron-phonon coupling. The binding energy of the trion is determined to be ∼26 meV and independent of temperature, indicating strong Coulomb interaction of carriers in such 2D materials.
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14
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Schmidt R, Berghäuser G, Schneider R, Selig M, Tonndorf P, Malić E, Knorr A, Michaelis de Vasconcellos S, Bratschitsch R. Ultrafast Coulomb-Induced Intervalley Coupling in Atomically Thin WS2. NANO LETTERS 2016; 16:2945-2950. [PMID: 27086935 DOI: 10.1021/acs.nanolett.5b04733] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Monolayers of semiconducting transition metal dichalcogenides hold the promise for a new paradigm in electronics by exploiting the valley degree of freedom in addition to charge and spin. For MoS2, WS2, and WSe2, valley polarization can be conveniently initialized and read out by circularly polarized light. However, the underlying microscopic processes governing valley polarization in these atomically thin equivalents of graphene are still not fully understood. Here, we present a joint experiment-theory study on the ultrafast time-resolved intervalley dynamics in monolayer WS2. Based on a microscopic theory, we reveal the many-particle mechanisms behind the observed spectral features. We show that Coulomb-induced intervalley coupling explains the immediate and prominent pump-probe signal in the unpumped valley and the seemingly low valley polarization degrees typically observed in pump-probe measurements compared to photoluminescence studies. The gained insights are also applicable to other light-emitting monolayer transition metal dichalcogenides, such as MoS2 and WSe2, where the Coulomb-induced intervalley coupling also determines the initial carrier dynamics.
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Affiliation(s)
- Robert Schmidt
- Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany
| | - Gunnar Berghäuser
- Department for Applied Physics, Chalmers University of Technology , SE-41296, Gothenburg, Sweden
| | - Robert Schneider
- Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany
| | - Malte Selig
- Department for Theoretical Physics, Technical University Berlin , 10623 Berlin, Germany
| | - Philipp Tonndorf
- Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany
| | - Ermin Malić
- Department for Applied Physics, Chalmers University of Technology , SE-41296, Gothenburg, Sweden
| | - Andreas Knorr
- Department for Theoretical Physics, Technical University Berlin , 10623 Berlin, Germany
| | | | - Rudolf Bratschitsch
- Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany
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In-Situ Probing Plasmonic Energy Transfer in Cu(In, Ga)Se2 Solar Cells by Ultrabroadband Femtosecond Pump-Probe Spectroscopy. Sci Rep 2015; 5:18354. [PMID: 26679958 PMCID: PMC4683378 DOI: 10.1038/srep18354] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 10/07/2015] [Indexed: 12/25/2022] Open
Abstract
In this work, we demonstrated a viable experimental scheme for in-situ probing the effects of Au nanoparticles (NPs) incorporation on plasmonic energy transfer in Cu(In, Ga)Se2 (CIGS) solar cells by elaborately analyzing the lifetimes and zero moment for hot carrier relaxation with ultrabroadband femtosecond pump-probe spectroscopy. The signals of enhanced photobleach (PB) and waned photoinduced absorption (PIA) attributable to surface plasmon resonance (SPR) of Au NPs were in-situ probed in transient differential absorption spectra. The results suggested that substantial carriers can be excited from ground state to lower excitation energy levels, which can reach thermalization much faster with the existence of SPR. Thus, direct electron transfer (DET) could be implemented to enhance the photocurrent of CIGS solar cells. Furthermore, based on the extracted hot carrier lifetimes, it was confirmed that the improved electrical transport might have been resulted primarily from the reduction in the surface recombination of photoinduced carriers through enhanced local electromagnetic field (LEMF). Finally, theoretical calculation for resonant energy transfer (RET)-induced enhancement in the probability of exciting electron-hole pairs was conducted and the results agreed well with the enhanced PB peak of transient differential absorption in plasmonic CIGS film. These results indicate that plasmonic energy transfer is a viable approach to boost high-efficiency CIGS solar cells.
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