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Wang A, Jiang X, Zheng Q, Petek H, Zhao J. Ultrafast many-body bright-dark exciton transition in anatase TiO 2. Proc Natl Acad Sci U S A 2023; 120:e2307671120. [PMID: 37956295 PMCID: PMC10666115 DOI: 10.1073/pnas.2307671120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Accepted: 09/29/2023] [Indexed: 11/15/2023] Open
Abstract
The momentum-forbidden dark excitons can have a pivotal role in quantum information processing, Bose-Einstein condensation, and light-energy harvesting. Anatase TiO2 with an indirect band gap is a prototypical platform to study bright to momentum-forbidden dark exciton transition. Here, we examine, by GW plus the real-time Bethe-Salpeter equation combined with the nonadiabatic molecular dynamics (GW + rtBSE-NAMD), the many-body transition that occurs within 100 fs from the optically excited bright to the strongly bound momentum-forbidden dark excitons in anatase TiO2. Comparing with the single-particle picture in which the exciton transition is considered to occur through electron-phonon scattering, within the GW + rtBSE-NAMD framework, the many-body electron-hole Coulomb interaction activates additional exciton relaxation channels to notably accelerate the exciton transition in competition with other radiative and nonradiative processes. The existence of dark excitons and ultrafast bright-dark exciton transitions sheds insights into applications of anatase TiO2 in optoelectronic devices and light-energy harvesting as well as the formation process of dark excitons in semiconductors.
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Affiliation(s)
- Aolei Wang
- Department of Physics, University of Science and Technology of China, Hefei230026, China
| | - Xiang Jiang
- International Center for Quantum Design of Functional Materials/Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei230026, China
| | - Qijing Zheng
- Department of Physics, University of Science and Technology of China, Hefei230026, China
| | - Hrvoje Petek
- Department of Physics and Astronomy and the IQ Initiative, University of Pittsburgh, Pittsburgh, PA15260
| | - Jin Zhao
- Department of Physics, University of Science and Technology of China, Hefei230026, China
- International Center for Quantum Design of Functional Materials/Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei230026, China
- Department of Physics and Astronomy and the IQ Initiative, University of Pittsburgh, Pittsburgh, PA15260
- Hefei National Laboratory, University of Science and Technology of China, Hefei230088, China
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2
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Saleem Y, Sadecka K, Korkusinski M, Miravet D, Dusko A, Hawrylak P. Theory of Excitons in Gated Bilayer Graphene Quantum Dots. NANO LETTERS 2023; 23:2998-3004. [PMID: 36962005 DOI: 10.1021/acs.nanolett.3c00406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
We present a theory of excitons in gated bilayer graphene (BLG) quantum dots (QDs). Electrical gating of BLG opens an energy gap, turning this material into an electrically tunable semiconductor. Unlike in laterally gated semiconductor QDs, where electrons are attracted and holes repelled, we show here that lateral structuring of metallic gates results in a gated lateral QD confining both electrons and holes. Using an accurate atomistic approach and exact diagonalization tools, we describe strongly interacting electrons and holes forming an electrically tunable exciton. We find these excitons to be different from those found in semiconductor QDs and nanocrystals, with exciton energy tunable by voltage from the terahertz to far infrared (FIR) range. The conservation of spin, valley, and orbital angular momentum results in an exciton fine structure with a band of dark low-energy states, making this system a promising candidate for storage, detection and emission of photons in the terahertz range.
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Affiliation(s)
- Yasser Saleem
- Department of Physics, University of Ottawa, Ottawa K1N6N5, Canada
| | - Katarzyna Sadecka
- Department of Physics, University of Ottawa, Ottawa K1N6N5, Canada
- Institute of Theoretical Physics, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
| | - Marek Korkusinski
- Department of Physics, University of Ottawa, Ottawa K1N6N5, Canada
- Security and Disruptive Technologies, National Research Council, Ottawa K1A0R6, Canada
| | - Daniel Miravet
- Department of Physics, University of Ottawa, Ottawa K1N6N5, Canada
| | - Amintor Dusko
- Department of Physics, University of Ottawa, Ottawa K1N6N5, Canada
| | - Pawel Hawrylak
- Department of Physics, University of Ottawa, Ottawa K1N6N5, Canada
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3
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Jiménez GC, Morinson-Negrete JD, Blanquicett FP, Ortega-López C, Espitia-Rico MJ. Effects of Mono-Vacancies and Co-Vacancies of Nitrogen and Boron on the Energetics and Electronic Properties of Heterobilayer h-BN/graphene. MATERIALS (BASEL, SWITZERLAND) 2022; 15:6369. [PMID: 36143681 PMCID: PMC9505817 DOI: 10.3390/ma15186369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Revised: 08/30/2022] [Accepted: 09/05/2022] [Indexed: 06/16/2023]
Abstract
A study is carried out which investigates the effects of the mono-vacancies of boron (VB) and nitrogen (VN) and the co-vacancies of nitrogen (N), and boron (B) on the energetics and the structural, electronic, and magnetic properties of an h-BN/graphene heterobilayer using first-principles calculations within the framework of the density functional theory (DFT). The heterobilayer is modelled using the periodic slab scheme. In the present case, a 4 × 4-(h-BN) monolayer is coupled to a 4 × 4-graphene monolayer, with a mismatch of 1.40%. In this coupling, the surface of interest is the 4 × 4-(h-BN) monolayer; the 4 × 4-graphene only represents the substrate that supports the 4 × 4-(h-BN) monolayer. From the calculations of the energy of formation of the 4 × 4-(h-BN)/4 × 4-graphene heterobilayer, with and without defects, it is established that, in both cases, the heterobilayers are energetically stable, from which it is inferred that these heterobilayers can be grown in the experiment. The formation of a mono-vacancy of boron (1 VB), a mono-vacancy of nitrogen (1 VN), and co-vacancies of boron and nitrogen (VBN) induce, on the structural level: (a) for 1 VB, a contraction n of the B-N bond lengths of ~2.46% and a slight change in the interfacial distance D (~0.096%) with respect to the heterobilayer free of defects (FD) are observed; (b) for 1 VN, a slight contraction of the B-N of bond lengths of ~0.67% and an approach between the h-BN monolayer and the graphene of ~3.83% with respect to the FD heterobilayer are observed; (c) for VBN, it can be seen that the N-N and B-B bond lengths (in the 1 VB and 1 VN regions, respectively) undergo an increase of ~2.00% and a decrease of ~3.83%, respectively. The calculations of the Löwdin charge for the FD heterobilayer and for those with defects (1 VB, 1 VN, and VBN) show that the inclusion of this type of defect induces significant changes in the Löwdin charge redistribution of the neighboring atoms of VB and VN, causing chemically active regions that could favor the interaction of the heterobilayer with external atoms and/or molecules. On the basis of an analysis of the densities of states and the band structures, it is established that the heterobilayer with 1 VB and VBN take on a half-metallic and magnetic behavior. Due to all of these properties, the FD heterobilayer and those with 1 VB, 1 VN, and VBN are candidates for possible adsorbent materials and possible materials that could be used for different spintronic applications.
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Affiliation(s)
- Gladys Casiano Jiménez
- Grupo Avanzado de Materiales y Sistemas Complejos GAMASCO, Universidad de Córdoba, Montería CP 230001, Colombia
- Doctorado en Ciencias Física, Universidad de Córdoba, Montería CP 2030001, Colombia
| | - Juan David Morinson-Negrete
- Grupo Avanzado de Materiales y Sistemas Complejos GAMASCO, Universidad de Córdoba, Montería CP 230001, Colombia
- Grupo de Investigación AMDAC, Institución Educativa José María Córdoba, Montería CP 2300001, Colombia
| | | | - César Ortega-López
- Grupo Avanzado de Materiales y Sistemas Complejos GAMASCO, Universidad de Córdoba, Montería CP 230001, Colombia
- Doctorado en Ciencias Física, Universidad de Córdoba, Montería CP 2030001, Colombia
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4
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Zhang F, Ong CS, Ruan JW, Wu M, Shi XQ, Tang ZK, Louie SG. Intervalley Excitonic Hybridization, Optical Selection Rules, and Imperfect Circular Dichroism in Monolayer h-BN. PHYSICAL REVIEW LETTERS 2022; 128:047402. [PMID: 35148132 DOI: 10.1103/physrevlett.128.047402] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 11/16/2021] [Accepted: 01/05/2022] [Indexed: 06/14/2023]
Abstract
We perform first-principles GW plus Bethe-Salpeter equation calculations to investigate the photophysics of monolayer hexagonal boron nitride (h-BN), revealing excitons with novel k-space characteristics. The excitonic states forming the first and third peaks in its absorption spectrum are s-like, but those of the second peak are notably p-like, a first finding of strong co-occurrence of bright s-like and bright p-like states in an intrinsic 2D material. Moreover, even though the k-space wave function of these excitonic states are centered at the K and K^{'} valleys as in monolayer transition metal dichalcogenides, the k-space envelope functions of the basis excitons at one valley have significant extents to the basin of the other valley. As a consequence, the optical response of monolayer h-BN exhibits a lack of circular dichroism, as well as a coupling that induces an intervalley mixing between s- and p-like states.
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Affiliation(s)
- Fang Zhang
- Institute of Applied Physics and Materials Engineering, University of Macau, Macau S.A.R. 999078, China
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Physics, Southern University of Science and Technology, ShenZhen 518000, China
| | - Chin Shen Ong
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Jia Wei Ruan
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Meng Wu
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Xing Qiang Shi
- Department of Physics, Southern University of Science and Technology, ShenZhen 518000, China
| | - Zi Kang Tang
- Institute of Applied Physics and Materials Engineering, University of Macau, Macau S.A.R. 999078, China
| | - Steven G Louie
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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5
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Xie K, Li X, Cao T. Theory and Ab Initio Calculation of Optically Excited States-Recent Advances in 2D Materials. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e1904306. [PMID: 31808581 DOI: 10.1002/adma.201904306] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 09/19/2019] [Indexed: 05/16/2023]
Abstract
Recent studies of the optical properties of 2D materials have reported unique phenomena and features that are absent in conventional bulk semiconductors. Many of these interesting properties, such as enhanced light-matter coupling, gate-tunable photoluminescence, and unusual excitonic optical selection rules arise from the nature of the two- and multi-particle excited states such as strongly bound Wannier excitons and charged excitons. The theory, modeling, and ab initio calculations of these optically excited states in 2D materials are reviewed. Several analytical and ab initio approaches are introduced. These methods are compared with each other, revealing their relative strength and limitations. Recent works that apply these methods to a variety of 2D materials and material-defect systems are then highlighted. Understanding of the optically excited states in these systems is relevant not only for fundamental scientific research of electronic excitations and correlations, but also plays an important role in the future development of quantum information science and nano-photonics.
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Affiliation(s)
- Kaichen Xie
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
| | - Xiaosong Li
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
- Department of Chemistry, University of Washington, Seattle, WA, 98195, USA
| | - Ting Cao
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
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6
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Perfetto E, Stefanucci G. Floquet Topological Phase of Nondriven p-Wave Nonequilibrium Excitonic Insulators. PHYSICAL REVIEW LETTERS 2020; 125:106401. [PMID: 32955296 DOI: 10.1103/physrevlett.125.106401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 08/14/2020] [Indexed: 06/11/2023]
Abstract
The nontrivial topology of p-wave superfluids makes these systems attractive candidates in information technology. In this work we report on the topological state of a p-wave nonequilibrium excitonic insulator (NEQ-EI) and show how to steer a nontopological band insulator with bright p excitons toward this state by a suitable laser pulse, thus achieving a dynamical topological phase transition. The underlying mechanism behind the transition is the broken gauge-symmetry of the NEQ-EI which causes self-sustained persistent oscillations of the excitonic condensate and hence a Floquet topological state for high enough exciton densities. We show the formation of Floquet Majorana modes at the boundaries of the open system and discuss unique topological spectral signatures for time-resolved ARPES experiments. We emphasize that the topological properties of a p-wave NEQ-EI arise exclusively from the electron-hole Coulomb interaction as the system is not driven by external fields.
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Affiliation(s)
- E Perfetto
- Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
- INFN, Sezione di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
| | - G Stefanucci
- Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
- INFN, Sezione di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
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7
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Guo H, Zhang R, Li H, Wang X, Lu H, Qian K, Li G, Huang L, Lin X, Zhang YY, Ding H, Du S, Pantelides ST, Gao HJ. Sizable Band Gap in Epitaxial Bilayer Graphene Induced by Silicene Intercalation. NANO LETTERS 2020; 20:2674-2680. [PMID: 32125162 DOI: 10.1021/acs.nanolett.0c00306] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Opening a band gap in bilayer graphene (BLG) is of significance for potential applications in graphene-based electronic and photonic devices. Here, we report the generation of a sizable band gap in BLG by intercalating silicene between BLG and Ru substrate. We first grow high-quality Bernal-stacked BLG on Ru(0001) and then intercalate silicene to the interface between the BLG and Ru, which is confirmed by low-energy electron diffraction and scanning tunneling microscopy. Raman spectroscopy shows that the G and 2D peaks of the intercalated BLG are restored to the freestanding-BLG features. Angle-resolved photoelectron spectroscopy measurements show that a band gap of about 0.2 eV opens in the BLG. Density functional theory calculations indicate that the large-gap opening results from a cooperative contribution of the doping and rippling/strain in the BLG. This work provides insightful understanding on the mechanism of band gap opening in BLG and enhances the potential of graphene-based device development.
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Affiliation(s)
- Hui Guo
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Ruizi Zhang
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Hang Li
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Xueyan Wang
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Hongliang Lu
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Kai Qian
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Geng Li
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Li Huang
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Xiao Lin
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Yu-Yang Zhang
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, P.R. China
| | - Hong Ding
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, P.R. China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, P.R. China
| | - Shixuan Du
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, P.R. China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, P.R. China
| | - Sokrates T Pantelides
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
- Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Hong-Jun Gao
- Institute of Physics and University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, P.R. China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, P.R. China
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8
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Cao T, Wu M, Louie SG. Unifying Optical Selection Rules for Excitons in Two Dimensions: Band Topology and Winding Numbers. PHYSICAL REVIEW LETTERS 2018; 120:087402. [PMID: 29543006 DOI: 10.1103/physrevlett.120.087402] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 10/03/2017] [Indexed: 05/20/2023]
Abstract
We show that band topology can dramatically change the photophysics of two-dimensional semiconductors. For systems in which states near the band extrema are of multicomponent character, the spinors describing these components (pseudospins) can pick up nonzero winding numbers around the extremal k point. In these systems, we find that the strength and required light polarization of an excitonic optical transition are dictated by the optical matrix element winding number, a unique and heretofore unrecognized topological characteristic. We illustrate these findings in three gapped graphene systems-monolayer graphene with inequivalent sublattices and biased bi- and trilayer graphene, where the pseudospin textures manifest into nontrivial optical matrix element winding numbers associated with different valley and photon circular polarization. This winding-number physics leads to novel exciton series and optical selection rules, with each valley hosting multiple bright excitons coupled to light of different circular polarization. This valley-exciton selective circular dichroism can be unambiguously detected using optical spectroscopy.
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Affiliation(s)
- Ting Cao
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Meng Wu
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Steven G Louie
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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9
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Ju L, Wang L, Cao T, Taniguchi T, Watanabe K, Louie SG, Rana F, Park J, Hone J, Wang F, McEuen PL. Tunable excitons in bilayer graphene. Science 2017; 358:907-910. [DOI: 10.1126/science.aam9175] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Accepted: 10/05/2017] [Indexed: 11/02/2022]
Abstract
Excitons, the bound states of an electron and a hole in a solid material, play a key role in the optical properties of insulators and semiconductors. Here, we report the observation of excitons in bilayer graphene (BLG) using photocurrent spectroscopy of high-quality BLG encapsulated in hexagonal boron nitride. We observed two prominent excitonic resonances with narrow line widths that are tunable from the mid-infrared to the terahertz range. These excitons obey optical selection rules distinct from those in conventional semiconductors and feature an electron pseudospin winding number of 2. An external magnetic field induces a large splitting of the valley excitons, corresponding to a g-factor of about 20. These findings open up opportunities to explore exciton physics with pseudospin texture in electrically tunable graphene systems.
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Affiliation(s)
- Long Ju
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA
| | - Lei Wang
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA
| | - Ting Cao
- Department of Physics, University of California, Berkeley, CA 94720, 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
| | - Steven G. Louie
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Farhan Rana
- School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Jiwoong Park
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA
| | - Feng Wang
- Department of Physics, University of California, Berkeley, CA 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Kavli Energy NanoSciences Institute at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Paul L. McEuen
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA
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10
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Brinkley MK, Abergel DSL, Clader BD. Two-photon absorption in gapped bilayer graphene with a tunable chemical potential. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:365001. [PMID: 27392275 DOI: 10.1088/0953-8984/28/36/365001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Despite the now vast body of two-dimensional materials under study, bilayer graphene remains unique in two ways: it hosts a simultaneously tunable band gap and electron density; and stems from simple fabrication methods. These two advantages underscore why bilayer graphene is critical as a material for optoelectronic applications. In the work that follows, we calculate the one- and two-photon absorption coefficients for degenerate interband absorption in a graphene bilayer hosting an asymmetry gap and adjustable chemical potential-all at finite temperature. Our analysis is comprehensive, characterizing one- and two-photon absorptive behavior over wide ranges of photon energy, gap, chemical potential, and thermal broadening. The two-photon absorption coefficient for bilayer graphene displays a rich structure as a function of photon energy and band gap due to the existence of multiple absorption pathways and the nontrivial dispersion of the low energy bands. This systematic work will prove integral to the design of bilayer-graphene-based nonlinear optical devices.
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Affiliation(s)
- M K Brinkley
- Research and Exploratory Development Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20973, USA
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11
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Rösner M, Steinke C, Lorke M, Gies C, Jahnke F, Wehling TO. Two-Dimensional Heterojunctions from Nonlocal Manipulations of the Interactions. NANO LETTERS 2016; 16:2322-2327. [PMID: 26918626 DOI: 10.1021/acs.nanolett.5b05009] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We propose to create lateral heterojunctions in two-dimensional materials based on nonlocal manipulations of the Coulomb interaction using structured dielectric environments. By means of ab initio calculations for MoS2 as well as generic semiconductor models, we show that the Coulomb interaction-induced self-energy corrections in real space are sufficiently nonlocal to be manipulated externally, but still local enough to induce spatially sharp interfaces within a single homogeneous monolayer to form heterojunctions. We find a type-II heterojunction band scheme promoted by a laterally structured dielectric environment, which exhibits a sharp band gap crossover within less than 5 unit cells.
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Affiliation(s)
- M Rösner
- Institut für Theoretische Physik, Universität Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
- Bremen Center for Computational Materials Science, Universität Bremen , Am Fallturm 1a, 28359 Bremen, Germany
| | - C Steinke
- Institut für Theoretische Physik, Universität Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
- Bremen Center for Computational Materials Science, Universität Bremen , Am Fallturm 1a, 28359 Bremen, Germany
| | - M Lorke
- Institut für Theoretische Physik, Universität Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
| | - C Gies
- Institut für Theoretische Physik, Universität Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
| | - F Jahnke
- Institut für Theoretische Physik, Universität Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
| | - T O Wehling
- Institut für Theoretische Physik, Universität Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
- Bremen Center for Computational Materials Science, Universität Bremen , Am Fallturm 1a, 28359 Bremen, Germany
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12
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First-principles study of the interaction of hydrogen molecular on Na-adsorbed graphene. APPLIED NANOSCIENCE 2014. [DOI: 10.1007/s13204-014-0329-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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13
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Sensitive and selective DNA probe based on “turn-on” photoluminescence of C-dots@RGO. Anal Bioanal Chem 2014; 406:6917-23. [DOI: 10.1007/s00216-014-7658-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Revised: 01/06/2014] [Accepted: 01/23/2014] [Indexed: 11/26/2022]
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14
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Wang XM, Mo DC, Lu SS. On the thermoelectric transport properties of graphyne by the first-principles method. J Chem Phys 2013; 138:204704. [DOI: 10.1063/1.4806069] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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15
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McCann E, Koshino M. The electronic properties of bilayer graphene. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2013; 76:056503. [PMID: 23604050 DOI: 10.1088/0034-4885/76/5/056503] [Citation(s) in RCA: 201] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
We review the electronic properties of bilayer graphene, beginning with a description of the tight-binding model of bilayer graphene and the derivation of the effective Hamiltonian describing massive chiral quasiparticles in two parabolic bands at low energies. We take into account five tight-binding parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra- and interlayer asymmetry between atomic sites which induce band gaps in the low-energy spectrum. The Hartree model of screening and band-gap opening due to interlayer asymmetry in the presence of external gates is presented. The tight-binding model is used to describe optical and transport properties including the integer quantum Hall effect, and we also discuss orbital magnetism, phonons and the influence of strain on electronic properties. We conclude with an overview of electronic interaction effects.
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Affiliation(s)
- Edward McCann
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
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16
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17
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18
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Roslyak O, Gumbs G, Mukamel S. Trapping photon-dressed Dirac electrons in a quantum dot studied by coherent two dimensional photon echo spectroscopy. J Chem Phys 2012; 136:194106. [PMID: 22612079 PMCID: PMC4108635 DOI: 10.1063/1.4707182] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Accepted: 04/11/2012] [Indexed: 11/14/2022] Open
Abstract
We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated.
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Affiliation(s)
- O Roslyak
- Department of Physics, Hunter College, City University of New York, 695 Park Avenue, New York, New York 10065, USA.
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19
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Kaloni TP, Cheng YC, Schwingenschlögl U. Electronic structure of superlattices of graphene and hexagonal boron nitride. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c1jm14895h] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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20
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Wang P, Zhai Y, Wang D, Dong S. Synthesis of reduced graphene oxide-anatase TiO2 nanocomposite and its improved photo-induced charge transfer properties. NANOSCALE 2011; 3:1640-1645. [PMID: 21286599 DOI: 10.1039/c0nr00714e] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The construction of reduced graphene oxide or graphene oxide with semiconductor has gained more and more attention due to its unexpected optoelectronic and electronic properties. The synthesis of reduced graphene oxide (RGO) or graphene oxide-semiconductor nanocomposite with well-dispersed decorated particles is still a challenge now. Herein, we demonstrate a facile method for the synthesis of graphene oxide-amorphous TiO(2) and reduced graphene oxide-anatase TiO(2) nanocomposites with well-dispersed particles. The as-synthesized samples were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy, Fourier transform infrared spectrometry, and thermogravimetric analysis. The photovoltaic properties of RGO-anatase TiO(2) were also compared with that of similar sized anatase TiO(2) by transient photovoltage technique, and it was interesting to find that the combination of reduced graphene oxide with anatase TiO(2) will significantly increase the photovoltaic response and retard the recombination of electron-hole pairs in the excited anatase TiO(2).
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Affiliation(s)
- Ping Wang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, PR China
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21
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Mak KF, Shan J, Heinz TF. Seeing many-body effects in single- and few-layer graphene: observation of two-dimensional saddle-point excitons. PHYSICAL REVIEW LETTERS 2011; 106:046401. [PMID: 21405342 DOI: 10.1103/physrevlett.106.046401] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Indexed: 05/22/2023]
Abstract
Significant excitonic effects were observed in graphene by measuring its optical conductivity in a broad spectral range including the two-dimensional π-band saddle-point singularities in the electronic structure. The strong electron-hole interactions manifest themselves in an asymmetric resonance peaked at 4.62 eV, which is redshifted by nearly 600 meV from the value predicted by ab initio GW calculations for the band-to-band transitions. The observed excitonic resonance is explained within a phenomenological model as a Fano interference of a strongly coupled excitonic state and a band continuum. Our experiment also showed a weak dependence of the excitonic resonance in few-layer graphene on layer thickness. This result reflects the effective cancellation of the increasingly screened repulsive electron-electron (e-e) and attractive electron-hole (e-h) interactions.
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Affiliation(s)
- Kin Fai Mak
- Department of Physics, Columbia University, New York, New York 10027, USA
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22
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Bao W, Zhao Z, Zhang H, Liu G, Kratz P, Jing L, Velasco J, Smirnov D, Lau CN. Magnetoconductance oscillations and evidence for fractional quantum Hall states in suspended bilayer and trilayer graphene. PHYSICAL REVIEW LETTERS 2010; 105:246601. [PMID: 21231541 DOI: 10.1103/physrevlett.105.246601] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Indexed: 05/30/2023]
Abstract
We report pronounced magnetoconductance oscillations observed on suspended bilayer and trilayer graphene devices with mobilities up to 270,000 cm²/V s. For bilayer devices, we observe conductance minima at all integer filling factors ν between 0 and -8, as well as a small plateau at ν=1/3. For trilayer devices, we observe features at ν=-1, -2, -3, and -4, and at ν∼0.5 that persist to 4.5 K at B=8 T. All of these features persist for all accessible values of Vg and B, and could suggest the onset of symmetry breaking of the first few Landau levels and fractional quantum Hall states.
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Affiliation(s)
- Wenzhong Bao
- Department of Physics, University of California, Riverside, Riverside, California 92521, USA
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23
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Lee S, Lee K, Zhong Z. Wafer scale homogeneous bilayer graphene films by chemical vapor deposition. NANO LETTERS 2010; 10:4702-7. [PMID: 20932046 DOI: 10.1021/nl1029978] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The discovery of electric field induced band gap opening in bilayer graphene opens a new door for making semiconducting graphene without aggressive size scaling or using expensive substrates. However, bilayer graphene samples have been limited to μm(2) size scale thus far, and synthesis of wafer scale bilayer graphene poses a tremendous challenge. Here we report homogeneous bilayer graphene films over at least a 2 in. × 2 in. area, synthesized by chemical vapor deposition on copper foil and subsequently transferred to arbitrary substrates. The bilayer nature of graphene film is verified by Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Importantly, spatially resolved Raman spectroscopy confirms a bilayer coverage of over 99%. The homogeneity of the film is further supported by electrical transport measurements on dual-gate bilayer graphene transistors, in which a band gap opening is observed in 98% of the devices.
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Affiliation(s)
- Seunghyun Lee
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, United States
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Jing L, Velasco J, Kratz P, Liu G, Bao W, Bockrath M, Lau CN. Quantum transport and field-induced insulating states in bilayer graphene pnp junctions. NANO LETTERS 2010; 10:4000-4004. [PMID: 20863070 DOI: 10.1021/nl101901g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We perform transport measurements in high quality bilayer graphene pnp junctions with suspended top gates. At a magnetic field B = 0, we demonstrate band gap opening by an applied perpendicular electric field with an On/Off ratio up to 20,000 at 260 mK. Within the band gap, the conductance decreases exponentially by 3 orders of magnitude with increasing electric field and can be accounted for by variable range hopping with a gate-tunable density of states, effective mass, and localization length. At large B, we observe quantum Hall conductance with fractional values, which arise from equilibration of edge states between differentially doped regions, and the presence of an insulating state at filling factor v = 0. Our work underscores the importance of bilayer graphene for both fundamental interest and technological applications.
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Affiliation(s)
- Lei Jing
- Department of Physics, University of California, Riverside, California 92521, USA
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