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Jiang Y, Chen S, Zheng W, Zheng B, Pan A. Interlayer exciton formation, relaxation, and transport in TMD van der Waals heterostructures. LIGHT, SCIENCE & APPLICATIONS 2021; 10:72. [PMID: 33811214 PMCID: PMC8018964 DOI: 10.1038/s41377-021-00500-1] [Citation(s) in RCA: 92] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 02/08/2021] [Accepted: 02/24/2021] [Indexed: 05/06/2023]
Abstract
Van der Waals (vdW) heterostructures based on transition metal dichalcogenides (TMDs) generally possess a type-II band alignment that facilitates the formation of interlayer excitons between constituent monolayers. Manipulation of the interlayer excitons in TMD vdW heterostructures holds great promise for the development of excitonic integrated circuits that serve as the counterpart of electronic integrated circuits, which allows the photons and excitons to transform into each other and thus bridges optical communication and signal processing at the integrated circuit. As a consequence, numerous studies have been carried out to obtain deep insight into the physical properties of interlayer excitons, including revealing their ultrafast formation, long population recombination lifetimes, and intriguing spin-valley dynamics. These outstanding properties ensure interlayer excitons with good transport characteristics, and may pave the way for their potential applications in efficient excitonic devices based on TMD vdW heterostructures. At present, a systematic and comprehensive overview of interlayer exciton formation, relaxation, transport, and potential applications is still lacking. In this review, we give a comprehensive description and discussion of these frontier topics for interlayer excitons in TMD vdW heterostructures to provide valuable guidance for researchers in this field.
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Affiliation(s)
- Ying Jiang
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics, and College of Materials Science and Engineering, Hunan University, Changsha, China
| | - Shula Chen
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics, and College of Materials Science and Engineering, Hunan University, Changsha, China
- Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China
| | - Weihao Zheng
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics, and College of Materials Science and Engineering, Hunan University, Changsha, China
| | - Biyuan Zheng
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics, and College of Materials Science and Engineering, Hunan University, Changsha, China
| | - Anlian Pan
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronics, and College of Materials Science and Engineering, Hunan University, Changsha, China.
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2
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Transparency of Land Administration and the Role of Blockchain Technology, a Four-Dimensional Framework Analysis from the Ghanaian Land Perspective. LAND 2020. [DOI: 10.3390/land9120491] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Existing studies on blockchain within land administration have focused mainly on replacing or complementing the technology for land registration and titling. This study explores the potential of using blockchain technology to enhance the transparency of all land administration processes using an integrative review methodology coupled with a framework analysis. This study draws on the Ghanaian land administration perspective to make this insightful. It appears possible to apply a permissionless public blockchain across all land administration processes. This integrates all departments, processes, and stakeholders of land administration to enhance openness, improve availability and accessibility to information, and foster participation for transparency simultaneously. This can change the transparency variation in land administration to be more equal and homogenous regardless of land type. This, however, depends on the standardization of processes across the divisions, as well as negotiation and consensus amongst all stakeholders, especially with chiefs. Limitations include: limited storage and scalability, as well as huge electricity consumption for operation. This study’s policy implications are a review of all paper-based land transactions, a comprehensive digitization of land administration processes, public–private partnership on blockchain-based land administration, and professionals and stakeholder education on the technology.
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Wang J, Nie P, Li X, Zuo H, Fauqué B, Zhu Z, Behnia K. Critical point for Bose-Einstein condensation of excitons in graphite. Proc Natl Acad Sci U S A 2020; 117:30215-30219. [PMID: 33199600 PMCID: PMC7720211 DOI: 10.1073/pnas.2012811117] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
An exciton is an electron-hole pair bound by attractive Coulomb interaction. Short-lived excitons have been detected by a variety of experimental probes in numerous contexts. An excitonic insulator, a collective state of such excitons, has been more elusive. Here, thanks to Nernst measurements in pulsed magnetic fields, we show that in graphite there is a critical temperature (T = 9.2 K) and a critical magnetic field (B = 47 T) for Bose-Einstein condensation of excitons. At this critical field, hole and electron Landau subbands simultaneously cross the Fermi level and allow exciton formation. By quantifying the effective mass and the spatial separation of the excitons in the basal plane, we show that the degeneracy temperature of the excitonic fluid corresponds to this critical temperature. This identification would explain why the field-induced transition observed in graphite is not a universal feature of three-dimensional electron systems pushed beyond the quantum limit.
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Affiliation(s)
- Jinhua Wang
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
- School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Pan Nie
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
- School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Xiaokang Li
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
- School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Huakun Zuo
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
- School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Benoît Fauqué
- Jeunes Équipes de l'Institut de Physique, Unité Mixte de Service et de Recherche 3573, CNRS, Collège de France, Paris Sciences et Lettres Research University, 75231 Paris Cedex 05, France
| | - Zengwei Zhu
- Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China;
- School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Kamran Behnia
- Laboratoire de Physique et d'Étude des Matériaux, CNRS, École Supérieure de Physique et de Chimie Industrielles Paris, Paris Sciences et Lettres Research University, 75005 Paris, France
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Gupta S, Kutana A, Yakobson BI. Heterobilayers of 2D materials as a platform for excitonic superfluidity. Nat Commun 2020; 11:2989. [PMID: 32533022 PMCID: PMC7293212 DOI: 10.1038/s41467-020-16737-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 05/13/2020] [Indexed: 11/12/2022] Open
Abstract
Excitonic condensate has been long-sought within bulk indirect-gap semiconductors, quantum wells, and 2D material layers, all tried as carrying media. Here, we propose intrinsically stable 2D semiconductor heterostructures with doubly-indirect overlapping bands as optimal platforms for excitonic condensation. After screening hundreds of 2D materials, we identify candidates where spontaneous excitonic condensation mediated by purely electronic interaction should occur, and hetero-pairs Sb2Te2Se/BiTeCl, Hf2N2I2/Zr2N2Cl2, and LiAlTe2/BiTeI emerge promising. Unlike monolayers, where excitonic condensation is hampered by Peierls instability, or other bilayers, where doping by applied voltage is required, rendering them essentially non-equilibrium systems, the chemically-specific heterostructures predicted here are lattice-matched, show no detrimental electronic instability, and display broken type-III gap, thus offering optimal carrier density without any gate voltages, in true-equilibrium. Predicted materials can be used to access different parts of electron-hole phase diagram, including BEC-BCS crossover, enabling tantalizing applications in superfluid transport, Josephson-like tunneling, and dissipationless charge counterflow.
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Affiliation(s)
- Sunny Gupta
- Materials Science and NanoEngineering, Rice University, Houston, TX, 77005, USA
| | - Alex Kutana
- Materials Science and NanoEngineering, Rice University, Houston, TX, 77005, USA
| | - Boris I Yakobson
- Materials Science and NanoEngineering, Rice University, Houston, TX, 77005, USA.
- Department of Chemistry, Rice University, Houston, TX, 77005, USA.
- Smalley-Curl Institute for Nanoscale Science and Technology, Rice University, Houston, TX, 77005, USA.
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Wang Z, Rhodes DA, Watanabe K, Taniguchi T, Hone JC, Shan J, Mak KF. Evidence of high-temperature exciton condensation in two-dimensional atomic double layers. Nature 2019; 574:76-80. [PMID: 31578483 DOI: 10.1038/s41586-019-1591-7] [Citation(s) in RCA: 139] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2019] [Accepted: 08/16/2019] [Indexed: 11/09/2022]
Abstract
A Bose-Einstein condensate is the ground state of a dilute gas of bosons, such as atoms cooled to temperatures close to absolute zero1. With much smaller mass, excitons (bound electron-hole pairs) are expected to condense at considerably higher temperatures2-7. Two-dimensional van der Waals semiconductors with very strong exciton binding are ideal systems for the study of high-temperature exciton condensation. Here we study electrically generated interlayer excitons in MoSe2-WSe2 atomic double layers with a density of up to 1012 excitons per square centimetre. The interlayer tunnelling current depends only on the exciton density, which is indicative of correlated electron-hole pair tunnelling8. Strong electroluminescence arises when a hole tunnels from WSe2 to recombine with an electron in MoSe2. We observe a critical threshold dependence of the electroluminescence intensity on exciton density, accompanied by super-Poissonian photon statistics near the threshold, and a large electroluminescence enhancement with a narrow peak at equal electron and hole densities. The phenomenon persists above 100 kelvin, which is consistent with the predicted critical condensation temperature9-12. Our study provides evidence for interlayer exciton condensation in two-dimensional atomic double layers and opens up opportunities for exploring condensate-based optoelectronics and exciton-mediated high-temperature superconductivity13.
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Affiliation(s)
- Zefang Wang
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Daniel A Rhodes
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - James C Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Jie Shan
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA. .,Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA. .,Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
| | - Kin Fai Mak
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA. .,Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA. .,Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
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6
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Rivera P, Yu H, Seyler KL, Wilson NP, Yao W, Xu X. Interlayer valley excitons in heterobilayers of transition metal dichalcogenides. NATURE NANOTECHNOLOGY 2018; 13:1004-1015. [PMID: 30104622 DOI: 10.1038/s41565-018-0193-0] [Citation(s) in RCA: 172] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Accepted: 06/11/2018] [Indexed: 05/12/2023]
Abstract
Stacking different two-dimensional crystals into van der Waals heterostructures provides an exciting approach to designing quantum materials that can harness and extend the already fascinating properties of the constituents. Heterobilayers of transition metal dichalcogenides are particularly attractive for low-dimensional semiconductor optics because they host interlayer excitons-with electrons and holes localized in different layers-which inherit valley-contrasting physics from the monolayers and thereby possess various novel and appealing properties compared to other solid-state nanostructures. This Review presents the contemporary experimental and theoretical understanding of these interlayer excitons. We discuss their unique optical properties arising from the underlying valley physics, the strong many-body interactions and electrical control resulting from the electric dipole moment, and the unique effects of a moiré superlattice on the interlayer exciton potential landscape and optical properties.
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Affiliation(s)
- Pasqual Rivera
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Hongyi Yu
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - Kyle L Seyler
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Nathan P Wilson
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China.
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
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Kovalev VM, Tse WK. Relaxation dynamics of a driven two-level system coupled to a Bose-Einstein condensate: application to quantum dot-dipolar exciton gas hybrid systems. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:465301. [PMID: 28862151 DOI: 10.1088/1361-648x/aa89c2] [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
We develop a microscopic theory for the relaxation dynamics of an optically pumped two-level system (TLS) coupled to a bath of weakly interacting Bose gas. Using Keldysh formalism and diagrammatic perturbation theory, expressions for the relaxation times of the TLS Rabi oscillations are derived when the boson bath is in the normal state and the Bose-Einstein condensate (BEC) state. We apply our general theory to consider an irradiated quantum dot coupled with a boson bath consisting of a two-dimensional dipolar exciton gas. When the bath is in the BEC regime, relaxation of the Rabi oscillations is due to both condensate and non-condensate fractions of the bath bosons for weak TLS-light coupling and pre dominantly due to the non-condensate fraction for strong TLS-light coupling. Our theory also shows that a phase transition of the bath from the normal to the BEC state strongly influences the relaxation rate of the TLS Rabi oscillations. The TLS relaxation rate is approximately independent of the pump field frequency and monotonically dependent on the field strength when the bath is in the low-temperature regime of the normal phase. Phase transition of the dipolar exciton gas leads to a non-monotonic dependence of the TLS relaxation rate on both the pump field frequency and field strength, providing a characteristic signature for the detection of BEC phase transition of the coupled dipolar exciton gas.
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Affiliation(s)
- Vadim M Kovalev
- Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Sciences, Novosibirsk 630090, Russia. Department of Applied and Theoretical Physics, Novosibirsk State Technical University, Novosibirsk 630073, Russia
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8
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Kyriienko O, Kibis OV, Shelykh IA. Floquet control of dipolaritons in quantum wells. OPTICS LETTERS 2017; 42:2398-2401. [PMID: 28614320 DOI: 10.1364/ol.42.002398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 05/27/2017] [Indexed: 06/07/2023]
Abstract
We developed the theory of dipolaritons in semiconductor quantum wells irradiated by an off-resonant electromagnetic wave (dressing field). Solving the Floquet problem for the dressed dipolaritons, we demonstrated that the field drastically modifies all dipolaritonic properties. In particular, the dressing field strongly affects the terahertz emission from the considered system. The described effect paves the way for optical control of prospective dipolariton-based terahertz devices.
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9
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Combescot M, Combescot R, Dubin F. Bose-Einstein condensation and indirect excitons: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:066501. [PMID: 28355164 DOI: 10.1088/1361-6633/aa50e3] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We review recent progress on Bose-Einstein condensation (BEC) of semiconductor excitons. The first part deals with theory, the second part with experiments. This Review is written at a time where the problem of exciton Bose-Einstein condensation has just been revived by the understanding that the exciton condensate must be dark because the exciton ground state is not coupled to light. Here, we theoretically discuss this missed understanding before providing its experimental support through experiments that scrutinize indirect excitons made of spatially separated electrons and holes. The theoretical part first discusses condensation of elementary bosons. In particular, the necessary inhibition of condensate fragmentation by exchange interaction is stressed, before extending the discussion to interacting bosons with spin degrees of freedom. The theoretical part then considers composite bosons made of two fermions like semiconductor excitons. The spin structure of the excitons is detailed, with emphasis on the crucial fact that ground-state excitons are dark: indeed, this imposes the exciton Bose-Einstein condensate to be not coupled to light in the dilute regime. Condensate fragmentations are then reconsidered. In particular, it is shown that while at low density, the exciton condensate is fully dark, it acquires a bright component, coherent with the dark one, beyond a density threshold: in this regime, the exciton condensate is 'gray'. The experimental part first discusses optical creation of indirect excitons in quantum wells, and the detection of their photoluminescence. Exciton thermalisation is also addressed, as well as available approaches to estimate the exciton density. We then switch to specific experiments where indirect excitons form a macroscopic fragmented ring. We show that such ring provides efficient electrostatic trapping in the region of the fragments where an essentially-dark exciton Bose-Einstein condensate is formed at sub-Kelvin bath temperatures. The macroscopic spatial coherence of the photoluminescence observed in this essentially dark region confirms this conclusion.
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Affiliation(s)
- Monique Combescot
- Institut des NanoSciences de Paris, Université Pierre et Marie Curie, CNRS, Tour 22, 4 place Jussieu, 75005 Paris, France
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10
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Berman OL, Kezerashvili RY, Kolmakov GV, Pomirchi LM. Spontaneous formation and nonequilibrium dynamics of a soliton-shaped Bose-Einstein condensate in a trap. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:062901. [PMID: 26172766 DOI: 10.1103/physreve.91.062901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Indexed: 06/04/2023]
Abstract
The Bose-stimulated self-organization of a quasi-two-dimensional nonequilibrium Bose-Einstein condensate in an in-plane potential is proposed. We obtained the solution of the nonlinear, driven-dissipative Gross-Pitaevskii equation for a Bose-Einstein condensate trapped in an external asymmetric parabolic potential within the method of the spectral expansion. We found that, in sharp contrast to previous observations, the condensate can spontaneously acquire a solitonlike shape for spatially homogeneous pumping. This condensate soliton performs oscillatory motion in a parabolic trap and, also, can spontaneously rotate. Stability of the condensate soliton in the spatially asymmetric trap is analyzed. In addition to the nonlinear dynamics of nonequilibrium Bose-Einstein condensates of ultracold atoms, our findings can be applied to the condensates of quantum well excitons and cavity polaritons in semiconductor heterostructure, and to the condensates of photons.
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Affiliation(s)
- Oleg L Berman
- Physics Department, New York City College of Technology, The City University of New York, Brooklyn, New York 11201, USA
| | - Roman Ya Kezerashvili
- Physics Department, New York City College of Technology, The City University of New York, Brooklyn, New York 11201, USA
| | - German V Kolmakov
- Physics Department, New York City College of Technology, The City University of New York, Brooklyn, New York 11201, USA
| | - Leonid M Pomirchi
- Physics Department, New York City College of Technology, The City University of New York, Brooklyn, New York 11201, USA
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11
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Pinsker F, Flayac H. On-demand dark soliton train manipulation in a spinor polariton condensate. PHYSICAL REVIEW LETTERS 2014; 112:140405. [PMID: 24765927 DOI: 10.1103/physrevlett.112.140405] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Indexed: 06/03/2023]
Abstract
We theoretically demonstrate the generation of dark soliton trains in a one-dimensional exciton-polariton condensate within experimentally accessible schemes. In particular, we show that the frequency of the train can be finely tuned fully optically or electrically to provide a stable and efficient output signal modulation. Taking the polarization of the condensate into account, we elucidate the possibility of forming on-demand half-soliton trains.
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Affiliation(s)
- F Pinsker
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom
| | - H Flayac
- Institute of Theoretical Physics, École Polytechnique Fédérale de Lausanne EPFL, CH-1015 Lausanne, Switzerland
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12
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Su JJ, Kim NY, Yamamoto Y, Macdonald AH. Ferminoic physics in dipolariton condensates. PHYSICAL REVIEW LETTERS 2014; 112:116401. [PMID: 24702391 DOI: 10.1103/physrevlett.112.116401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Indexed: 06/03/2023]
Abstract
An exciton polariton is an extremely light bosonic quasiparticle that is composed of an exciton and a photon. We report on a theoretical study of exciton-polariton condensation in a system with tunnel-coupled quantum wells. Because their excitons can carry an electric dipole moment, these systems have been referred to as dipolariton condensates. We use a fermionic mean-field theory that can address quantum well and other internal exciton degrees of freedom to describe the new physics present in dipolariton condensates. We find that the role of underlying fermonic degrees of freedom is enhanced and predict that metallic condensates can occur at high carrier densities.
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Affiliation(s)
- Jung-Jung Su
- National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan and Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305-4085, USA and Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan
| | - Na Young Kim
- Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305-4085, USA
| | - Yoshihisa Yamamoto
- National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan and Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305-4085, USA
| | - Allan H Macdonald
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
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13
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Andreev SV, Varlamov AA, Kavokin AV. Scale invariance and universality in a cold gas of indirect excitons. PHYSICAL REVIEW LETTERS 2014; 112:036401. [PMID: 24484149 DOI: 10.1103/physrevlett.112.036401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2013] [Indexed: 06/03/2023]
Abstract
We address, theoretically, the puzzling similarity observed in the thermodynamic behavior of independent clouds of cold dipolar excitons in coupled semiconductor quantum wells. We argue that the condensation of self-trapped exciton gas starts at the same critical temperature in all traps due to the specific scaling rule. As a consequence of the reduced dimensionality of the system, the scaling parameters appear to be insensitive to disorder.
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Affiliation(s)
- S V Andreev
- Laboratoire Charles Coulomb, Unité Mixte de Recherche 5221 CNRS/UM2, Université Montpellier 2, Place Eugne Bataillon, 34095 Montpellier Cedex, France
| | - A A Varlamov
- CNR-SPIN, Tor Vergata, Viale del Politecnico 1, I-00133 Rome, Italy
| | - A V Kavokin
- Physics and Astronomy School, University of Southampton, Highfield, Southampton SO171BJ, United Kingdom and Spin Optics Laboratory, State University of Saint Petersburg, 1, Ulianovskaya 198504, Russia
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14
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Andreev SV. Thermodynamic model of the macroscopically ordered exciton state. PHYSICAL REVIEW LETTERS 2013; 110:146401. [PMID: 25167012 DOI: 10.1103/physrevlett.110.146401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Indexed: 06/03/2023]
Abstract
We explain the experimentally observed instability of cold exciton gases and the formation of a macroscopically ordered exciton state in terms of a thermodynamic model accounting for the phase fluctuations of the condensate. We show that the temperature dependence of the exciton energy exhibits fundamental scaling behavior with the signature of the second order phase transition.
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Affiliation(s)
- S V Andreev
- Laboratoire Charles Coulomb, Unité Mixte de Recherche 5221 CNRS/UM2, Université Montpellier 2, Place Eugène Bataillon, 34095 Montpellier Cedex, France
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15
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Chernyuk AA, Sugakov VI, Tomylko VV. Exciton phase transitions in semiconductor quantum wells with disc-shaped electrode. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:195803. [PMID: 22517115 DOI: 10.1088/0953-8984/24/19/195803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Phase transitions in a system of indirect excitons in semiconductor double quantum wells are studied for a set-up when one of the electrodes is of finite size and, in particular, has the shape of a disc. At voltage a region under the rim of the disc is created where excitons have lower energy, thus providing a macroscopic trap attractive for excitons while being repulsive for charged particles. The theory of the formation of patterns of the excitonic condensed phase under the disc is built based on the assumption of the existence of the inter-exciton range where the interaction between them is attractive. The finite value of the exciton lifetime is taken into account serving as a limiting factor for the size of the islands of the condensed phase. The calculations reveal complex restructuring of the patterns of the spatial distribution of exciton density with increasing pumping intensity: from the structureless gaseous phase to separate islands of the condensed phase within the gaseous phase, then to islands of the gaseous phase in the bulk of the condensed phase and finally to the continuous condensed phase.
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Affiliation(s)
- A A Chernyuk
- Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, Ukraine
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16
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Shelykh IA, Taylor T, Kavokin AV. Rotons in a hybrid Bose-Fermi system. PHYSICAL REVIEW LETTERS 2010; 105:140402. [PMID: 21230816 DOI: 10.1103/physrevlett.105.140402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Revised: 08/10/2010] [Indexed: 05/30/2023]
Abstract
We calculate the spectrum of elementary excitations in a two-dimensional exciton condensate in the vicinity of a two-dimensional electron gas. We show that attraction of excitons due to their scattering with free electrons may lead to formation of a roton minimum. The energy of this minimum may go below the ground state energy which manifests breaking of the superfluidity. The Berezinsky-Kosterlitz-Thouless phase transition temperature decreases due to the exciton-exciton attraction mediated by electrons.
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Affiliation(s)
- Ivan A Shelykh
- Science Institute, University of Iceland, Dunhagi-3, IS-107, Reykjavik, Iceland
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17
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Dubi Y, Balatsky AV. Impurity-induced bound states and proximity effect in a bilayer exciton condensate. PHYSICAL REVIEW LETTERS 2010; 104:166802. [PMID: 20482072 DOI: 10.1103/physrevlett.104.166802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Indexed: 05/29/2023]
Abstract
The effect of impurities which induce local interlayer tunneling in bilayer exciton condensates is discussed. We show that a localized single-fermion bound state emerges inside the gap for any strength of impurity scattering and calculate the dependence of the impurity state energy and wave function on the potential strength. We show that such an impurity-induced single-fermion state enhances the interlayer coherence around it, and is similar to the superconducting proximity effect. As a direct consequence of these single-impurity states, we predict that a finite concentration of such impurities will increase the critical temperature for exciton condensation.
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Affiliation(s)
- Yonatan Dubi
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Dolcini F, Rainis D, Taddei F, Polini M, Fazio R, Macdonald AH. Blockade and counterflow supercurrent in exciton-condensate Josephson junctions. PHYSICAL REVIEW LETTERS 2010; 104:027004. [PMID: 20366620 DOI: 10.1103/physrevlett.104.027004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2009] [Indexed: 05/29/2023]
Abstract
We demonstrate that perfect conversion between charged supercurrents in superconductors and neutral supercurrents in electron-hole pair condensates is possible via a new Andreev-like scattering mechanism. As a result, when two superconducting circuits are coupled through a bilayer exciton condensate, the superflow in both layers is drastically modified. Depending on the phase biases the supercurrents can be completely blocked or exhibit perfect drag.
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Ali Can M, Hakioğlu T. Unconventional pairing in excitonic condensates under spin-orbit coupling. PHYSICAL REVIEW LETTERS 2009; 103:086404. [PMID: 19792744 DOI: 10.1103/physrevlett.103.086404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 07/22/2009] [Indexed: 05/28/2023]
Abstract
It is shown that Rashba and Dresselhaus spin-orbit couplings enhance the conclusive power in the experiments on the excitonic condensate by at least three low temperature effects. First, spin-orbit coupling facilitates the photoluminescence measurements via enhancing the bright contribution in the otherwise dominantly dark ground state. The second is the presence of a low temperature power law dependence of the specific heat and weakening of the second order transition at the critical temperature. The third is the appearance of the nondiagonal elements in the static spin susceptibility.
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Affiliation(s)
- M Ali Can
- Department of Physics, Bilkent University, 06800 Ankara, Turkey
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20
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Sonin EB. Gauge-field rotation of an electrically polarized bose condensate by a radial magnetic field. PHYSICAL REVIEW LETTERS 2009; 102:106407. [PMID: 19392139 DOI: 10.1103/physrevlett.102.106407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2008] [Indexed: 05/27/2023]
Abstract
Here it is shown that a condensate of electrically polarized bosons subject to a radial magnetic field must rotate due to the Aharonov-Bohm effect. As in mechanically rotated superfluids, rotation is accompanied by penetration of vortices into the condensate at some critical magnetic field. In the case of a Bose-condensed exciton cloud in a double-quantum well, a necessary electric polarization is provided with spatial separation of electrons and holes forming excitons. Penetration of vortices strongly affects the intensity and the angular distribution of photoluminescence from the exciton cloud. This effect can be used for an experimental manifestation of exciton Bose condensation.
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Affiliation(s)
- E B Sonin
- Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel
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Fischer AM, Campo VL, Portnoi ME, Römer RA. Exciton storage in a nanoscale Aharonov-Bohm ring with electric field tuning. PHYSICAL REVIEW LETTERS 2009; 102:096405. [PMID: 19392542 DOI: 10.1103/physrevlett.102.096405] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Indexed: 05/27/2023]
Abstract
We study analytically the optical properties of a simple model for an electron-hole pair on a ring subjected to perpendicular magnetic flux and in-plane electric field. We show how to tune this excitonic system from optically active to optically dark as a function of these external fields. Our results offer a simple mechanism for exciton storage and readout.
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Affiliation(s)
- Andrea M Fischer
- Department of Physics and Centre for Scientific Computing, University of Warwick, Coventry, CV4 7AL, United Kingdom
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Wouters M, Carusotto I. Excitations in a nonequilibrium Bose-Einstein condensate of exciton polaritons. PHYSICAL REVIEW LETTERS 2007; 99:140402. [PMID: 17930649 DOI: 10.1103/physrevlett.99.140402] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2007] [Indexed: 05/25/2023]
Abstract
We develop a mean-field theory of the dynamics of a nonequilibrium Bose-Einstein condensate of exciton polaritons in a semiconductor microcavity. The spectrum of elementary excitations around the stationary state is analytically studied by means of a generalized Gross-Pitaevskii equation. A diffusive behavior of the Goldstone mode is found in the spatially homogeneous case and new features are predicted for the Josephson effect in a two-well geometry.
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Affiliation(s)
- Michiel Wouters
- TFVS, Universiteit Antwerpen, Groenenborgerlaan 171, 2020, Antwerpen, Belgium
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