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Zheng H, Wu B, Li S, He J, Liu Z, Wang CT, Wang JT, Duan JA, Liu Y. Strain-tunable valley polarization and localized excitons in monolayer WSe 2. OPTICS LETTERS 2023; 48:2393-2396. [PMID: 37126281 DOI: 10.1364/ol.487201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Monolayer transition metal dichalcogenides (TMDs) have a crystalline structure with broken spatial inversion symmetry, making them promising candidates for valleytronic applications. However, the degree of valley polarization is usually not high due to the presence of intervalley scattering. Here, we use the nanoindentation technique to fabricate strained structures of WSe2 on Au arrays, thus demonstrating the generation and detection of strained localized excitons in monolayer WSe2. Enhanced emission of strain-localized excitons was observed as two sharp photoluminescence (PL) peaks measured using low-temperature PL spectroscopy. We attribute these emerging sharp peaks to excitons trapped in potential wells formed by local strains. Furthermore, the valley polarization of monolayer WSe2 is modulated by a magnetic field, and the valley polarization of strained localized excitons is increased, with a high value of up to approximately 79.6%. Our results show that tunable valley polarization and localized excitons can be realized in WSe2 monolayers, which may be useful for valleytronic applications.
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Shanks DN, Mahdikhanysarvejahany F, Stanfill TG, Koehler MR, Mandrus DG, Taniguchi T, Watanabe K, LeRoy BJ, Schaibley JR. Interlayer Exciton Diode and Transistor. NANO LETTERS 2022; 22:6599-6605. [PMID: 35969812 DOI: 10.1021/acs.nanolett.2c01905] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Controlling the flow of charge neutral interlayer exciton (IX) quasiparticles can potentially lead to low loss excitonic circuits. Here, we report unidirectional transport of IXs along nanoscale electrostatically defined channels in an MoSe2-WSe2 heterostructure. These results are enabled by a lithographically defined triangular etch in a graphene gate to create a potential energy "slide". By performing spatially and temporally resolved photoluminescence measurements, we measure smoothly varying IX energy along the structure and high speed exciton flow with a drift velocity up to 2 × 106 cm/s, an order of magnitude larger than previous experiments. Furthermore, exciton flow can be controlled by saturating exciton population in the channel using a second laser pulse, demonstrating an optically gated excitonic transistor. Our work paves the way toward low loss excitonic circuits, the study of bosonic transport in one-dimensional channels, and custom potential energy landscapes for excitons in van der Waals heterostructures.
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Affiliation(s)
- Daniel N Shanks
- Department of Physics, University of Arizona, Tucson, Arizona 85721, United States
| | | | - Trevor G Stanfill
- Department of Physics, University of Arizona, Tucson, Arizona 85721, United States
| | - Michael R Koehler
- IAMM Diffraction Facility, Institute for Advanced Materials and Manufacturing, University of Tennessee, Knoxville, Tennessee 37920, United States
| | - David G Mandrus
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Brian J LeRoy
- Department of Physics, University of Arizona, Tucson, Arizona 85721, United States
| | - John R Schaibley
- Department of Physics, University of Arizona, Tucson, Arizona 85721, United States
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Lagoin C, Suffit S, West K, Baldwin K, Pfeiffer L, Holzmann M, Dubin F. Quasicondensation of Bilayer Excitons in a Periodic Potential. PHYSICAL REVIEW LETTERS 2021; 126:067404. [PMID: 33635707 DOI: 10.1103/physrevlett.126.067404] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 01/14/2021] [Indexed: 06/12/2023]
Abstract
We study two-dimensional excitons confined in a lattice potential, for high fillings of the lattice sites. We show that a quasicondensate is possibly formed for small values of the lattice depth, but for larger ones the critical phase-space density for quasicondensation rapidly exceeds our experimental reach, due to an increase of the exciton effective mass. On the other hand, in the regime of a deep lattice potential where excitons are strongly localized at the lattice sites, we show that an array of phase-independent quasicondensates, different from a Mott insulator, is realized.
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Affiliation(s)
- Camille Lagoin
- Institut des Nanosciences de Paris, CNRS and Sorbonne Université, 4 pl. Jussieu, 75005 Paris, France
| | - Stephan Suffit
- Laboratoire de Materiaux et Phenomenes Quantiques, Universite Paris Diderot, 75013 Paris, France
| | - Kenneth West
- PRISM, Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08540, USA
| | - Kirk Baldwin
- PRISM, Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08540, USA
| | - Loren Pfeiffer
- PRISM, Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08540, USA
| | | | - François Dubin
- Institut des Nanosciences de Paris, CNRS and Sorbonne Université, 4 pl. Jussieu, 75005 Paris, France
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