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Scrace T, Tsai Y, Barman B, Schweidenback L, Petrou A, Kioseoglou G, Ozfidan I, Korkusinski M, Hawrylak P. Magnetoluminescence and valley polarized state of a two-dimensional electron gas in WS2 monolayers. NATURE NANOTECHNOLOGY 2015; 10:603-7. [PMID: 25961511 DOI: 10.1038/nnano.2015.78] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Accepted: 03/16/2015] [Indexed: 05/09/2023]
Abstract
Materials often exhibit fundamentally new phenomena in reduced dimensions that potentially lead to novel applications. This is true for single-layer, two-dimensional semiconductor crystals of transition-metal dichalcogenides, MX2 (M = Mo, W and X = S, Se). They exhibit direct bandgaps with energies in the visible region at the two non-equivalent valleys in the Brillouin zone. This makes them suitable for optoelectronic applications that range from light-emitting diodes to light harvesting and light sensors, and to valleytronics. Here, we report the results of a magnetoluminescence study of WS2 single-layer crystals in which the strong spin-orbit interaction additionally locks the valley and spin degrees of freedom. The recombination of the negatively charged exciton in the presence of a two-dimensional electron gas (2DEG) is found to be circularly polarized at zero magnetic field despite being excited with unpolarized light, which indicates that the existence of a valley polarized 2DEG is caused by valley and spin locking and strong electron-electron interactions.
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Affiliation(s)
- T Scrace
- University at Buffalo, SUNY, Buffalo, New York 14260, USA
| | - Y Tsai
- University at Buffalo, SUNY, Buffalo, New York 14260, USA
| | - B Barman
- University at Buffalo, SUNY, Buffalo, New York 14260, USA
| | | | - A Petrou
- University at Buffalo, SUNY, Buffalo, New York 14260, USA
| | | | - I Ozfidan
- 1] Quantum Theory Group, Emerging Technologies Division, National Research Council, Ottawa K1A 0R6, Ontario, Canada [2] Department of Physics, University of Ottawa, Ottawa K1N 6N5, Ontario, Canada
| | - M Korkusinski
- Quantum Theory Group, Emerging Technologies Division, National Research Council, Ottawa K1A 0R6, Ontario, Canada
| | - P Hawrylak
- 1] Quantum Theory Group, Emerging Technologies Division, National Research Council, Ottawa K1A 0R6, Ontario, Canada [2] Department of Physics, University of Ottawa, Ottawa K1N 6N5, Ontario, Canada
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Teneh N, Kuntsevich AY, Pudalov VM, Reznikov M. Spin-droplet state of an interacting 2D electron system. PHYSICAL REVIEW LETTERS 2012; 109:226403. [PMID: 23368139 DOI: 10.1103/physrevlett.109.226403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Indexed: 06/01/2023]
Abstract
We report thermodynamic magnetization measurements of two-dimensional electrons in several high-mobility Si metal-oxide-semiconductor field-effect transistors. We provide evidence for an easily polarizable electron state in a wide density range from insulating to deep into the metallic phase. The temperature and magnetic field dependence of the magnetization is consistent with the formation of large-spin droplets in the insulating phase. These droplets melt in the metallic phase with increasing density and temperature, though they survive up to large densities.
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Affiliation(s)
- N Teneh
- Solid State Institute, Technion, Haifa 32000, Israel
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Goswami S, Siegert C, Baenninger M, Pepper M, Farrer I, Ritchie DA, Ghosh A. Highly enhanced thermopower in two-dimensional electron systems at millikelvin temperatures. PHYSICAL REVIEW LETTERS 2009; 103:026602. [PMID: 19659228 DOI: 10.1103/physrevlett.103.026602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Indexed: 05/28/2023]
Abstract
We report experimental observation of an unexpectedly large thermopower in mesoscopic two-dimensional (2D) electron systems in GaAs/AlGaAs heterostructures at sub-Kelvin temperatures and zero magnetic field. Unlike conventional nonmagnetic high-mobility 2D systems, the thermopower in our devices increases with decreasing temperature below 0.3 K, reaching values in excess of 100 microV/K, thus exceeding the free electron estimate by more than 2 orders of magnitude. With support from a parallel study of the local density of states, we suggest such a phenomenon to be linked to intrinsic localized states and many-body spin correlations in the system.
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Affiliation(s)
- Srijit Goswami
- Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
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Drummond ND, Needs RJ. Phase diagram of the low-density two-dimensional homogeneous electron gas. PHYSICAL REVIEW LETTERS 2009; 102:126402. [PMID: 19392300 DOI: 10.1103/physrevlett.102.126402] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Indexed: 05/27/2023]
Abstract
We use quantum Monte Carlo methods to calculate the zero-temperature phase diagram of the two-dimensional homogeneous electron gas. We find a transition from a paramagnetic fluid to an antiferromagnetic triangular Wigner crystal at density parameter r(s)=31(1) a.u. and a transition to a ferromagnetic crystal at r(s)=38(5) a.u. The fully spin-polarized fluid is never stable. We search for, but do not find, the ferromagnetic "hybrid" phase proposed by H. Falakshahi and X. Waintal [Phys. Rev. Lett. 94, 046801 (2005)10.1103/PhysRevLett.94.046801].
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Ghosh A, Wright MH, Siegert C, Pepper M, Farrer I, Ford CJB, Ritchie DA. Zero-bias anomaly and kondo-assisted quasiballistic 2D transport. PHYSICAL REVIEW LETTERS 2005; 95:066603. [PMID: 16090970 DOI: 10.1103/physrevlett.95.066603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2004] [Revised: 04/18/2005] [Indexed: 05/03/2023]
Abstract
Nonequilibrium transport measurements in mesoscopic quasiballistic 2D electron systems show an enhancement in the differential conductance around the Fermi energy. At very low temperatures, such a zero-bias anomaly splits, leading to a suppression of linear transport at low energies. We also observed a scaling of the nonequilibrium characteristics at low energies which resembles electron scattering by two-state systems, addressed in the framework of two-channel Kondo model. Detailed sample-to-sample reproducibility indicates an intrinsic phenomenon in unconfined 2D systems in the low electron-density regime.
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Affiliation(s)
- A Ghosh
- Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, United Kingdom
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Ovchinnikov IV, Neuhauser D. Finite bias conductance of an Anderson level: A source-Liouville Hartree–Fock study. J Chem Phys 2005; 122:54106. [PMID: 15740309 DOI: 10.1063/1.1835261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We address the problem of stationary conductance through an Anderson spin-degenerate level at finite bias. Just as in the Anderson solution, for a finite bias in parameter space (bias, gate voltage, interaction constant, and the couplings to the leads) there exist spin-polarized and non-spin-polarized regions. The transition curve between them is found analytically for the case of symmetric coupling to the left and right leads. We approach the problem by a non-Markovian source-Liouville equation where the two-body interaction self-energies are taken in the Hartree-Fock approximation.
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Affiliation(s)
- Igor V Ovchinnikov
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA
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