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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