Valley-selective optical Stark effect in monolayer WS[subscript 2]
Author(s)McIver, James; Lee, Yi-Hsien; Fu, Liang; Kong, Jing; Gedik, Nuh; Sie, Edbert Jarvis; ... Show more Show less
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Breaking space–time symmetries in two-dimensional crystals can markedly influence their macroscopic electronic properties. Monolayer transition metal dichalcogenides (TMDs) are prime examples where the intrinsically broken crystal inversion symmetry permits the generation of valley-selective electron populations, even though the two valleys are energetically degenerate, locked by time-reversal symmetry. Lifting the valley degeneracy in these materials is of great interest because it would allow for valley-specific band engineering and offer additional control in valleytronic applications. Although applying a magnetic field should, in principle, accomplish this task, experiments so far have not shown valley-selective energy level shifts in fields accessible in the laboratory. Here, we show the first direct evidence of lifted valley degeneracy in the monolayer TMD WS[subscript 2]. By applying intense circularly polarized light, which breaks time-reversal symmetry, we demonstrate that the exciton level in each valley can be selectively tuned by as much as 18 meV through the optical Stark effect. These results offer a new way to control the valley degree of freedom, and may provide a means to realize new Floquet topological phases in two-dimensional TMDs.
DepartmentMassachusetts Institute of Technology. Department of Electrical Engineering and Computer Science; Massachusetts Institute of Technology. Department of Physics
Nature Publishing Group
Sie, Edbert J., James W. McIver, Yi-Hsien Lee, Liang Fu, Jing Kong, and Nuh Gedik. “Valley-Selective Optical Stark Effect in Monolayer WS[subscript 2].” Nat Mater 14, no. 3 (December 15, 2014): 290–294.
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