Spontaneous Valley Polarization of Interacting Carriers in a Monolayer Semiconductor

We report magnetoabsorption spectroscopy of gated WSe2 monolayers in high magnetic fields up to 60 T. When doped with a 2D Fermi sea of mobile holes, well-resolved sequences of optical transitions are observed in both σ± circular polarizations, which unambiguously and separately indicate the number...

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Bibliographic Details
Published in:Physical review letters 2020-10, Vol.125 (14), p.1-147602, Article 147602
Main Authors: Li, J., Goryca, M., Wilson, N. P., Stier, A. V., Xu, X., Crooker, S. A.
Format: Article
Language:English
Subjects:
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
exchange interaction
Hole density
Monolayers
optical spectroscopy
transition-metal dichalcogenide
two-dimensional electron system
Valleys
valleytronics
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Summary:We report magnetoabsorption spectroscopy of gated WSe2 monolayers in high magnetic fields up to 60 T. When doped with a 2D Fermi sea of mobile holes, well-resolved sequences of optical transitions are observed in both σ± circular polarizations, which unambiguously and separately indicate the number of filled Landau levels (LLs) in both K and K ′ valleys. This reveals the interaction-enhanced valley Zeeman energy, which is found to be highly tunable with hole density p . We exploit this tunability to align the LLs in K and K ′ , and find that the 2D hole gas becomes unstable against small changes in LL filling and can spontaneously valley polarize. These results cannot be understood within a single-particle picture, highlighting the importance of exchange interactions in determining the ground state of 2D carriers in monolayer semiconductors.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.125.147602