Spontaneous valley polarization of interacting carriers in a monolayer semiconductor

Abstract

We report magneto-absorption spectroscopy of gated WSe${}_2$ 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 ${\sigma }^{\pm }$ circular polarizations, which unambiguously and separately indicate the number of filled Landau levels (LLs) in both $K$ and $K^{\prime }$ 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 $K^{\prime }$, 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.

arXiv comment8 pages, 4 figures + 3 supplementary figures

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Cited by in corpus (14)

• Magnetooptics of layered two-dimensional semiconductors and heterostructures: progress and prospects
• Valley relaxation of resident electrons and holes in a monolayer semiconductor: Dependence on carrier density and the role of substrate-induced disorder
• Controlling exciton many-body states by the electric-field effect in monolayer MoS${}_2$
• Many-body exciton and inter-valley correlations in heavily electron-doped WSe${}_2$ monolayers
• Mott-moiré excitons
• Robust Quantum Hall Ferromagnetism near a Gate-Tuned ν = 1 Landau Level Crossing
• Valley-Filling Instability and Critical Magnetic Field for Interaction-Enhanced Zeeman Response in Doped WSe${}_2$ Monolayers
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• Anomalous Landau level gaps near magnetic transitions in monolayer WSe${}_2$
• Two-dimensional bound excitons in real space and Landau quantization space: A comparative study