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.

8 pages, 4 figures + 3 supplementary figures

References in corpus (6)

• Magnetic Control of Valley Pseudospin in Monolayer WSe2
• Quantum Hall Ferromagnetism in Graphene
• Valley susceptibility of an interacting two-dimensional electron system
• Many-Body Theory of Trion Absorption Features in Two-Dimensional Semiconductors
• Valley-spin polarized Landau levels in a monolayer semiconductor
• Landau-quantized excitonic absorption and luminescence in a monolayer valley semiconductor

Cited by in corpus (4)

• Valley relaxation of resident electrons and holes in a monolayer semiconductor: Dependence on carrier density and the role of substrate-induced disorder
• Many-body exciton and inter-valley correlations in heavily electron-doped WSe${}_2$ monolayers
• Robust Quantum Hall Ferromagnetism near a Gate-Tuned ν = 1 Landau Level Crossing
• Giant and Broadband Circular Dichroism from Particle-Hole Symmetry Breaking in Weyl Semimetals