Anomalous Landau level gaps near magnetic transitions in monolayer WSe_2
arxiv(2024)
摘要
First-order phase transitions produce abrupt changes to the character of both
ground and excited electronic states. Here we conduct electronic
compressibility measurements to map the spin phase diagram and Landau level
(LL) energies of monolayer WSe_2 in a magnetic field. We resolve a sequence
of first-order phase transitions between completely spin-polarized LLs and
states with LLs of both spins. Unexpectedly, the LL gaps are roughly constant
over a wide range of magnetic fields below the transitions, which we show
reflects a preference for opposite spin excitations of the spin-polarized
ground state. These transitions also extend into compressible regimes, with a
sawtooth boundary between full and partial spin polarization. We link these
observations to the important influence of LL filling on the exchange energy
beyond a smooth density-dependent contribution. Our results show that WSe_2
realizes a unique hierarchy of energy scales where such effects induce
re-entrant magnetic phase transitions tuned by density and magnetic field.
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