Anomalous Landau level gaps near magnetic transitions in monolayer WSe${}_2$

Abstract

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.

References in corpus (13)

• Quantum Hall Ferromagnetism in Graphene
• Cascade of Phase Transitions and Dirac Revivals in Magic Angle Graphene
• Valley susceptibility of an interacting two-dimensional electron system
• Valley-spin polarized Landau levels in a monolayer semiconductor
• Programming Correlated Magnetic States via Gate Controlled Moiré Geometry
• Mapping twist-tuned multiband topology in bilayer WSe${}_2$
• Correlated Hofstadter Spectrum and Flavor Phase Diagram in Magic Angle Graphene
• Odd- and even-denominator fractional quantum Hall states in monolayer WSe${}_2$
• Bilayer WSe${}_2$ as a natural platform for interlayer exciton condensates in the strong coupling limit
• Tunable spin and valley excitations of correlated insulators in $\Gamma$-valley moiré bands
• Polarization dependent Landau level crossing in a two-dimensional electron system in MgZnO/ZnO-heterostructure
• Spontaneous valley polarization of interacting carriers in a monolayer semiconductor
• Hofstadter states and reentrant charge order in a semiconductor moiré lattice