Abstract
The magnetoplasmon spectrum of Landau level transitions in hexagonal boron nitride-encapsulated graphene is explored via infrared transmission magnetospectroscopy, as a function of the filling factor at fixed magnetic field. As the lowest Landau level occupancy is increased from half-filling, a non-monotonic progression of multiple cyclotron resonance peaks is observed, with a single peak evolving into four peaks and back to two, all with linewidths of order 0.5 meV. This provides a novel window on the interplay of electron interactions with broken spin and valley symmetries in the quantum Hall regime. Analysis of the peak energies shows an indirect enhancement of spin gaps below the Fermi energy, a Dirac mass at half-filling that is nearly 50\% larger than when the lowest Landau level is completely full, and a small but clear particle-hole asymmetry. We suggest a key role is played by the boron nitride in enabling interaction-enhanced broken symmetries to be observed in graphene cyclotron resonance.
Highlights
In graphene, Coulomb interactions combine with spin and valley degrees of freedom to generate an approximate SU(4) symmetry, which when broken can give rise to novel magnetic ground states in the quantum Hall regime at high magnetic fields
As the occupancy of the zeroth Landau level is increased from half-filling, a nonmonotonic progression of multiple cyclotron resonance peaks is seen for several interband transitions, revealing the evolution of underlying many-particle-enhanced gaps
Graphene is an ideal platform in which to pursue such studies because, in contrast to traditional two-dimensional electron systems having a parabolic dispersion, the linear dispersion of graphene allows the contribution of many-particle interactions to directly modify the LL transition energies in measurements of the cyclotron resonance (CR)
Summary
Coulomb interactions combine with spin and valley degrees of freedom to generate an approximate SU(4) symmetry, which when broken can give rise to novel magnetic ground states in the quantum Hall regime at high magnetic fields. These phenomena have been explored by a variety of experimental probes, including electronic transport, quantum capacitance, and scanning probe microscopy experiments [1,2,3,4,5,6,7].
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