Broken symmetries and Kohn's theorem in graphene cyclotron resonance

Abstract

The magnetoplasmon spectrum of Landau level transitions in hexagonal boron nitrideencapsulated 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.

Many-body effects, orbital mixing, and cyclotron resonance in bilayer graphene

“…Recently, Russell et al [35] have reported a direct signal of manybody effects on CR in high-mobility hBN-encapsulated monolayer graphene; see also ref. [36]. They observed significant variations of resonance energies over a finite range of filling factor ν under a fixed magnetic field B; the point lies in extracting genuine Coulombic effects as a function of ν while controlling the running of the velocity factor with B.…”