Interaction-induced shift of the cyclotron resonance of graphene using infrared spectroscopy

TL;DR

This study reveals that electron interactions in graphene cause significant, non-monotonic shifts in cyclotron resonance energies at the n=0 Landau level, indicating an interaction-induced energy gap at high magnetic fields.

Contribution

It demonstrates that interaction effects in graphene lead to a large, filling-factor-dependent shift in cyclotron resonance, challenging the applicability of Kohn's theorem.

Findings

CR transition energy shifts up to 10% at half-filling

Interaction-enhanced energy gap observed at high magnetic fields

Non-monotonic dependence of CR energy on filling factor

Abstract

We report a study of the cyclotron resonance (CR) transitions to and from the unusual $n=0$ Landau level (LL) in monolayer graphene. Unexpectedly, we find the CR transition energy exhibits large (up to 10%) and non-monotonic shifts as a function of the LL filling factor, with the energy being largest at half-filling of the $n=0$ level. The magnitude of these shifts, and their magnetic field dependence, suggests that an interaction-enhanced energy gap opens in the $n=0$ level at high magnetic fields. Such interaction effects normally have limited impact on the CR due to Kohn's theorem [W. Kohn, Phys. Rev. {\bf 123}, 1242 (1961)], which does not apply in graphene as a consequence of the underlying linear band structure.