Spin-flip excitations, spin waves, and magneto-excitons in graphene Landau levels at integer filling factors

TL;DR

This paper investigates collective electronic excitations in graphene under strong magnetic fields, focusing on spin-flip and spin-wave modes, and discusses their theoretical descriptions and implications for quantum Hall physics.

Contribution

It provides a detailed analysis of spin-related excitations in graphene's quantum Hall regime, highlighting differences from conventional systems and evaluating the applicability of key theorems.

Findings

Spin-flip and spin-wave excitations are well described by time-dependent Hartree-Fock.

Spin-conserving modes involve significant Landau-level mixing at finite wave vectors.

Kohn's theorem does not hold for relativistic electrons in graphene.

Abstract

We study collective electronic excitations in graphene in the integer quantum Hall regime, concentrating mainly on excitations with spin reversal such as spin-flip and spin-wave excitations. We show that these excitations are correctly accounted for in the time-dependent Hartree-Fock and strong magnetic field approximations, in contrast to spin-conserving (magneto-exciton) modes which involve a strong Landau-level mixing at non-zero wave vectors. The collective excitations are discussed in view of prominent theorems, such as Kohn's and Larmor's. Whereas the latter remains valid in graphene and yields insight into the understanding of spin-dependent modes, Kohn's theorem does not apply to relativistic electrons in graphene. We finally calculate the exchange correction to the chemical potential in the weak magnetic field limit.