Unusual microwave response of dirac quasiparticles in graphene

Abstract

Recent experiments have proven that the quasiparticles in graphene obey a Dirac equation. Here we show that microwaves are an excellent probe of their unusual dynamics. When the chemical potential is small, the intraband response can exhibit a cusp around zero frequency Ω and this unusual line shape changes to Drude-like by increasing the chemical potential |μ|, with width linear in μ. The interband contribution at T=0 is a constant independent of Ω with a lower cutoff at 2μ. Distinctly different behavior occurs if interaction-induced phenomena in graphene cause an opening of a gap Δ. At a large magnetic field B, the diagonal and Hall conductivities at small Ω become independent of B but remain nonzero and show a structure associated with the lowest Landau level. This occurs because in the Dirac theory the energy of this level, E0=±Δ, is field independent in sharp contrast to the conventional case. © 2006 The American Physical Society.