Two parameter flow of \sigma_{xx}(\omega) - \sigma_{xy}(\omega) for the   graphene quantum Hall system in ac regime
  Flow diagram of $(\sigma_{xx}, \sigma_{xy})$ in finite-frequency ($\omega$) regime is numerically studied for graphene quantum Hall effect (QHE) system. The ac flow diagrams turn out to show qualitatively similar behavior as the dc flow diagrams, which can be understood that the dynamical length scale determined by the frequency poses a relevant cutoff for the renormalization flow. Then the two parameter flow is discussed in terms of the dynamical scaling theory. We also discuss the larger-$\omega$ regime which exhibits classical flows driven by the raw frequency $\omega$. 
Takahiro Morimoto, Hideo Aoki
cond-mat.mes-hall