Space-time dispersion of graphene conductivity
  We present an analytic calculation of the conductivity of pure graphene as a function of frequency $\omega $, wave-vector $k$, and temperature for the range where the energies related to all these parameters are small in comparison with the band parameter $\gamma =3$ eV. The simple asymptotic expressions are given in various limiting cases. For instance, the conductivity for $kv_{0}\ll T\ll \omega $ is equal to $\sigma (\omega, k)=e^{2}/4\hbar $ and independent of the band structure parameters $\gamma $ and $v_{0}$. Our results are also used to explain the known dependence of the graphite conductivity on temperature and pressure. 
L. A. Falkovsky, A. A. Varlamov