Single-particle relaxation time versus scattering time in 2D graphene layers

We calculate the transport scattering time ($\tau_t$) and the single particle relaxation time ($\tau_s$) for disordered graphene in the lowest order of the electron-impurity interaction (Born approximation). We find that the ratio of $\tau_t$ to $\tau_s$ is always greater (less) than two for charged Coulomb (short-ranged neutral) scatterers. Thus, the calculated scattering time ratio can be a good criterion of directly selecting the dominant scattering mechanism in graphene. As a direct consequence of scattering times we calculate graphene mobility, damping rate, and density of states of single particle state.