Ballistic transport, chiral anomaly, and emergence of the neutral electron-hole plasma in graphene

Abstract

The process of coherent creation of particle-hole excitations by an electric field in graphene is quantitatively described using a dynamic "first-quantized" approach. We calculate the evolution of current density, number of pairs, and energy in ballistic regime using the tight-binding model. The series in electric field strength E up to third order in both dc and ac are calculated. We show how the physics far from the two Dirac points enters various physical quantities in linear response and how it is related to the chiral anomaly. The third harmonic generation and the imaginary part of conductivity are obtained. It is shown that at certain time scale t(nl) alpha E-1/2 the physical behavior dramatically changes and the perturbation theory breaks down. Beyond the linear-response physics is explored using an exact solution of the first-quantized equations. While for small electric fields the I-V curve is linear characterized by the universal minimal resistivity sigma=pi/2(e(2)/h), at t>t(nl) the conductivity grows fast. The copious pair creation (with rate E-3/2), analogous to Schwinger's electron-positron pair creation from vacuum in QED, leads to creation of the electron-hole plasma at ballistic times of order t(nl). This process is terminated by a relaxational recombination.