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

TL;DR

This paper models the creation of electron-hole pairs in graphene under electric fields, revealing a transition from linear to nonlinear behavior, and draws parallels to quantum electrodynamics phenomena like Schwinger pair production.

Contribution

It provides a quantitative, dynamic first-quantized analysis of pair creation, nonlinear conductivity, and the chiral anomaly effects in graphene under strong electric fields.

Findings

Linear response characterized by universal minimal resistivity.

Rapid growth of conductivity beyond a certain time scale.

Electron-hole plasma formation analogous to Schwinger pair creation.

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 $t_{nl}\propto E^{-1/2}$ the physical behaviour 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.