Destabilizing Mott insulators with currents: theory and application to Ca$_2$RuO$_4$

Nakamura, Maeno et al. (Scientific Reports, 2013) showed that under an electric field ($\sim40\,\rm{V/cm}$), the metal insulator transition temperature decreases, so that $\rm{Ca_2RuO_4}$ remains metallic at temperatures well below the equilibrium transition temperature. They further showed that this phenomenon is not due to the Joule heating, and argued that it arose from a nonequilibrium correlation effect. In this work we investigate the issue theoretically, using a one dimensional density wave model and considering Zener tunnelling and in-band and interband relaxation processes. Boltzmann-type transport equations are derived for conduction and valence band, including photon (up to quadratic order) and phonon relaxation terms. Even for modest fields a substantial population imbalance may be induced and consequently destabilize the gap. This work is supported by the NSF DMR 1308236 grant.