arXiv:1101.2283 · Physical Review B
Crossover from bias-induced to field-induced breakdown in one-dimensional band and Mott insulators attached to electrodes
Yasuhiro Tanaka, Kenji Yonemitsu
Abstract
Nonequilibrium states induced by an applied bias voltage $(V)$ and the corresponding current-voltage characteristics of one-dimensional models describing band and Mott insulators are investigated theoretically by using nonequilibrium Green's functions. We attach the models to metallic electrodes, the effects of which are incorporated into the self-energy. Modulation of the electron density and the scalar potential coming from the additional long-range interaction are calculated self-consistently within the Hartree approximation. For both models of band and Mott insulators with length ${L}_{C}$, the bias voltage induces a breakdown of the insulating state, the threshold of which shows a crossover depending on ${L}_{C}$. It is determined basically by the bias ${V}_{\mathrm{th}}~\ensuremath{\Delta}$ for ${L}_{C}$ smaller than the correlation length $\ensuremath{\xi}=W/\ensuremath{\Delta}$, where $W$ denotes the bandwidth and $\ensuremath{\Delta}$ denotes the energy gap. For systems with ${L}_{C}\ensuremath{\gg}\ensuremath{\xi}$, the threshold is governed by the electric field ${V}_{\mathrm{th}}/{L}_{C}$, which is consistent with a Landau-Zener--type breakdown ${V}_{\mathrm{th}}/{L}_{C}\ensuremath{\propto}{\ensuremath{\Delta}}^{2}/W$. We demonstrate that the spatial dependence of the scalar potential is crucially important for this crossover by showing the case without the scalar potential, where the breakdown occurs at ${V}_{\mathrm{th}}~\ensuremath{\Delta}$ regardless of the length ${L}_{C}$.