Charging effects observed in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ films: Influence of oxygen ordering

The chain oxygen dynamics of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ have been investigated using a Monte Carlo simulation of the asymmetric next-nearest-neighbor Ising model for the oxygen atoms in the basal plane. The effect of an externally applied electric field is shown to change the basal plane coordination of Cu ions, resulting in a change in the carrier doping of the ${\mathrm{CuO}}_2$ planes. Good quantitative agreement is obtained with the asymmetry observed in field effect experiments. We present results under different applied external fields, study the long-term ordering dynamics and investigate the effect of oxygen content on the phenomenon. We discuss the relevance of our results to studies of point-contact spectroscopy, tunneling, electromigration, and the enhancement of superconductivity by photoexcitation. We also present a historical perspective in terms of the Verwey transition in ${\mathrm{Fe}}_3$ ${\mathrm{O}}_4$, which involves a similar mechanism.