Abstract

The vanishing energy scales near to a quantum critical point leave a system susceptible to being driven out of thermal equilibrium by external probes, when the energy scale of the probe scale exceeds the temperature. Usually, non-equilibrium distributions are not universal. However, when a quantum critical system is driven into a non-equilibrium steady state, it may show universal behaviour. The form of a non-equilibrium steady state is largely determined by dynamics. The quantum critical state exhibits universality in temporal as well as spatial correlation. This universality in dynamics, then may reveal itself in the form of the non-equilibrium distribution. We show as a result that the universal, power-law temperature dependence in resistivity of an itinerant-electron quantum critical magnet may be reflected in a universal non-linear conductivity ; when a strong electric field is applied, the resulting current has a universal power-law dependence upon the applied electric field.