Nonlinear conductivity in CaRuO3 thin films measured by short current pulses

Metals near quantum critical points have been predicted to display universal out-of-equilibrium behaviour in the steady current-carrying state. We have studied the nonlinear conductivity of high-quality CaRuO3 thin films with residual resistivity ratios up to 57 using microsecond-short, high-field current pulses at low temperatures. Even for our shortest pulses, Joule heating persists, making it impossible to observe an intrinsic nonlinearity. Comparing with THz spectroscopic results, we can establish a clear window for the pulse duration needed to observe the predicted universal nonlinear conductivity.