Low temperature high bias enhanced noise in atomic-scale Au junctions*

We report measurements on STM-style Au break junctions, investigating the bias dependence of current noise at room temperature, 77K, and 4K. Previous experiments at room temperature observed that low bias noise (\textless 150mV) agrees well with predictions for shot noise at fixed electronic temperature, but at high biases, noise was found to have a nonlinear dependence on the scaled bias. Possible sources of this deviation are nonequilibrium electron-phonon effects or local heating of the electronic distribution. In order to expand upon the understanding of the enhanced noise at high bias, we have measured current noise for a range of biases as a function of environmental temperature. This allows for distinction between electron-electron and electron-vibrational contributions to the shot noise. We will discuss differences in the bias dependence of the noise between cryogenic and room temperature conditions.