Enhanced noise at high bias in atomic-scale Au break junctions

TL;DR

This study investigates bias-induced noise in atomic-scale gold break junctions, revealing nonlinear noise behavior at high bias and exploring potential mechanisms beyond ionic heating, with implications for nanoscale electronic systems.

Contribution

It provides the first detailed measurement of electronic noise at high bias in atomic-scale junctions and evaluates possible mechanisms for enhanced noise beyond ionic heating effects.

Findings

Noise is consistent with shot noise at low bias.

Nonlinear noise increase observed at high bias.

Flicker noise and bulk heating are unlikely causes.

Abstract

Heating in nanoscale systems driven out of equilibrium is of fundamental importance, has ramifications for technological applications, and is a challenge to characterize experimentally. Prior experiments using nanoscale junctions have largely focused on heating of ionic degrees of freedom, while heating of the electrons has been mostly neglected. We report measurements in atomic-scale Au break junctions, in which the bias-driven component of the current noise is used as a probe of the electronic distribution. At low biases ($<$ 150~mV) the noise is consistent with expectations of shot noise at a fixed electronic temperature. At higher biases, a nonlinear dependence of the noise power is observed. We consider candidate mechanisms for this increase, including flicker noise (due to ionic motion), heating of the bulk electrodes, nonequilibrium electron-phonon effects, and local heating of the electronic distribution impinging on the ballistic junction. We find that flicker noise and bulk heating are quantitatively unlikely to explain the observations. We discuss the implications of these observations for other nanoscale systems, and experimental tests to distinguish vibrational and electron interaction mechanisms for the enhanced noise.