Current noise enhancement: channel mixing and possible nonequilibrium phonon backaction in atomic-scale Au junctions

TL;DR

This study investigates bias-dependent shot noise in atomic-scale gold junctions at 77 K, revealing significant noise enhancement likely due to channel mixing or nonequilibrium phonon effects, extending understanding beyond room temperature behavior.

Contribution

It provides new experimental data on shot noise at low temperature and explores potential mechanisms for noise enhancement in atomic junctions, highlighting the need for further theoretical development.

Findings

Enhanced Fano factor up to ten times at 77 K

Bias dependence suggests channel mixing or phonon backaction

Results differ from previous room temperature measurements

Abstract

We report measurements of the bias dependence of the Fano factor in ensembles of atomic-scale Au junctions at 77 K. Previous measurements of shot noise at room temperature and low biases have found good agreement of the Fano factor with the expectations of the Landauer- B\"uttiker formalism, while enhanced Fano factors have been observed at biases of hundreds of mV [R. Chen et al., Sci. Rep. 4, 4221 (2014)]. We find even stronger enhancement of shot noise at 77 K with an "excess" Fano factor up to ten times the low bias value. We discuss the observed ensemble Fano factor bias dependence in terms of candidate models. The results are most consistent with either a bias-dependent channel mixing picture or a model incorporating noise enhancement due to current-driven, nonequilibrium phonon populations, though a complete theoretical treatment of the latter in the ensemble average limit is needed.