Current fluctuations near to the 2D superconductor-insulator quantum critical point

TL;DR

This paper investigates current fluctuations near a 2D superconductor-insulator quantum critical point, revealing a universal scaling of noise with electric field and temperature, and explaining suppression of shot noise due to strong correlations.

Contribution

It demonstrates a universal scaling form of current noise near the quantum critical point using a Boltzmann-Langevin approach and explores the physical interpretation of noise suppression.

Findings

Current noise scales as $S_j=T \, \Phi[T/T_{eff}(E)]$ with $T_{eff} \propto \sqrt{E}$.

At strong electric fields, noise follows $S_j \propto \sqrt{E}$.

Strong correlations suppress shot noise, leading to diverging carrier charge or out-of-equilibrium Johnson noise.

Abstract

Systems near to quantum critical points show universal scaling in their response functions. We consider whether this scaling is reflected in their fluctuations; namely in current-noise. Naive scaling predicts low-temperature Johnson noise crossing over to noise power $\propto E^{z/(z+1)}$ at strong electric fields. We study this crossover in the metallic state at the 2d z=1 superconductor/insulator quantum critical point. Using a Boltzmann-Langevin approach within a 1/N-expansion, we show that the current noise obeys a scaling form $S_j=T \Phi[T/T_{eff}(E)]$ with $T_{eff} \propto \sqrt{E}$. We recover Johnson noise in thermal equilibrium and $S_j \propto \sqrt{E}$ at strong electric fields. The suppression from free carrier shot noise is due to strong correlations at the critical point. We discuss its interpretation in terms of a diverging carrier charge $\propto 1/\sqrt{E}$ or as out-of-equilibrium Johnson noise with effective temperature $\propto \sqrt{E}$.