Gapless excitations in strongly fluctuating superconducting wires

TL;DR

This paper investigates the low-temperature properties of thin superconducting wires undergoing quantum phase-slip proliferation, revealing a gapless, weakly insulating phase with linear temperature dependence of conductivity caused by electron-electron interactions.

Contribution

It demonstrates that the phase with destroyed superconductivity exhibits gapless excitations and linear conductivity decline, challenging the traditional insulator perspective.

Findings

Conductivity decreases linearly with temperature in the phase.

The phase exhibits a gapless excitation spectrum.

Electron-electron interactions induce pair breaking.

Abstract

We study the low temperature tunneling density of states of thin wires where superconductivity is destroyed through quantum phase-slip proliferation. Although this regime is believed to behave as an insulator, we show that for a large temperature range this phase is characterized by a conductivity falling off at most linearly with temperature, and has a gapless excitation spectrum. This novel conducting phase results from electron-electron interaction induced pair breaking. Also, it may help clarify the low temperature metallic features found in films and wires whose bulk realization is superconducting.