Dephasing of Cooper pairs and subgap electron transport in superconducting hybrids

TL;DR

This paper investigates how electron-electron interactions limit the penetration of Cooper pairs into normal metals in superconductor-normal metal hybrids, revealing a finite dephasing length that affects subgap conductance measurements.

Contribution

It introduces the concept of a finite Cooper pair dephasing length due to electron-electron interactions, which remains finite at low temperatures and influences subgap conductance.

Findings

Dephasing length $L_\varphi$ remains finite at $T \to 0$

Electron-electron interactions restrict Cooper pair penetration

Subgap conductance can be used to measure $L_\varphi$

Abstract

We argue that electron-electron interactions fundamentally restrict the penetration length of Cooper pairs into a diffusive normal metal (N) from a superconductor (S). At low temperatures this Cooper pair dephasing length $L_\varphi$ remains finite and does not diverge at $T \to 0$. We evaluate the subgap conductance of NS hybrids in the presence of electron-electron interactions and demonstrate that this new length $L_\varphi$ can be directly extracted from conductance measurements in such structures.