Effect of correlated disorder on the temperature of unconventional Cooper pairing (3He in aerogel)

TL;DR

This paper investigates how impurity correlations in aerogel influence the transition temperature of unconventional superfluid 3He, providing a theoretical model that aligns well with experimental observations.

Contribution

It introduces a model accounting for impurity correlations and fractal aerogel structure to explain the suppression of $T_c$ in superfluid 3He.

Findings

Impurity correlations significantly suppress $T_c$ when correlation length exceeds coherence length.

A simple expression relates $T_c$ decrease to aerogel structure factor.

The model agrees satisfactorily with experimental data.

Abstract

Using liquid 3He in aerogel as an example, it is shown that correlations in positions of impurities affect the temperature $T_c$ of transition of Fermi liquid in an unconventional superfluid or superconductive state. The effect is significant if the correlation length for impurities is greater than the coherence length in the superfluid or superconductive state $\xi_0$. For 3He in aerogel the suppression of $T_c$ is expressed in terms of the structure factor of aerogel. With the account of the fractal structure of aerogel a simple expression is obtained for the decrease of $T_c$ from its clean value. This expression is in a satisfactory agreement with experimental data.