Impact of Strong Anisotropy on Phase Diagram of Superfluid $^3$He in Aerogels

TL;DR

This paper investigates how strong anisotropy in aerogels affects the phase diagram of superfluid $^3$He, examining the validity of an Anderson's theorem analog and comparing theoretical predictions with experimental data.

Contribution

It analyzes the impact of strong uniaxial anisotropy on the superfluid phase diagram of $^3$He in aerogels, focusing on the polar phase and the applicability of Anderson's theorem.

Findings

The Anderson's theorem holds under moderate anisotropy for the polar phase.

The transition temperature $T_c$ and energy gap behavior are affected by anisotropy.

Breakdown of the theorem occurs under certain strong anisotropic conditions.

Abstract

Recently, one analog of the Anderson's Theorem for the $s$-wave superconductor has attracted much interest in the context of the $p$-wave polar pairing state of superfluid $^3$He in a model aerogel in the limit of strong uniaxial anisotropy. We discuss to what extent the theorem is satisfied in the polar phase in real aerogels by examining the normal to polar transition temperature $T_c$ and the low temperature behavior of the superfluid energy gap under an anisotropy of a moderate strength and comparing the obtained results with experimental data. The situation in which the Anderson's theorem clearly breaks down is also discussed.