Modification of the 3He Phase Diagram by Anisotropic Disorder

TL;DR

This study investigates how anisotropic disorder introduced by uniaxial compression of aerogel alters the phase diagram of superfluid 3He, notably stabilizing the A phase over a broader region and modifying critical points.

Contribution

It provides experimental evidence that anisotropic disorder in aerogel modifies the 3He phase diagram, including the disappearance of the polycritical point and stabilization of the A phase.

Findings

A broad A phase region is stabilized in compressed aerogel.

The polycritical point of pure 3He is absent in the modified phase diagram.

The A phase reappears on warming from the B phase before superfluidity ends.

Abstract

Motivated by the recent prediction that uniaxially compressed aerogel can stabilize the anisotropic A phase over the isotropic B phase, we measure the pressure dependent superfluid fraction of 3He entrained in 10% axially compressed, 98% porous aerogel. We observe that a broad region of the temperature-pressure phase diagram is occupied by the metastable A phase. The reappearance of the A phase on warming from the B phase, before superfluidity is extinguished at Tc, is in contrast to its absence in uncompressed aerogel. The phase diagram is modified from that of pure 3He, with the disappearance of the polycritical point (PCP) and the appearance of a region of A phase extending below the PCP of bulk 3He, even in zero applied magnetic field. The expected alignment of the A phase texture by compression is not observed.