The A-B transition in superfluid 3He under confinement in a thin slab geometry

TL;DR

This study investigates how confinement in a thin slab affects the A-B phase transition in superfluid 3He, revealing a possible stripe phase and a new B-phase nucleation mechanism under high pressure.

Contribution

It provides the first detailed phase diagram of superfluid 3He confined in a nanofluidic cavity, highlighting the role of confinement and strong coupling effects on the A-B transition.

Findings

Small supercooling of the A-phase under confinement

Non-monotonic pressure dependence of supercooling

Evidence for a stripe phase influencing B-phase nucleation

Abstract

The influence of confinement on the topological phases of superfluid 3He is studied using the torsional pendulum method. We focus on the phase transition between the chiral A-phase and the time-reversal-invariant B-phase, motivated by the prediction of a spatiallymodulated (stripe) phase at the A-B phase boundary. We confine superfluid 3He to a single 1.08 {\mu}m thick nanofluidic cavity incorporated into a high-precision torsion pendulum, and map the phase diagram between 0.1 and 5.6 bar. We observe only small supercooling of the A-phase, in comparison to bulk or when confined in aerogel. This has a non-monotonic pressure dependence, suggesting that a new intrinsic B-phase nucleation mechanism operates under confinement, mediated by the putative stripe phase. Both the phase diagram and the relative superfluid fraction of the A and B phases, show that strong coupling is present at all pressures, with implications for the stability of the stripe phase.