Effect of Magnetic Scattering on Superfluid Transition of 3He in Nematic Aerogel

TL;DR

This study investigates how magnetic scattering affects the superfluid transition of helium-3 in nematic aerogel under high magnetic fields, revealing nonlinear increases in transition temperature and discrepancies with existing theories.

Contribution

It provides experimental data on superfluid transition behavior of helium-3 in nematic aerogel under magnetic fields, highlighting the impact of magnetic scattering channels and theoretical mismatches.

Findings

Superfluid transition temperature increases nonlinearly with magnetic field.

Magnetic scattering suppresses the expected increase compared to bulk A1 phase.

Quantitative mismatch with existing theoretical models.

Abstract

We present results of high magnetic field experiments in pure $^3$He (in the absence of $^4$He coverage) in nematic aerogel. In this case the aerogel strands are covered with few atomic layers of solid paramagnetic $^3$He, which enables the spin-exchange mechanism for $^3$He quasiparticles scattering. Our earlier NMR experiments showed that in low fields, instead of the polar phase, the A phase is expected to emerge in nematic aerogel. We use a vibrating wire resonator with the sample of aerogel attached to it and measure temperature dependencies of resonance properties of the resonator at different magnetic fields. A superfluid transition temperature of $^3$He in aerogel, obtained from the experiments, increases nonlinearly in applied magnetic field. And this increase is suppressed compared with that for bulk A$_1$ phase, which we attribute to an influence of the magnetic scattering channel, previously considered theoretically for the case of $^3$He confined in isotropic silica aerogel. However, we observe the essential quantitative mismatch with theoretical expectations.