Influence of Exchange Scattering on Superfluid He-3 states in Nematic Aerogel

TL;DR

This paper investigates how exchange scattering and surface coverage in nematic aerogel influence the superfluid phases of liquid helium-3, revealing that these effects can suppress the polar phase and alter anisotropic scattering properties.

Contribution

It introduces a theoretical analysis of exchange scattering effects on superfluid helium-3 in nematic aerogel, linking surface conditions to phase stability and anisotropy.

Findings

Exchange scattering reduces polar phase stability.

Surface coverage alters scattering anisotropy.

Spin diffusion anisotropy correlates with phase emergence.

Abstract

The superfluid state in bulk liquid $^3$He is realized in the form of A or B phases. Uniaxially anisotropic aerogel (nafen) stabilizes transition from the normal to the polar superfluid state which on further cooling transitions to the axipolar orbital glass state (Phys. Rev. Lett. {\bf 115}, 165304 (2015)). This is the case in nafen aerogel preplated by several atomic layers of $^4$He. When pure liquid $^3$He fills the same nafen aerogel a solid-like layer of $^3$He atoms coats the aerogel structure. The polar state is not formed anymore and a phase transition occurs directly to the axipolar phase (Phys. Rev. Lett. {\bf 120}, 075301 (2018). The substitution of $^4$He by $^3$He atoms at the aerogel surface changes the potential and adds the exchange scattering of quasiparticles on the aerogel strands. A calculation shows that both of these effects can decrease the degree of anisotropy of scattering and suppress the polar phase formation. The derived anisotropy of the spin diffusion coefficient in globally anisotropic aerogel is determined by the same parameter which controls the polar state emergence which allows one to check the effect of anisotropy change for different types of covering.