Dimensional crossover of superfluid $^{3}$He in a magnetic field

TL;DR

This paper theoretically explores how the phase diagram of superfluid helium-3 changes from three-dimensional to quasi-two-dimensional behavior under nanoscale confinement and magnetic fields, providing detailed predictions to guide experiments.

Contribution

It presents a comprehensive analysis of the phase crossover in superfluid helium-3 in confined geometries using Ginzburg--Landau theory, including analytical insights and phase diagrams for various parameters.

Findings

Smooth crossover from 3D to quasi-2D phase diagram at nanometer scales

Analytical and numerical phase structure predictions for general free energy coefficients

Phase diagrams computed as functions of pressure, temperature, slab height, and magnetic field

Abstract

Motivated by recent experiments on superfluid $^3$He in nanoscale-confined geometries, we theoretically investigate the associated phase diagram in a slab geometry and perpendicular magnetic field as the size of confinement is varied. Our analysis is based on minimizing the Ginzburg--Landau free energy for the $3\times 3$ matrix superfluid order parameter for three different boundary conditions. We observe a smooth crossover from the phase diagram of the 3D system to the quasi-2D limit for slab heights of several hundred nanometres and magnetic fields of several kilogauss. We illuminate that, despite the apparent complexity of the underlying equations, many precise numerical and even analytical statements can be made about the phase structure for general values of the coefficients of the free energy functional, which can in turn be used to constrain or measure these parameters. To guide future experimental studies, we compute the phase diagram in dependence of pressure, temperature, slab height, and magnetic field.