Crystalline order in superfluid 3He films

TL;DR

This paper predicts an inhomogeneous, striped superfluid phase in thin films of superfluid 3He, arising from a spontaneous breaking of translational symmetry, with potential experimental signatures in transport and NMR.

Contribution

It introduces a new inhomogeneous phase in superfluid 3He films, characterized by spontaneous translational symmetry breaking and a periodic lattice of degenerate phases.

Findings

Inhomogeneous striped phase exists between critical thicknesses D_{c_2} and D_{c_1}.

Instability at D_{c_2} is a single-mode, leading to stripe order.

Numerical calculations confirm a second-order transition to a periodic lattice of B-like phases.

Abstract

We predict an inhomogeneous phase of superfluid 3He films in which translational symmetry is spontaneously broken in the plane of the film. This phase is energetically favored over a range of film thicknesses, $D_{c_2}(T)<D<D_{c_1}(T)$, separating distinct homogeneous superfluid phases. The instability at the critical film thickness, $D_{c_2}\approx 9 \xi(T)$, is a single-mode instability generating striped phase order in the film. Numerical calculations of the order parameter and free energy indicate a second-order instability to a periodic lattice of degenerate B-like phases separated by domain walls at $D_{c_1}\approx 12 \xi(T)$. The striped phase should be identifiable in transport and nuclear magnetic resonance experiments.