Evidence for a Spatially-Modulated Superfluid Phase of $^3$He under Confinement

TL;DR

This study investigates the existence of a spatially-modulated superfluid phase of helium-3 under confinement, using NMR measurements in a microfluidic cavity, and finds evidence inconsistent with the predicted stripe phase but compatible with 2D modulation.

Contribution

The paper provides experimental evidence that challenges the predicted stripe phase in confined superfluid helium-3, supporting the presence of a different form of 2D modulated order.

Findings

Stripe phase is ruled out by NMR measurements.

Results are consistent with 2D modulated superfluid order.

Surface-induced order parameter distortion observed.

Abstract

In superfluid $^3$He-B confined in a slab geometry, domain walls between regions of different order parameter orientation are predicted to be energetically stable. Formation of the spatially-modulated superfluid stripe phase has been proposed. We confined $^3$He in a 1.1 $\mu$m high microfluidic cavity and cooled it into the B phase at low pressure, where the stripe phase is predicted. We measured the surface-induced order parameter distortion with NMR, sensitive to the formation of domains. The results rule out the stripe phase, but are consistent with 2D modulated superfluid order.