Orbital-Flop Transition of Angular Momentum in a Topological Superfluid

TL;DR

This paper reports the discovery of an abrupt, hysteresis-free transition in the orientation of orbital angular momentum in superfluid helium-3, demonstrating spontaneous reorientation of its order parameter.

Contribution

It reveals an unusual orbital-flop transition in superfluid helium-3, showing spontaneous reorientation of the order parameter without hysteresis or external competition.

Findings

Identified an abrupt orbital-flop transition in superfluid helium-3

Transition occurs without hysteresis or external stimuli

Demonstrates spontaneous reorientation of the superfluid's order parameter

Abstract

The direction of the orbital angular momentum of the $B$-phase of superfluid $^3$He can be controlled by engineering the anisotropy of the silica aerogel framework within which it is imbibed. In this work, we report our discovery of an unusual and abrupt `orbital-flop' transition of the superfluid angular momentum between orientations perpendicular and parallel to the anisotropy axis. The transition has no hysteresis, warming or cooling, as expected for a continuous thermodynamic transition, and is not the result of a competition between strain and magnetic field. This demonstrates the spontaneous reorientation of the order parameter of an unconventional BCS condensate.