Quantum liquid crystals in imbalanced Fermi gas: fluctuations and fractional vortices in Larkin-Ovchinnikov states

TL;DR

This paper develops a nonlinear low-energy model of the Larkin-Ovchinnikov state in imbalanced Fermi gases, revealing its liquid crystal nature, enhanced fluctuations, and unique topological defects leading to novel phase transitions.

Contribution

It introduces a fully nonlinear description of the LO state as a smectic liquid crystal with strong fluctuations and explores its topological defects and phase transitions in 2D and 3D.

Findings

LO state exhibits algebraic order at nonzero temperature in 3D

Presence of half-integer vortex-dislocation defects and their unbinding transitions

LO state is unstable to a charge-4 nematic superfluid in 2D

Abstract

We develop a low-energy model of a unidirectional Larkin-Ovchinnikov (LO) state. Because the underlying rotational and translational symmetries are broken spontaneously, this gapless superfluid is a smectic liquid crystal, that exhibits fluctuations that are qualitatively stronger than in a conventional superfluid, thus requiring a fully nonlinear description of its Goldstone modes. Consequently, at nonzero temperature the LO superfluid is an algebraic phase even in 3d. It exhibits half-integer vortex-dislocation defects, whose unbinding leads to transitions to a superfluid nematic and other phases. In 2d at nonzero temperature, the LO state is always unstable to a charge-4 nematic superfluid. We expect this superfluid liquid-crystal phenomenology to be realizable in imbalanced resonant Fermi gases trapped isotropically.