Integrable models for asymmetric Fermi superfluids: Emergence of a new exotic pairing phase

TL;DR

This paper presents an exactly-solvable model for asymmetric Fermi superfluids, revealing a new exotic pairing phase that combines inhomogeneity with an interior gap, and maps the quantum phase diagram including strong coupling regimes.

Contribution

The paper introduces a novel exactly-solvable model that captures the competition between LOFF and breached-pair phases, discovering a new stable exotic pairing phase.

Findings

Identifies a new stable exotic pairing phase combining inhomogeneity and interior gap.

Proves the phase is the exact ground state in the strong coupling limit.

Shows the phase can be energetically favorable at finite interaction strengths.

Abstract

We introduce an exactly-solvable model to study the competition between the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) and breached-pair superfluid in strongly interacting ultracold asymmetric Fermi gases. One can thus investigate homogeneous and inhomogeneous states on an equal footing and establish the quantum phase diagram. For certain values of the filling and the interaction strength, the model exhibits a new stable exotic pairing phase which combines an inhomogeneous state with an interior gap to pair-excitations. It is proven that this phase is the exact ground state in the strong coupling limit, while numerical examples demonstrate that also at finite interaction strength it can have lower energy than the breached-pair or LOFF states.