Fermion Pairing across a Dipolar Interaction Induced Resonance

TL;DR

This paper investigates the many-body physics of a two-component Fermi gas near a dipolar interaction induced resonance, revealing isotropic pairing at low density and complex phase transitions involving singlet and triplet pairings at high density.

Contribution

It demonstrates that despite anisotropic dipolar interactions, the low-density pairing resembles isotropic s-wave pairing, and uncovers novel phase transitions with spontaneous time-reversal symmetry breaking.

Findings

Pairing energy comparable to unitary Fermi gas near Feshbach resonance

Transition from singlet to mixed and triplet pairing phases with increasing density

Spontaneous breaking of time-reversal symmetry in mixed pairing state

Abstract

It is known from the solution of the two-body problem that an anisotropic dipolar interaction can give rise to s-wave scattering resonances, which are named as dipolar interaction induced resonaces (DIIR). In this letter, we study zero-temperature many-body physics of a two-component Fermi gas across a DIIR. In the low-density regime, it is very striking that the resulting pairing order parameter is a nearly isotropic singlet pairing and the physics can be well described by an s-wave resonant interaction potential with finite range corrections, despite of the anisotropic nature of dipolar interaction. The pairing energy is as strong as a unitary Fermi gas nearby a magnetic Feshbach resonance. In the high density regime, the anisotropic effect plays an important role. We find phase transitions from singlet pairing to a state with mixed singlet and triplet pairing, and then from mixed pairing to pure triplet pairing. The state with mixed pairing spontaneously breaks the time-reversal symmetry.