Two-band superfluidity and intrinsic Josephson effect in alkaline-earth Fermi gases across an orbital Feshbach resonance

TL;DR

This paper demonstrates that an alkaline-earth Fermi gas near an orbital Feshbach resonance behaves like a two-band superconductor, revealing complex pairing phenomena and phase competition in a cold atom system.

Contribution

It establishes an exact analogy between the many-body Hamiltonian of the Fermi gas and two-band superconductors, and explores phase competition in the BCS-BEC crossover.

Findings

Exact analogy with two-band superconductors

Identification of in-phase and -phase solutions

Analysis of phase competition across the BCS-BEC crossover

Abstract

We first show that the many-body Hamiltonian governing the physical properties of an alkaline-earth Yb-173 Fermi gas across the recently-realized orbital Feshbach resonance is exactly analogous to that of two-band s-wave superconductors with contact interactions: i.e., even though the free-particle bands have a tunable energy offset in between and are coupled by a Josephson-type attractive inter-band pair scattering, the intra-band interactions have exactly the same strength. We then introduce two intra-band order parameters within the BCS mean-field approximation, and investigate the competition between their in-phase and out-of-phase (i.e., the so-called \pi-phase) solutions in the entire BCS-BEC evolution at zero temperature.