Single-particle Excitations and Strong Coupling Effects in the BCS-BEC Crossover Regime of a Rare-Earth Fermi Gas with an Orbital Feshbach Resonance

TL;DR

This paper theoretically explores the normal-state properties of an ultracold Fermi gas with an orbital Feshbach resonance, revealing strong-coupling effects such as pseudogap formation and unique spectral features in the BCS-BEC crossover.

Contribution

It provides the first detailed analysis of strong-coupling corrections and single-particle excitations in an orbital Feshbach resonance system, highlighting phenomena distinct from magnetic Feshbach resonances.

Findings

Observation of pseudogap in the open channel during BCS-BEC crossover

Identification of particle-hole coexistence in the closed channel due to strong pairing

Characterization of strong-coupling phenomena unique to orbital Feshbach resonances

Abstract

We theoretically investigate normal-state properties of an ultracold Fermi gas with an orbital Feshbach resonance (OFR). Recently, OFR has attracted much attention as a promising pairing mechanism to realize a superfluid 173Yb Fermi gas. Including pairing fluctuations within a T-matrix approximation, and removing effects of an experimentally inaccessible deep bound state, we evaluate strong-coupling corrections to single-particle excitations. With increasing the strength of an OFR-induced tunable pairing interaction, the open channel is shown to exhibit the pseudogap phenomenon in the BCS-BEC crossover region, as in the case of a broad magnetic Feshbach resonance (MFR) in 6Li and 40K Fermi gases. We also show that the strong pairing interaction affects the closed channel, leading to the coexistence of particle and hole branches in the single-particle spectral weight. Since the latter phenomenon cannot be observed in the conventional MFR case, it may be viewed as a characteristic strong-coupling phenomenon peculiar to the OFR case.