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

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 173 Yb 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 6 Li and 40 K 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.

Controlling the interaction of ultracold alkaline-earth atoms

“…This forces us to take into account the scattering state in the closed channel, that is to say, the so-called closed channel is not really "closed". The multi-orbital nature brings the physics into a new parameter regime that has not been explored before [39,[58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73]. Here we simply give couple examples.…”

“…First of all, the strong influence of the closed channel leads to a strong momentum dependence of the scattering amplitude, which can lead to an even higher transition temperature for forming Fermi superfluid, comparing to the single-channel wide resonance in alkaline-metal atom [58]. In the superfluid phase, since both two channels are occupied by the scattering states, it requires two order pairing order parameters to describes such a Fermi superfluid, which adds a new twist to the BEC-BCS crossover physics [39,[58][59][60][61][62][63][64][65]. This is reminiscent of multi-band superconductor in solid-state materials.…”

Hidden Pseudogap and Excitation Spectra in a Strongly Coupled Two-Band Superfluid/Superconductor

“…Thanks to these experimental progress, the two-band BCS-BEC crossover theory has been of particular interest in condensed matter and ultracold atomic physics [12][13][14][15][16][17][18][19][20][21][22]. In particular, the FeSe superconductors involve a multiband configuration which plays a crucial role for the BCS-BEC crossover.…”

Resonant pair-exchange scattering and BCS-BEC crossover in a system composed of dispersive and heavy incipient bands: a Feshbach analogy

“…The quantity a can be controlled by an external magnetic field with the magnetic Feshbach resonance associated with the electron-spin degree of freedom with S = 1/2 [38]. Now, a realization of the two-band BCS-BEC crossover has recently been anticipated in Ytterbium Fermi gases [39][40][41][42][43]. In the case of 173 Yb atom with S = 0, the system accommodates the orbital Feshbach resonance, which involves intrachannel and interchannel interactions in a two-channel system having different electron-orbital states, 1 S 0 and 3 P 0 , and nuclearspin states [4,39,44,45].…”