Crossover polarons in a strongly interacting Fermi superfluid

Abstract

We investigate the zero-temperature quasiparticle properties of a mobile impurity immersed in a strongly interacting Fermi superfluid at the crossover from a Bose-Einstein condensate (BEC) to a Bardeen--Cooper--Schrieffer (BCS) superfluid, by using a many-body $T$-matrix approach that excludes Efimov trimer bound states. Termed BEC-BCS crossover polaron, or crossover polaron in short, this quasiparticle couples to elementary excitations of a many-body background and therefore could provide a useful probe of the underlying strongly interacting Fermi superfluid. Due to the existence of a significant pairing gap $\Delta$, we find that the repulsive polaron branch becomes less well-defined. In contrast, the attractive polaron branch is protected by the pairing gap and becomes more robust at finite momentum. It remains as a delta-function peak in the impurity spectral function below a threshold $2\Delta$. Above the threshold, the attractive polaron enters the particle-hole continuum and starts to get damped. We predict the polaron energy, residue and effective mass for realistic Bose-Fermi mixtures, where the minority bosonic atoms play the role of impurity. These results are practically useful for future cold-atom experiments on crossover polarons.

10 pages, 6 figures

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• Intersections of ultracold atomic polarons and nuclear clusters: How is a chart of nuclides modified in dilute neutron matter?
• Mobile impurities interacting with a few one-dimensional lattice bosons
• Multidimensional Spectroscopy of Time-Dependent Impurities in Ultracold Fermions
• Two-dimensional polaron spectroscopy of Fermi superfluids
• Polaronic Proton and Diproton Clustering in Neutron-Rich Matter
• Raman spectroscopy of Fermi polarons
• Lattice Bose polarons at strong coupling and quantum criticality
• Fermi spin polaron and dissipative Fermi-polaron Rabi dynamics
• Weakly-interacting Bose-Bose mixtures from the functional renormalisation group
• Super Fermi polaron and Nagaoka ferromagnetism in a two-dimesnional square lattice
• Spectral function of Fermi polarons at finite temperature from a self-consistent many-body $T$-matrix approach in real frequency