Hetero pairing and component-dependent pseudogap phenomena in an ultracold Fermi gas with mass imbalance

Abstract

We investigate the superfluid phase transition and single-particle excitations in the BCS (Bareen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an ultracold Fermi gas with mass imbalance. In our recent paper [R. Hanai, et. al., Phys. Rev. A 88, 053621 (2013)], we showed that an extended $T$-matrix approximation (ETMA) can overcome the serious problem known in the ordinary (non-self-consistent) $T$-matrix approximation that it unphysically gives double-valued superfluid phase transition temperature $T_{\mathrm{c}}$ in the presence of mass imbalance. However, at the same time, the ETMA was also found to give the vanishing $T_{\mathrm{c}}$ in the weak-coupling and highly mass-imbalanced case. In this paper, we inspect the correctness of this ETMA result, using the self-consistent $T$-matrix approximation (SCTMA). We show that the vanishing $T_{\mathrm{c}}$ is an artifact of the ETMA, coming from an internal inconsistency of this theory. The superfluid phase transition actually always occurs, irrespective of the ratio of mass imbalance. We also apply the SCTMA to the pseudogap problem in a mass-imbalanced Fermi gas. We show that pairing fluctuations induce different pseudogap phenomena between the the light component and heavy component. We also point out that a ${}^6$Li-${}^{40}$K mixture is a useful system for the realization of a hetero pairing state, as well as for the study of component-dependent pseudogap phenomena.

arXiv comment27 pages, 14 figures

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• Dynamical instability of a driven-dissipative electron-hole condensate in the BCS-BEC-crossover region
• Strong-coupling corrections to spin susceptibility in the BCS-BEC crossover regime of a superfluid Fermi gas
• Beyond-mean-field description of a trapped unitary Fermi gas with mass and population imbalance
• Precursor of Superfluidity in a Strongly Interacting Fermi Gas with Negative Effective Range
• Shear viscosity and Strong-Coupling Corrections in the BCS-BEC crossover Regime of an Ultracold Fermi Gas
• Thermal transitions, pseudogap behavior and BCS-BEC crossover in Fermi-Fermi mixtures
• Spectral functions of the strongly interacting 3D Fermi gas
• Pauli limited d-wave superconductors: Quantum breached pair phase and thermal transitions
• Mass-Imbalanced Superconductivity in Effective Two-Channel Kondo Lattice
• Isothermal compressibility and effects of multi-body molecular interactions in a strongly interacting ultracold Fermi gas
• Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with broken spin rotation symmetry
• Kovtun-Son-Starinets Conjecture and Effects of Mass Imbalance in the Normal State of an Ultracold Fermi Gas in the BCS-BEC Crossover Region
• Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with broken spin rotation symmetry. II. Three dimensional continuum case
• Interplay of the pseudogap and the BCS gap for heteropairs in ${}^{40}$K-${}^6$Li mixture