The evolution from BCS to BEC superfluidity in the presence of disorder

Abstract

We describe the effects of disorder on the critical temperature of $s$-wave superfluids from the BCS to the BEC regime, with direct application to ultracold fermions. We use the functional integral method and the replica technique to study Gaussian correlated disorder due to impurities, and we discuss how this system can be generated experimentally. In the absence of disorder, the BCS regime is characterized by pair breaking and phase coherence temperature scales which are essentially the same allowing strong correlations between the amplitude and phase of the order parameter for superfluidity. As non-pair breaking disorder is introduced the largely overlapping Cooper pairs conspire to maintain phase coherence such that the critical temperature remains essentially unchanged, and Anderson's theorem is satisfied. However in the BEC regime the pair breaking and phase coherence temperature scales are very different such that non-pair breaking disorder can affect dramatically phase coherence, and thus the critical temperature, without the requirement of breaking tightly-bound fermion pairs simultaneously. In this case, Anderson's theorem does not apply, and the critical temperature can be more easily reduced in comparison to the BCS limit. Lastly, we find that the superfluid is more robust against disorder in the intermediate region near unitarity between the two regimes.

References in corpus (8)

• Direct observation of Anderson localization of matter-waves in a controlled disorder
• Evidence for Superfluidity of Ultracold Fermions in an Optical Lattice
• Molecules of Fermionic Atoms in an Optical Lattice
• Anderson localization in Bose-Einstein condensates
• Fermi-Fermi Mixtures in the Strong Attraction Limit
• BCS-BEC crossover in a random external potential
• Nonzero orbital angular momentum superfluidity in ultracold Fermi gases
• Superfluid-insulator transition and BCS-BEC crossover in dirty ultracold Fermi gas

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• Transport regimes of cold gases in a two-dimensional anisotropic disorder
• Anderson localization of pairs in bichromatic optical lattices
• Systematic investigation of the effects of disorder at the lowest order throughout the BCS-BEC crossover
• Dipole oscillations of fermionic superfluids along the BEC-BCS crossover in disordered potentials
• Impurity effects on BCS-BEC crossover in ultracold atomic Fermi gases
• Effect of Disorder in BCS-BEC Crossover
• The Gor'kov and Melik-Barkhudarov correction to the mean-field critical field transition to Fulde-Ferrell-Larkin-Ovchinnikov states
• Investigating Dirty Crossover through Fidelity Susceptibility and Density of States
• Effect of Weak Disorder on the BCS-BEC crossover in a two-dimensional Fermi Gas
• Quenched disorder and the BCS-BEC crossover in the Hubbard model
• Self-consistent inclusion of disorder in the BCS-BEC crossover near the critical temperature