The impact of speckle disorder on a superfluid Fermi system

Optical lattice experiments which probe the effect of disorder on superfluidity often use a speckle pattern for generating the disorder. Such speckle disorder is spatially correlated. While fermionic superfluidity in the presence of uncorrelated disorder is well studied, the impact of correlated disorder, particularly on thermal properties of the superfluid, is poorly understood. We provide a detailed study of the impact of speckle disorder, for varying speckle size and disorder magnitude, on the ground state and thermal properties of a Fermi superfluid. We work in the strong coupling regime of BCS-BEC crossover in a two dimensional lattice. For a fixed disorder strength, an increase in speckle size leads to smoothening of the self-consistent background potential, increase in the critical disorder needed for a superfluid-insulator transition, and an increase in superfluid $T_c$ . Along with these hints at decrease in effective disorder, speckle correlations also suppress the superfluid gap and the gap formation temperature - effects normally associated with increasing disorder. We correlate these effects with the effective potential and the single particle localisation effects in the ground state
Comment: 12 pages, 15 figures. going to appear in Phys Rev B