Recent advances in the theory of the BCS–BEC crossover for fermionic superfluidity

Abstract

The BCS–BEC crossover realized experimentally with ultra-cold Fermi gases may be considered as one of the important scientific achievements occurred during the last several years. The flexibility for operating on these systems on the experimental side and the full control of the relevant system degrees of freedom on the theoretical side make quite stringent at a fundamental level the comparison between the experimental data and the corresponding theoretical calculations. Here, we briefly survey recent theoretical advances resting on a diagrammatic approach at equilibrium that improves in a systematic way on the widely used t-matrix approach, yielding a quite good comparison between theory and experiments for several physical quantities of interest. It is proposed that the physical phenomena underlying this theoretical approach may also be relevant to the superconducting phase of condensed-matter materials which cannot be described by the standard BCS theory.