Functional renormalization for the BCS-BEC crossover

Understand

We review the functional renormalization group (RG) approach to the BCS-BEC crossover for an ultracold gas of fermionic atoms.

• Formulated in terms of a scale-dependent effective action, the functional RG interpolates continuously between the atomic or molecular microphysics and the macroscopic physics on large length scales.
• We concentrate on the discussion of the phase diagram as a function of the scattering length and the temperature which is a paradigm example for the non-perturbative power of the functional RG.
• A systematic derivative expansion provides for both a description of the many-body physics and its expected universal features as well as an accurate account of the few-body physics and the associated BEC and BCS limits.