Pierbiagio Pieri (U. Bologna)
FFLO correlations in polarized ultracold Fermi gases

M. Pini1,2, P. Pieri 3,4, G. Calvanese Strinati1,5
1 CNR-INO, Istituto Nazionale di Ottica, Sede di Sesto Fiorentino, 50019 (FI), Italy. 2 Max-Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany. 
3 Dipartimento di Fisica e Astronomia, Universita di Bologna, I-40127 Bologna (BO), Italy 
4 INFN, Sezione di Bologna, I-40127 Bologna (BO), Italy. 5 School of Science and Technology, Physics Division, Universita di Camerino, 62032 Camerino (MC), Italy.

Quite generally, an imbalance between the densities of spin-up and spin-down fermions hinders pairing and superfluidity in two-component attractive Fermi gases. The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, in which pairs condense at a finite value of center-of-mass momentum to compensate for the mismatch of the two Fermi surfaces, was proposed many years ago as a possible superfluid phase compatible with a finite polarization. In this talk, I will discuss how significant precursor FFLO fluctuation effects appear already in the normal phase of polarized Fermi gases, and how they could be observed experimentally. At zero temperature, I will also discuss how the quasi-particle parameters of the normal Fermi gas are changed when approaching an FFLO quantum critical point. Within a fully selfconsistent t-matrix approach we find that the quasi-particle residues vanish, and the effective masses diverge at the FFLO quantum critical point, with a complete breakdown of the quasi-particle picture that is similar to what is found in heavyfermion materials at an antiferromagnetic quantum critical point.