Strong Fulde-Ferrell Larkin-Ovchinnikov pairing fluctuations in polarized Fermi systems

Michele Pini,Giancarlo Calvanese Strinati,Pierbiagio Pieri

doi:10.1103/physrevresearch.3.043068

Abstract

We calculate the pair susceptibility of an attractive spin-polarized Fermi gas in the normal phase, as a function of the pair momentum. Close to unitarity, we find a strong enhancement of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing fluctuations over an extended region of the temperature-polarization phase diagram, which manifests itself as a pronounced peak in the pair-momentum distribution at a finite pair momentum. This peak should be amenable to experimental observation at achievable temperatures in a box-like trapping potential, as a fingerprint of FFLO pairing. Our calculations rest on a self-consistent t-matrix approach which, for the unitary balanced Fermi gas, has been validated against experimental data for several thermodynamic quantities.

Highlights

One of the main motivations that some time ago [1,2] initiated a vibrant experimental and theoretical research activity on ultracold polarized attractive Fermi gases [3], was the search for exotic superfluid phases, like the FFLO phase predicted many years before by Fulde and Ferrell [4] and Larkin and Ovchinnikov [5] for superconductors in a strong magnetic field
We find a strong enhancement of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing fluctuations over an extended region of the temperature-polarization phase diagram, which manifests itself as a pronounced peak in the pair-momentum distribution at a finite pair momentum
Close to unitarity [15], we find that the pair susceptibility is considerably enhanced at a finite value Q0(r) proportional to χpair (Q0) of Q(= |Q|) over an extended region of the temperature-polarization phase diagram, such that it should be possible to observe this strong tendency towards FFLO ordering at experimentally achievable temperatures in the normal phase

Summary

Introduction

One of the main motivations that some time ago [1,2] initiated a vibrant experimental and theoretical research activity on ultracold polarized attractive Fermi gases [3], was the search for exotic superfluid phases, like the FFLO phase predicted many years before by Fulde and Ferrell [4] and Larkin and Ovchinnikov [5] for superconductors in a strong magnetic field. This phase is characterized by pairing at finite center-of-mass momentum of the pairs, with spatially dependent gap parameter (r) = Q0 eiQ0·r for the Fulde-Ferrell (FF) and (r) = Q0 cos(Q0 · r) for the Larkin-Ovchinnikov (LO) solutions.

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Conclusion