Pairing in ultracold Fermi gases in the lowest landau level

G. Moller 1, Th. Jolicoeur 2, N. Regnault 3

Physical Review A: Atomic, Molecular and Optical Physics 79 (2009) 033609

We study a rapidly rotating gas of unpolarized spin-1/2 ultracold fermions in the two-dimensional regime when all atoms reside in the lowest Landau level. Due to the presence of the spin degree of freedom both s-wave and p-wave interactions are allowed at ultralow temperatures. We investigate the phase diagram of this system as a function of the filling factor of the lowest Landau level and of the ratio between s- and p-wave interaction strengths. We show that the presence of attractive interactions induces a wide regime of phase separation with formation of maximally compact droplets that are either fully polarized or spin-singlet. When there is no phase separation, we give evidence for fractional quantum Hall states. Most notably we find that at the filling nu = 2/3 there is a singlet state accounted for by composite fermion theory which competes with an Abelian state of composite spin-singlet Bose molecules with Laughlin correlations. By fine tuning of the scattering lengths it is possible to create the non-Abelian critical Haldane-Rezayi state for nu = 1/2 and the permanent state of Moore and Read for nu = 1. For purely repulsive interactions, we also find evidence for a gapped Halperin state at nu = 2/5.

  • 1. TCM Group, Cavendish Laboratory,
    Cavendish Laboratory Cambridge
  • 2. Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS),
    CNRS : UMR8626 – Université Paris XI - Paris Sud
  • 3. Laboratoire Pierre Aigrain (LPA),
    CNRS : UMR8551 – Université Paris VI - Pierre et Marie Curie – Université Paris VII - Paris Diderot – Ecole Normale Supérieure de Paris - ENS Paris