On the Stability of the Repulsive Fermi Gas with Contact Interactions

Abstract

We report the creation and the study of the stability of a repulsive quasi-homogeneous spin-1/2 Fermi gas with contact interactions. For the range of scattering lengths a explored, the dominant mechanism of decay is a universal three-body recombination towards a Feshbach bound state. We observe that the recombination coefficient K3 ∝ kina 6 , where the first factor, the average kinetic energy per particle kin, arises from a three-body threshold law, and the second one from the universality of recombination. Both scaling laws are consequences of Pauli blocking effects in three-body collisions involving two identical fermions. As a result of the interplay between Fermi statistics and the momentum dependence of the recombination process, the system exhibits non-trivial temperature dynamics during recombination, alternatively heating or cooling depending on its initial quantum degeneracy. The measurement of K3 provides an upper bound for the interaction strength achievable in equilibrium for a uniform repulsive Fermi gas.