Breakdown of universality for unequal-mass Fermi gases with infinite scattering length

Abstract

We treat small trapped unequal-mass two-component Fermi gases at unitarity within a non-perturbative microscopic framework and investigate the system properties as functions of the mass ratio $\kappa$, and the numbers $N_{1}$ and $N_2$ of heavy and light fermions. While equal-mass Fermi gases with infinitely large interspecies s-wave scattering length $a_s$ are universal, we find that unequal mass Fermi gases are, for sufficiently large $\kappa$ and in the regime where Efimov physics is absent, not universal. In particular, the $(N_1,N_2)=(2,1)$ and $(3,1)$ systems exhibit three-body (3b) and four-body (4b) resonances at $\kappa = 12.314(2)$ and $10.4(2)$, respectively, as well as surprisingly large finite-range (FR) effects. These findings have profound implications for ongoing experimental efforts and quantum simulation proposals that utilize unequal-mass atomic Fermi gases.