Breakdown of Universality for Unequal-Mass Fermi Gases with Infinite Scattering Length

We treat small trapped unequal-mass two-component Fermi gases at unitarity within a nonperturbative 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 and four-body resonances at kappa = 12.314(2) and 10.4(2), respectively, as well as surprisingly large finite-range effects. These findings have profound implications for ongoing experimental efforts and quantum simulation proposals that utilize unequal-mass atomic Fermi gases.