Efimov physics in the presence of a Fermi sea

Abstract

Motivated by recent experiments on $^{6}\mathrm{Li}\text{\ensuremath{-}}^{133}\mathrm{Cs}$ atomic mixtures with high mass imbalance, we study the Efimov correlation in an atomic system of two heavy bosons ($^{133}\mathrm{Cs}$) immersed in a bath of light fermions ($^{6}\mathrm{Li}$). Using the Born-Oppenheimer approximation, we identify two different regimes, depending on the Fermi momentum of light fermions (${k}_{F}$) and the boson-fermion scattering length ${a}_{s}(<0)$, where the presence of an underlying Fermi sea plays distinct roles in the Efimov-type binding of bosons. Namely, in the regime ${k}_{F}|{a}_{s}|\ensuremath{\lesssim}1$ (${k}_{F}|{a}_{s}|\ensuremath{\gtrsim}1$), the Fermi sea induces an attractive (repulsive) effective interaction between bosons and thus favors (disfavors) the formation of a bound state, which can be seen as an Efimov trimer dressed by a fermion cloud. Interestingly, this implies nonmonotonic behavior of these bound states as increasing the fermion density (or ${k}_{F}$). Moreover, we establish a generalized universal scaling law for the emergence and variation of such dressed Efimov bound states when incorporating a new scale (${k}_{F}$) brought on by the Fermi sea. These results can be directly tested in Li-Cs cold-atom experiments by measuring the modified bound-state spectrum and the shifted Efimov resonance, which manifest an emergent nontrivial Efimov correlation in a fermionic many-body environment.