# Three in Many: Efimov physics in the presence of a Fermi sea

## TL;DR

This paper investigates how a Fermi sea influences Efimov physics in a Li-Cs atomic mixture, revealing non-monotonic effects and a new universal scaling law for Efimov states in many-body environments.

## Contribution

It introduces a theoretical framework showing how a Fermi sea modifies Efimov states, including a universal scaling law and non-monotonic behavior, relevant for cold atom experiments.

## Key findings

- Fermi sea induces attractive or repulsive interactions depending on $k_F|a_s|$
- Efimov states exhibit non-monotonic behavior with fermion density
- A generalized universal scaling law for dressed Efimov states

## Abstract

Motivated by recent experiments on $^{6}$Li-$^{133}$Cs atomic mixtures with high mass imbalance, we study the Efimov correlation in atomic system of two heavy bosons ($^{133}$Cs) immersed in a bath of light fermions ($^{6}$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 underlying Fermi sea plays distinct roles in the Efimov-type binding of bosons. Namely, in the regime $k_F|a_s|\lesssim 1$ ($k_F|a_s|\gtrsim1$), the Fermi sea induces an attractive (repulsive) effective interaction between bosons and thus favors (disfavors) the formation of bound state, which can be seen as the Efimov trimer dressed by the fermion cloud. Interestingly, this implies a non-monotonic behavior of these bound states as increasing the fermion density (or $k_F$). Moreover, we establish a generalized universal scaling law for the emergence/variation of such dressed Efimov bound states when incorporating a new scale ($k_F$) brought by the Fermi sea. These results can be directly tested in Li-Cs cold atoms experiment by measuring the modified bound state spectrum and the shifted Efimov resonance, which manifest an emergent non-trivial Efimov correlation in a fermionic many-body environment.