RKKY (Ruderman–Kittel–Kasuya–Yosida) mechanism and Efimov physics describe two seemingly disconnected quantum phenomena in condensed matter and nuclear physics, respectively. RKKY mechanism mediates long-range interactions of impurities embedded in a degenerate Fermi gas, while Efimov physics describes a universal bound state of three particles with resonant, pairwise interactions. Recent research suggests an intriguing connection between the two scenarios in the strong interaction regime.
We perform experiments on a quantum mixture of heavy bosons (Cs) embedded in light fermions (Li) near an interspecies Feshbach resonance. Interactions between Cs atoms mediated by the Li atoms observed in the weak coupling regime show consistency with the RKKY mechanism, while Efimov trimers manifest in the strong coupling regime. How are the 2 physics mingled? We present new measurements on the Bose-Fermi mixture over the entire weak- to strong-coupling regime, which revealed even more surprises, including the collapsing and revival of phonon modes.