Trimers, molecules and polarons in imbalanced atomic Fermi gases

TL;DR

This paper investigates the ground states of impurity atoms in imbalanced Fermi gases, analyzing transitions between polarons, molecules, and trimers, and highlights the enhanced stability of p-wave trimers influenced by the Fermi sea.

Contribution

It introduces a detailed variational approach to study impurity bound states and reveals the stability of p-wave trimers in imbalanced Fermi gases, extending understanding beyond equal-mass systems.

Findings

Fermi sea enhances p-wave trimer stability

Transitions occur outside phase separation regions for large mass ratios

Observable transitions in experiments for imbalanced gases

Abstract

We consider the ground state of a single "spin-down" impurity atom interacting attractively with a "spin-up" atomic Fermi gas. By constructing variational wave functions for polarons, molecules and trimers, we perform a detailed study of the transitions between each of these dressed bound states as a function of mass ratio $r=m_\uparrow/m_\downarrow$ and interaction strength. We find that the presence of a Fermi sea enhances the stability of the $p$-wave trimer, which can be viewed as a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) molecule that has bound an additional majority atom. For sufficiently large $r$, we find that the transitions lie outside the region of phase separation in imbalanced Fermi gases and should thus be observable in experiment, unlike the well-studied equal-mass case.