Non-universal Fermi polaron in quasi two-dimensional quantum gases

TL;DR

This paper investigates the behavior of an impurity in a quasi-two-dimensional Fermi gas, revealing a non-universal transition from polaron to molecule states depending on interaction strength and particle density.

Contribution

It introduces a variational and two-channel model approach to analyze polaron-molecule transition and its non-universal nature in quasi-2D Fermi gases.

Findings

Ground state transitions from polaron to molecule with increasing interaction

Critical interaction strength depends on particle density

Excited repulsive polaron exhibits similar non-universal behavior

Abstract

We consider an impurity problem in a quasi-two-dimensional Fermi gas, where a spin-down impurity is immersed in a Fermi sea of N spin-up atoms. Using a variational approach and an effective two-channel model, we obtain the energies of the system for a wide range of interaction strength and for various different mass ratios between the impurity and the back ground fermion in the context of heteronuclear mixture. It is demonstrated that in a quasi-two-dimensional Fermi gas there exists a transition of the ground state from polaron in the weakly interacting region to molecule in the strongly interacting region. The critical interaction strength of the polaron-molecule transition is non-universal and depends on the particle density of the background Fermi sea. We also investigate the properties of the excited repulsive polaron state, and find similar non-universal behavior.