Boson-fermion pairing and condensation in two-dimensional Bose-Fermi mixtures

TL;DR

This paper investigates how increasing Bose-Fermi attraction in a two-dimensional mixture affects condensate depletion, pairing, and the emergence of Fermi liquid-like quasi-particles, revealing universal behaviors in key physical quantities.

Contribution

It introduces a diagrammatic T-matrix approach to analyze Bose-Fermi mixtures, highlighting the formation of pairs and quasi-particles with novel properties at zero temperature.

Findings

Condensate is progressively depleted with stronger attraction.

Bose-Fermi pairs form, but some condensate persists.

Universal behavior observed in condensate fraction and Tan's contact.

Abstract

We consider a mixture of bosons and spin-polarized fermions in two dimensions at zero temperature with a tunable Bose-Fermi attraction. By adopting a diagrammatic T-matrix approach, we analyze the behavior of several thermodynamic quantities for the two species as a function of the density ratio and coupling strength, including the chemical potentials, the momentum distribution functions, the boson condensate density, and the Tan's contact parameter. By increasing the Bose-Fermi attraction, we find that the condensate is progressively depleted and Bose-Fermi pairs form, with a small fraction of condensed bosons surviving even for strong Bose-Fermi attraction. This small condensate proves sufficient to hybridize molecular and atomic states, producing quasi-particles with unusual Fermi liquid features. A nearly universal behavior of the condensate fraction, the bosonic momentum distribution, and Tan's contact parameter with respect to the density ratio is also found.