Flow Equations for the BCS-BEC Crossover

TL;DR

This paper employs the functional renormalisation group to analyze the BCS-BEC crossover in ultracold fermionic gases, revealing how universal behavior and effective bosonic theories emerge across different phases.

Contribution

It introduces a unified flow equation approach that captures the entire phase diagram of the BCS-BEC crossover, highlighting the emergence of composite bosonic states.

Findings

Universality and effective bosonic theories emerge in the BEC limit and near critical temperature.

The flow equations provide a unified description of the phase diagram.

Different effective physics are reflected at various scales.

Abstract

The functional renormalisation group is used for the BCS-BEC crossover in gases of ultracold fermionic atoms. In a simple truncation, we see how universality and an effective theory with composite bosonic di-atom states emerge. We obtain a unified picture of the whole phase diagram. The flow reflects different effective physics at different scales. In the BEC limit as well as near the critical temperature, it describes an interacting bosonic theory.