Renormalization of the BCS-BEC crossover by order parameter fluctuations

TL;DR

This paper employs a functional renormalization group method with partial bosonization to analyze how order parameter fluctuations influence the BCS-BEC crossover in three-dimensional superfluid fermions, providing detailed calculations at the unitary point.

Contribution

It introduces a new truncation scheme for the vertex expansion using Dyson-Schwinger equations, linking the superfluid order parameter to the single particle gap via a Ward identity.

Findings

Calculated chemical potential, gap, and order parameter at unitarity

Results agree with experimental data and previous theories

Demonstrates the importance of order parameter fluctuations in the crossover

Abstract

We use the functional renormalization group approach with partial bosonization in the particle-particle channel to study the effect of order parameter fluctuations on the BCS-BEC crossover of superfluid fermions in three dimensions. Our approach is based on a new truncation of the vertex expansion where the renormalization group flow of bosonic two-point functions is closed by means of Dyson-Schwinger equations and the superfluid order parameter is related to the single particle gap via a Ward identity. We explicitly calculate the chemical potential, the single-particle gap, and the superfluid order parameter at the unitary point and compare our results with experiments and previous calculations.