BCS-BEC Crossover Effects and Pseudogap in Neutron Matter

TL;DR

This paper explores the BCS-BEC crossover in neutron matter, highlighting pseudogap phenomena and the impact of strong interactions on spectral functions and critical temperature behavior.

Contribution

It generalizes T-matrix theory to finite-range interactions in neutron matter and analyzes pseudogap effects and quasiparticle weight reductions.

Findings

Spectral function shows pseudogap above T_c in strong coupling.

Reduced quasiparticle weight may significantly influence T_c.

Density dependence of T_c is weak despite correlations.

Abstract

Due to the large neutron-neutron scattering length, dilute neutron matter resembles the unitary Fermi gas, which lies half-way in the crossover from the BCS phase of weakly coupled Cooper pairs to the Bose-Einstein condensate of dimers. We discuss crossover effects in analogy with the T-matrix theory used in the physics of ultracold atoms, which we generalize to the case of a non-separable finite-range interaction. A problem of the standard Nozieres-Schmitt-Rink approach and different ways to solve it are discussed. It is shown that in the strong-coupling regime, the spectral function exhibits a pseudo-gap at temperatures above the critical temperature T_c. The effect of the correlated density on the density dependence of T_c is found to be rather weak, but a possibly important effect due to the reduced quasiparticle weight is identified.