A BCS Gap on the Lattice

TL;DR

This paper reports Monte Carlo simulations of the 3+1D NJL model at high baryon density, demonstrating a BCS superfluid gap formation characterized by particle-hole mixing and a measurable energy gap.

Contribution

It provides the first evidence of a BCS gap and superfluidity in the NJL model on the lattice through detailed fermion propagator analysis.

Findings

Evidence of particle-hole mixing near the Fermi surface

Observation of a non-zero energy gap Delta>0

Ratio of BCS gap to vacuum quark mass is approximately 0.15

Abstract

Monte Carlo simulations of the 3+1 dimensional NJL model are performed with baryon chemical potential mu>0. For mu>Sigma_0, the constituent quark mass in vacuum, chiral symmetry is restored and a diquark condensate <qq_+> forms. We analyse the fermion propagator and find evidence for particle-hole mixing in the vicinity of the Fermi surface and an energy gap Delta>0, both of which provide evidence for superfluidity at high baryon density induced by a BCS mechanism. At (mu a)=0.8 the ratio between the BCS gap and the vacuum quark mass is Delta/Sigma_0=0.15(2).