Does the attractive Hubbard model support larger persistent currents than the repulsive one ?

TL;DR

This study investigates how disorder and interaction type in a 1D Hubbard model affect persistent currents, revealing that repulsive interactions can lead to larger currents than attractive ones due to reduced local density fluctuations.

Contribution

It demonstrates that in disordered 1D Hubbard models, repulsive interactions produce larger persistent currents than attractive interactions, contrary to intuitive expectations.

Findings

Repulsive interactions yield larger persistent currents than attractive ones in disordered systems.

Local density fluctuations are suppressed by repulsive interactions, enhancing current.

Disorder influences the relationship between interaction type and persistent current magnitude.

Abstract

We consider a one-dimensional Hubbard model in the presence of disorder. We compute the charge stiffness for a mesoscopic ring, as a function of the size $L$, which is a measure of the permanent currents. We find that for finite disorder the permanent currents of the system with repulsive interactions are larger than those of the system with attractive interactions. This counter intuitive result is due to the fact that local density fluctuations are reduced in the presence of repulsive interactions.