Persistent Currents in Interacting Systems: Role of the Spin

TL;DR

This study examines how electron-electron interactions and spin influence persistent currents in disordered mesoscopic rings, revealing that interactions can either suppress or enhance specific current harmonics depending on the model.

Contribution

It demonstrates the contrasting effects of interactions on persistent current harmonics in Hubbard and spinless fermion models using self-consistent Hartree-Fock methods.

Findings

Second harmonic suppressed in spinless fermions due to interactions

Second harmonic enhanced in Hubbard model due to interactions

Charge density fluctuations correlate with harmonic modifications

Abstract

Persistent currents flowing through disordered mesoscopic rings threaded by a magnetic flux are investigated. Models of fermions with on-site interactions (Hubbard model) or models of spinless fermions with nearest neighbor interactions are considered on 2D cylinders with twisted boundary conditions in one direction to account for a magnetic flux. Self-consistent Hartree-Fock methods are used to treat the electron-electron interaction beyond first order. We show that the second harmonic of the current (which is relevant in the diffusive regime) is {\it strongly suppressed} by the interaction in the case of spinless fermions while it is {\it significantly enhanced} in the Hubbard model. Our data also strongly suggest that the reduction (increase) of this harmonic is related to a strong increase (reduction) of the spacial fluctuations of the charge density.