From paramagnetic to diamagnetic charge and spin currents in a Hubbard necklace

We investigate persistent charge and spin currents in a Hubbard necklace driven by Aharonov-Bohm and Aharonov-Casher (AC) fluxes, respectively, by paying specific attention to the roles of interactions affecting the charge and spin sectors in different ways. Interacting electrons at half filling induce "diamagnetic" spin currents at lower AC fluxes whereas charge currents display paramagnetic responses for noninteracting electrons. We find that for systems away from half filling the characteristic roles of spin and charge currents are interchanged, that is, the charge currents exhibit a change from paramagnetic to diamagnetic currents, while the spin currents remain "paramagnetic" states.