Persistent currents from the competition between Zeeman coupling and spin-orbit interaction

We investigate the role that the spin degree of freedom plays in persistent current and show that Zeeman coupling induces persistent current as conventional Aharonov-Bohm (AB) flux does by competing with spin-orbit (SO) interaction. We demonstrate that, in the presence of SO interaction, Zeeman coupling and AB flux break time-reversal symmetry through intrinsically different mechanisms. A corresponding interesting observable effect for persistent current is generally found and explicitly computed for a symmetric mesoscopic ring with noninteracting electrons.