Magnetic moments, pumping and spin polarization in ballistic nanoscopic circuits

Magnetic moments excited by currents in nanoscopic circuits containing loops are dominated by quantum effects and depend nonlinearly on exciting bias, at variance from classical expectations. The creation of a magnetic dipole by a bias-induced current can be reversed: i.e. connected rings excited by a time-dependent internal flux produce ballistic currents in the external wires even in the absence of an external bias. By studying the real-time quantum evolution of tight-binding models in different geometries, several kinds of crucial experimental tests of these ideas can be envisaged, resulting in potentially useful devices. As a direct consequence of the above mentioned nonlinearity, one can achieve, by employing suitable flux protocols, single-parameter nonadiabatic pumping. Next, we present several results that depend in an essential way on the spin magnetic interaction and study the conditions for a maximally spin polarized current. The effects of the spin-orbit interactions on the above thought experiments are explored.