title: Quantum rings in magnetic fields and spin current generation.
abstract: We propose three different mechanisms for pumping spin-polarized currents in a ballistic circuit using a time-dependent magnetic field acting on an asymmetrically connected quantum ring at half filling. The first mechanism works thanks to a rotating magnetic field and produces an alternating current with a partial spin polarization. The second mechanism works by rotating the ring in a constant field; like the former case, it produces an alternating charge current, but the spin current is dc. Both methods do not require a spin-orbit interaction to achieve the polarized current, but the rotating ring could be used to measure the spin-orbit interaction in the ring using characteristic oscillations. On the other hand, the last mechanism that we propose depends on the spin-orbit interaction in an essential way, and requires a time-dependent magnetic field in the plane of the ring. This arrangement can be designed to pump a purely spin current. The absence of a charge current is demonstrated analytically. Moreover, a simple formula for the current is derived and compared with the numerical results.
authors.affiliation: Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Rome, Italy. Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Frascati, Via E. Fermi 40, I-00044 Frascati, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Cini
authors.forename: Stefano
authors.initials: S
authors.lastname: Bellucci
mesh_terms: D060526:Magnetic Fields; D008956:Models, Chemical; D011789:Quantum Theory