Orbital and spin contributions to thegtensors in metal nanoparticles

We present a theoretical study of the mesoscopic fluctuations of g tensors in a metal nanoparticle. The calculations were performed using a semirealistic tight-binding model, which contains both spin and orbital contribution to the g tensors. The results depend on the product of the spin-orbit scattering time τₛₒ and the mean-level spacing δ, but are otherwise weakly affected by the specific shape of a generic nanoparticle. We find that the spin contribution to the g tensors agrees with random matrix theory (RMT) predictions. On the other hand, in the strong spin-orbit coupling limit δτₛₒ/→0, the orbital contribution depends crucially on the space character of the quasiparticle wave functions: it levels off at a small value for states of d character but is strongly enhanced for states of sp character. Our numerical results demonstrate that when orbital coupling to the field is included, RMT predictions overestimate the typical g factor of orbitals that have dominant d-character. This finding points to a possible source of the puzzling discrepancy between theory and experiment.