Nonequilibrium Zeeman splitting in quantum transport through nanoscale junctions.

We calculate the differential conductance G(V) through a quantum dot in an applied magnetic field. We use a Keldysh conserving approximation for weakly correlated and the scattering-states numerical renormalization group for the intermediate and strongly correlated regime out of equilibrium. In the weakly correlated regime, the Zeeman splitting observable in G(V) strongly depends on the asymmetry of the device. In contrast, in the strongly correlated regime the position Δ(K) of the Zeeman-split zero-bias anomaly is almost independent of such asymmetries and of the order of the Zeeman energy Δ(0). We find a crossover from the purely spin-fluctuation driven Kondo regime at small magnetic fields with Δ(K)<Δ(0) to a regime at large fields where the contribution of charge fluctuations induces larger splittings with Δ(K)>Δ(0) as it was observed in recent experiments.