Nonequilibrium Zeeman-splitting in quantum transport through nanoscale junctions

TL;DR

This paper investigates how Zeeman splitting affects quantum transport through nanoscale junctions under nonequilibrium conditions, revealing different behaviors in weakly and strongly correlated regimes and identifying a crossover influenced by magnetic field strength.

Contribution

It provides a detailed analysis of Zeeman splitting in quantum dots out of equilibrium, highlighting the independence from asymmetries in the strongly correlated regime and describing the crossover behavior.

Findings

Zeeman splitting depends on lead asymmetry in weakly correlated regime.

In strongly correlated regime, the zero-bias anomaly position is independent of asymmetries.

A crossover from spin-fluctuation to charge fluctuation dominance with increasing magnetic field.

Abstract

We calculate the nonequilibrium differential conductance $G(V)$ through a quantum dot as function of bias voltage $V$ and applied magnetic field $H$. 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 coupling to the two leads, as well as on particle-hole asymmetry of the quantum dot. In contrast, in the strongly correlated regime, where Kondo-correlations dominate, the position $\Delta_K$ of the Zeeman-split zero-bias anomaly is independent of such asymmetries and always found to be of the order of the Zeeman energy $\Delta_0$. We find a crossover from the purely spin-fluctuation driven Kondo regime at small magnetic fields with $\Delta_K<\Delta_0$ to a regime at large fields where the contribution of charge fluctuations induces larger splittings with $\Delta_K>\Delta_0$ as it was observed in recent experiments.