Spin and orbital fluctuations in non-equilibrium transport through quantum dots: A renormalisation-group analysis

TL;DR

This paper investigates non-equilibrium transport in a two-orbital quantum dot, revealing how orbital potential scattering influences conductance and occupation, with a focus on asymmetric couplings and magnetic field effects.

Contribution

It introduces a renormalisation-group analysis of a two-orbital Anderson model, highlighting the role of orbital potential scattering in non-equilibrium transport.

Findings

Identification of negative differential conductance regime

Observation of cascade resonance under magnetic field

Orbital potential scattering significantly alters conductance behavior

Abstract

We study non-equilibrium current and occupation probabilities of a two-orbital quantum dot. The couplings to the leads are allowed to be asymmetric and orbital dependent as it is generically the case in transport experiments on molecules and nanowires. Starting from a two-orbital Anderson model, we perform a generalised Schrieffer-Wolff transformation to derive an effective Kondo model. This generates an orbital potential scattering contribution which is of the same order as the spin exchange interaction. In a first perturbative analysis we identify a regime of negative differential conductance and a cascade resonance in the presence of an external magnetic field, which both originate from the non-equilibrium occupation of the orbitals. We then study the logarithmic enhancement of these signatures by means of a renormalisation-group treatment. We find that the orbital potential scattering qualitatively changes the renormalisation of the spin exchange couplings and strongly affects the differential conductance for asymmetric couplings.