Nonequilibrium Cotunneling through a Three-Level Quantum Dot

TL;DR

This paper models nonlinear cotunneling conductance in a three-level quantum dot using an effective Kondo model derived from a three-orbital Anderson model, predicting phenomena observable in current experiments.

Contribution

It introduces a generalized Schrieffer-Wolff transformation for a three-level quantum dot and calculates nonequilibrium occupation and cotunneling current, providing new theoretical insights.

Findings

Identification of inelastic cotunneling thresholds and their magnetic field splittings.

Qualitative agreement with experimental data on carbon nanotube and InAs quantum dots.

Predictions of cascade resonances and magnetic-field effects on orbital splitting.

Abstract

We calculate the nonlinear cotunneling conductance through a quantum dot with 3 electrons occupying the three highest lying energy levels. Starting from a 3-orbital Anderson model, we apply a generalized Schrieffer-Wolff transformation to derive an effective Kondo model for the system. Within this model we calculate the nonequilibrium occupation numbers and the corresponding cotunneling current to leading order in the exchange couplings. We identify the inelastic cotunneling thresholds and their splittings with applied magnetic field, and make a qualitative comparison to recent experimental data on carbon nanotube and InAs quantum-wire quantum dots. Further predictions of the model like cascade resonances and a magnetic-field dependence of the orbital level splitting are not yet observed but within reach of recent experimental work on carbon nanotube and InAs nanowire quantum dots.