Coulomb-Blocked Transport Through a Quantum Dot with Spin-Split Level: Increase of Differential Conductance Peaks by Spin Relaxation

TL;DR

This paper develops a non-perturbative method to analyze non-equilibrium transport in a spin-split quantum dot, revealing how spin relaxation influences conductance peaks in cotunneling regimes.

Contribution

It introduces a physically consistent, perturbative solution across the entire Coulomb diamond for quantum dot transport with spin relaxation effects.

Findings

Conductance peaks are maximized when spin relaxation rate matches sequential tunneling rate.

The method smoothly transitions between different tunneling regimes within the Coulomb diamond.

Results can be extended to multi-level quantum dot systems.

Abstract

Non-equilibrium transport through a quantum dot with one spin-split single-particle level is studied in the cotunneling regime at low temperatures. The Coulomb diamond can be subdivided into parts differing in at least one of two respects: what kind of tunneling processes (i) determine the single-particle occupations and (ii) mainly contribute to the current. No finite systematic perturbation expansion of the occupations and the current can be found that is valid within the entire Coulomb diamond. We therefore construct a non-systematic solution, which is physically correct and perturbative in the whole cotunneling regime, while smoothly crossing-over between the different regions. With this solution the impact of an intrinsic spin-flip relaxation on the transport is investigated. We focus on peaks in the differential conductance that mark the onset of cotunneling-mediated sequential transport. It is shown that these peaks are maximally pronounced at a relaxation roughly as fast as sequential tunneling. The approach as well as the presented results can be generalized to quantum dots with few levels.