Extracting the ground-state spin of a quantum dot from the conductance peaks in a parallel magnetic field at finite temperature

TL;DR

This paper presents a new method to accurately determine the ground-state spin of quantum dots from conductance measurements in a magnetic field, accounting for temperature effects and level crossings.

Contribution

It derives a closed-form expression for finite-temperature conductance considering exchange interaction and proposes an improved method for unambiguous spin determination.

Findings

Temperature can significantly affect peak motion at low temperatures.

Level crossings can lead to misidentification of ground-state spin.

The proposed method improves accuracy in spin determination.

Abstract

We derive a closed expression for the finite-temperature conductance of a Coulomb-blockade quantum dot in the presence of an exchange interaction and a parallel magnetic field. Parallel-field dependence of Coulomb-blockade peak position has been used to determine experimentally the ground-state spin of quantum dots. We find that for a realistic value of the exchange interaction, the peak motion can be significantly affected at temperatures as low as kT ~ 0.1 Delta, with Delta being the mean level spacing in the dot. This temperature effect can lead to misidentification of the ground-state spin when a level crossing occurs at low fields. We propose an improved method to determine unambiguously the ground-state spin. This method takes into account level crossings and temperature effects at a finite exchange interaction.