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

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 $kT\ensuremath{\sim}0.1\ensuremath{\Delta}$, where $\ensuremath{\Delta}$ is 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 in the presence of interactions.