Interplay between the exchange and Coulomb interactions in a ferromagnetic semiconductor quantum dot

Abstract

We study the effects of the strong $sp\text{\ensuremath{-}}d$ exchange interaction, ferromagnetic ordering, and large spin fluctuations on quantum transport in a ferromagnetic semiconductor quantum dot (FSQD) coupled to nonmagnetic current leads. The retarded Green's function for a FSQD in the Coulomb blockade regime is calculated using a simple equation of motion technique. The dot level broadening due to $sp\text{\ensuremath{-}}d$ exchange interaction between the charge carrier spins and the localized magnetic moments of the magnetic atoms is considered within a self-consistent Born approximation. We also calculate the giant Zeeman splitting of the dot levels, the conductance, and the spin accumulation on the dot. The model predicts a large dot level broadening due to spin-disorder scattering, especially at temperatures close to the ferromagnetic ordering temperature. Our main finding is that in a small FSQD with a large intradot Coulomb repulsion the unusual temperature and magnetic field dependences of the level broadening give rise to a conductance behavior, which is similar to the Kondo resonance in QDs, even when the higher order correlations in the current leads are neglected.