Spin filling in quantum dots

Abstract

In this chapter we investigate the electronic transport through a Coulomb-blockaded quantum dot in which interactions are rather strong, in contrast to the ring structure discussed before. In this dot, which is based on the two-dimensional electron gas in a parabolic quantum well, spin states have been identified in the weak-, intermediate- and strong-coupling regime of the dot to the leads. We observe linear changes in conductance peak spacings with in-plane magnetic field in all regimes, which can be interpreted in terms of a Zeeman splitting of single-particle levels. This allows one to follow the sequence of ground-state spin of the quantum dot as individual electrons are added. A perpendicular magnetic field applied to the dot in the same state allows the investigation of spin-pair candidates under conditions where orbital effects dominate the evolution of conductance peaks. Strong correlations in the position and in the amplitude of neighboring peaks allow the final identification of spin-pairs. The method of combining parallel and perpendicular magnetic fields for identifying spin states and spin-pairs works well for all coupling strengths of dot states to the leads, indicating that the spin degree of freedom is remarkably stable.