Modulation of three‐orbital Kondo effect in quantum dots

We study the orbital Kondo effect due to two electrons occupying three orbital levels in quantum dot (QD) systems. By applying the non-crossing approximation to the three-orbital Anderson impurity model, we calculate the conductance and the thermopower. We consider the realistic situation in QD systems, where the correlation effect induces the orbital-level splitting even at zero field. It is found that the level splitting at zero field larger than temperature revives the maximum structure in the conductance clearly, which characterizes the singlet-triplet Kondo effect. We also show that the enhancement of the Kondo temperature due to the singlet-triplet mechanism gives rise to the characteristic behavior in the thermopower as well. This is in contrast with the two-orbital case, where the thermopower is zero irrespective of the level splitting. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)