抄録
The Kondo effect associated with state degeneracy is studied for a two-dimensional harmonic quantum dot. State degeneracies between a spin singlet and triplet states, between two spin doublet states, and between a spin doublet and quadruplet states are induced by magnetic field. For the first two degenracies, strong enhancement of the Kondo effect is observed. The estimated Kondo temperature for the “doublet–doublet” degeneracy with an odd electron number is similar to that for the “singlet–triplet” degeneracy with an even electron number, indicating that a total of four-fold spin and orbital degeneracy for both cases accounts for the similar enhancement of the Kondo temperature. The Kondo effect generally gives rise to enhanced conductnace and a zero-bias peak of differential conductance in the Coulomb valley. In contrast, enhacned conductance but a zero-bias dip is observed for the third “doublet–quadruplet” degeneracy. This can be due to Zeeman splitting but no clear interpretation is reached yet.
