Enhanced Kondo effect via tuned orbital degeneracy in a spin 1/2 artificial atom

A strong Kondo effect is observed for a vertical quantum dot holding an odd number of electrons and spin 1/2 when an orbital degeneracy is induced by magnetic field. The estimated Kondo temperature for this doublet-doublet degeneracy is similar to that for the singlet-triplet degeneracy with an even electron number, indicating that a total of fourfold spin and orbital degeneracy accounts for the enhancement of the Kondo temperature. The experimental observation is qualitatively reproduced by scaling calculations using an SU(4) model at the orbital degeneracy.