Numerical renormalization group studies of SU(4) Kondo effect in quantum dots

We theoretically study an enhancement of the Kondo effect in quantum dots with two orbitals and spin 12. The Kondo temperature and conductance are evaluated as functions of energy difference Δ between the orbitals, using the numerical renormalization group method. The Kondo temperature is maximal around the degeneracy point (Δ=0) and decreases with increasing |Δ| following a power law, TK(Δ)=TK(0)(TK(0)/|Δ|)γ, which is consistent with the scaling analysis. The conductance at T=0 is almost constant 2e2/h. Both the orbitals contribute to the conductance around Δ=0, whereas the current through the upper orbital is negligibly small when |Δ|≳TK(0). These are characteristics of SU(4) Kondo effect.