Novel Kondo anomaly in quantum dots

Abstract

Experimental observation of novel Kondo effects in quantum dots is reviewed with particular emphasis on the effect of magnetic field. The electronic configuration including spins in quantum dots can be modified by even a small magnetic field. We first use a vertical quantum dot with good tunability of orbital degeneracy in the few-electron regime but having a fixed tunnel coupling between the dot and leads. By tuning the spin configuration out of two electrons as a function of magnetic field, we observe a strong Kondo effect when the spin singlet and triplet are degenerate. This is due to the increased number of coherent co-tunneling processes. In the second we use a lateral quantum dot having good tunability of the tunnel coupling but some ambiguity in the electronic configuration. By adjusting both of the tunnel coupling and magnetic field, we observe the Kondo effect in the unitary limit. This is only observed in the presence of a small magnetic field, and can also be due to the change in the spin configuration.