Novel Kondo anomaly in quantum dots

Experimental observation of novel Kondo effects in quantum dots is reviewed with particular emphasis on the effect of magnetic field. The electronic c onfiguration including spins in quantum dots can be modified by even a smal l 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 e ffect 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 tile tunnel coupling but som e ambiguity in the electronic configuration. By adjusting both of the tunne l coupling and magnetic field, we observe the Kondo effect in the unitary l imit. This is only observed in the presence of a small magnetic field, and can also be due to the change in the spin configuration. (C) 2001 Elsevier Science B.V. All rights reserved.