Characteristics of diluted magnetic semiconductor nanostructures

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We have studied the effect of spins in quantum dots on the transport through them. Especially, many body effects caused by the dot spins are studied in detail.We performed experiments on the interference through spin states of electrons in a quantum dot (QD) embedded in an Aharonov-Bohm (AB) interferometer. We have picked up a spin-pair state, for which the environmental conditions are ideally similar. The AB amplitude is traced in a range of the gate voltage that covers the pair. The behavior of the asymmetry in the amplitude around the two Coulomb peaks agrees with the theoretical prediction that relates a spin-flip process in a QD to the quantum dephasing of electrons. These results constitute evidence of "partial coherence" due to an entanglement of spins in the QD and the interferometer.We observed the Fano-Kondo anti-resonance in a quantum wire with a side-coupled quantum dot In a weak coupling regime, dips due to the Fano effect appeared. As the coupling strentgh increased, cond … More uctance in the regions between the dips decreased alternately, showing the growth of the Kondo state. From the temperature dependence and the response to the magnetic field, we conclude that Ihe conductance reduction is due to the Fano-Kondo anti-resonance. At a Kondo valley with the Fano parameter q 0, the phase shift locking to Tr/2 against the gate voltage is observed when the system is close to the unitary limit in agreement with theoretical predictions.We observed huge (10000% at 0.07T) magnetoconductance (MC) in low temperature transport through an interface between a ferromagnetic semiconductor (Ga,Mn)As and a two-dimensional hole gas at a (Ga,A1)As/GaAs hetero-interface. The MC has a finite decay time and vanishes in a few seconds at 40mK while it rapidly recovers with a variation of magnetic field. The peculiar behavior is explained by the interplay between the Coulomb gap and disordered ferromagnetism. Sound evidence of the interpretation is obtained by introducing self-assembled InAs quantum dots at the interface, thus making the characteristic length of the disorder much longer Less