Semiconductor quantum dots have been the subject of many studies in the last few years, in particular due to the possibility to manipulate single electronic states and single electronic spins. Most of the transport experiments have been performed on quantum dots defined by lithography on GaAs heterostructures, due to the high quality and the large tunability of these systems. However, other semiconductor materials could be more promising in terms of spin properties, in particular InAs due to its strong spin-orbit interaction and large g-factor.
We study electronic transport at low temperature in double quantum dots realized by top-gates on InAs nanowires [1]. This original and simple technique produces very high quality and fully tunable double quantum dots containing a small number of electrons [2]. The samples are characterized by transport spectroscopy at finite bias. For particular spin configurations in the double dot, it has been shown that the current can be suppressed due to the Pauli exclusion principle. We use this Pauli blockade spectroscopy to investigate spin relaxation mechanisms, as well as mixing of spin states, which will limit the spin coherence time in these systems.
While the hyperfine interaction with nuclear spins dominates the spin decoherence at weak inter-dot coupling and weak magnetic field, the effect of spin-orbit interaction becomes relevant at large coupling. More surprising is the regime of intermediate coupling: we show that the interplay between hyperfine interaction and spin-orbit coupling produces a bistable suppression of the leakage current in the spin blockaded region, which can be understood in terms of dynamic polarization of the nuclear spins [3].
[1] A. Pfund, I. Shorubalko, R. Leturcq and K. Ensslin, Appl. Phys. Lett. 89, 252106 (2006).
[2] I. Shorubalko, A. Pfund, R. Leturcq, M. T. Borgström, F. Gramm, E. Müller, E. Gini and K. Ensslin, Nanotechnology 18, 044014 (2007).
[3] A. Pfund, I. Shorubalko, K. Ensslin, R. Leturcq, cond-mat/0701054.
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