Probing the fast dynamics of many-body correlated systems has been the subject of a long-standing research activity. By now, experimentalists have a variety of tools to study the equilibrium or close to equilibrium dynamics of bulk strongly correlated systems, which are thus better and better understood. On the other hand, much less is known about the fast dynamics of interacting many-body systems under out-ofequilibrium conditions. In this regard, nanoscale devices offer unique possibilities. Thanks to recent progress in nanotechnology, it is now feasible to design nanosystems in which correlated effects appear under out-ofequilibrium conditions. The Kondo effect in quantum dots constitutes in this respect a paradigmatic model system, where a single electron spin of the quantum dot is dynamically screened by the conduction electrons, leading to a many-body resonance for temperatures below the Kondo temperature TK. This effect has been studied extensively in transport and, more recently, by current fluctuation measurements. However, all previous studies focused exclusively on the low frequency limit, while the high frequency regime, i.e. the dynamics remained experimentally unexplored.
Figure A: Schematic picture of the superconducting circuit coupling the carbon nanotube (in orange) and the quantum detector (in red). A picture realised with a electronic microscope is also shown.
Figure B: Derivative of the current noise measured at two frequencies (in red) and theoretical predictions (in black). The singularity associated with the Kondo effect is pointed by the arrows. The blue curve corresponds to the conductance of the carbon nanotubes versus the voltage bias.
Thanks to the collaboration of experimentalist and theorist of Laboratoire de Physique des Solides, this regime has been probed and analysed. The first measurements of the high frequency current fluctuations of a carbon nanotube quantum dot in the Kondo regime has been realized by resonantly coupling it to an on-chip detector. A singularity in the noise related to Kondo effect appears for bias voltage V= hf/e when the frequency is of the order of kBTK/h. This singularity is strongly reduced when the frequency is close to 3 kBTK/h. These results are in good agreement with theoretical calculations provided that an additional spin decoherence rate is included. This detection scheme constitutes a new tool to probe the dynamics of correlated nanosystems.
J. Basset, A. Kasumov, P. Moca, G. Zarand, P. Simon, H. Bouchiat, R. Deblock. Phys. Rev. Lett. 108, 046802 (2012).
More info on web site of Mesoscopic Physics research team