Regensburg 2007 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 11: Quantum Impurities, Kondo Physics
TT 11.6: Talk
Tuesday, March 27, 2007, 11:00–11:15, H19
Transconductance in a double quantum dot system in the Kondo regime — •Verena Koerting1, Jens Paaske2, and Peter Wölfle1 — 1Institut fuer Theorie der Kondensierten Materie, Universitaet Karslruhe, 76128 Karlsruhe, Germany — 2The Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
We consider a system of two lateral quantum dots in a spin 1/2 state, each contacted by two leads, and mutually coupled by spin exchange interaction K. The coupling to the leads is modeled by exchange tunneling (coupling J). We calculate the currents through both quantum dots as a function of the two bias voltages VL, R in renormalized perturbation theory in coupling functions J(ω), preserving the non-equilibrium physics at large voltages by taking into account the frequency dependence of the couplings. For sufficiently large antiferromagnetic K the groundstate of the double dot is a spin singlet. Since electron transport through e.g. the left dot requires triplet excitations we find a threshold in the differential conductance GL = dIL/dVL as a function of bias voltage VL, with GL ≈ 0 if eVL ≪ K and if the right dot is at low bias voltage e VR ≪ K. For increasing eVR approaching K the triplet states get occupied and GL rises rapidly. We will calculate this transconductance signal and show that Kondo correlations will significantly enhance dIL/dVR around e VR ≈ K. An outlook on experimental realization of this quantum transistor will be given.