Berlin 2015 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 102: Transport: Quantum Dots, Quantum Wires, Point Contacts 2 (jointly with HL)
TT 102.5: Talk
Thursday, March 19, 2015, 16:00–16:15, A 053
Non-equilibrium Renormalization Group for Kondo Qdots in a Microwave Photon Field — •Andisheh Khedri1,2,3, Ammar Nejati1, and Johann Kroha1 — 1Universität Bonn — 2RWTH Aachen — 3FZ Jülich
Recent experiments on Kondo quantum dots in a static magnetic field and a microwave photon field show a resonant enhancement of the zero-bias differential conductance at a photon energy which scales with the applied magnetic field, but which is substantially larger than the bare Zeeman energy of the dot levels [1]. This behavior cannot be explained by direct, photoinduced spin-flip excitations of the dot. It points to a strong renormalization of the Zeeman energy (Landé factor) in the presence of the microwave field. We propose that the observed resonant conductance is caused by photo-assisted Kondo spin-flip scattering of the lead electrons, i.e., by electronic lead–dot transitions, assisted by coherent photon absorption and/or emission. We develop the non-equilibrium perturbative renormalization group (RG) theory [2] for this problem. The renormalization of the various coupling functions for spin vertices without photon processes as well as involving photon absorption, emission and scattering is anaylzed as well as the Qdot level shifts. We find a subtle interplay between Kondo scattering and coherent photoassisted processes, restoring the logarithmic RG flow and leading to strong renormalization of the Landé factor.
[1] B. Hemingway, S. Herbert, M. Melloch, A. Kogan, PRB 90, 125151 (2014)
[2] A. Rosch, J. Paaske, J. Kroha, P. Wölfle, PRL 90, 076804 (2003).