Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 37: Correlated Electrons: Quantum Impurities, Kondo Physics
TT 37.3: Vortrag
Freitag, 29. Februar 2008, 10:45–11:00, H 2053
Stable Two-Channel Kondo Fixed Point of an SU(3) Quantum Defect in a Metal: Renormalization-Group Analysis and Conductance Spikes — •Katinka Ballmann, Tobias Langenbruch, Michael Arnold, and Johann Kroha — Physikalisches Institut, Universität Bonn, Germany
We propose a physical realization of the two-channel Kondo (2CK) effect, where a rotational defect in a metal has a unique ground state and twofold degenerate excited states [1]. In a wide range of parameters the interactions with the electrons renormalize the excited doublet downward below the bare defect ground state, thus stabilizing the 2CK fixed point. In addition to the Kondo temperature TK the three-state defect exhibits another low-energy scale, associated with ground-to-excited-state transitions, which can be exponentially smaller than TK. Using the perturbative nonequilibrium renormalization group we demonstrate that this can provide the long-sought explanation of the sharp conductance spikes observed by Ralph and Buhrman in ultrasmall metallic point contacts. In addition, we investigate the effect of an applied magnetic field coupling to the angular magnetic moment of the defect, lifting the degeneracy of the excited states, which can lead to a splitting of the sharp conductance spikes even when the Zeeman energy is less than TK.
[1] M. Arnold, T. Langenbruch, and J. Kroha, PRL 99, 18660 (2007).