Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 11: Quantum Impurities, Kondo Physics

TT 11.4: Vortrag

Dienstag, 27. März 2007, 10:15–10:30, H19

2-channel Kondo behavior in quantum defects with partially broken SU(3) symmetry — •Tobias Langenbruch, Michael Arnold, and Johann Kroha — Physikalisches Institut, Universität Bonn, Germany

We propose an atomic rotational state defect embedded in a metal as a microscopic model to realize the 2-channel Kondo (2CK) effect. The model has a partially broken SU(3) symmetry, where the excited states of the bare defect are doubly degenerate due to space inversion symmetry.

Using perturbative renormalization group techniques we show that for a wide range of parameters this model has a stable two-channel Kondo fixed point. The stability is due to a correlation-induced crossing of the local levels. The energy dependence of the renormalized coupling functions is crucial for this stabilization.

We calculate the differential conductance of quantum point contacts with such defects, exhibiting spikes at elevated bias voltages due to fluctuations into excited local levels. We discuss the various energy scales involved in this system as well as the asymmetrical spike shape and conjecture that this model may provide a microscopic explanation for the longstanding puzzle of both, the 2CK signatures and the conductance spikes observed by Ralph and Buhrman [1] in ultrasmall quantum point contacts.

[1] D.C. Ralph and R. A. Buhrman, PRL 69, 2118 (1992); PRB 51, 3554 (1995).