Berlin 2012 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 15: Correlated Electrons: Quantum Impurities, Kondo Physics 1

TT 15.4: Vortrag

Montag, 26. März 2012, 17:30–17:45, BH 334

Numerical Renormalization Group for the Partially Broken SU(3) Kondo Model: 2-Channel Kondo Fixed Point. — •Evaristus Fuh Chuo, Laszlo Borda, and Johann Kroha — Physikalisches Institut der Universität Bonn, Germany

We use the numerical renormalization group (NRG) to investigate the partially broken two-channel SU(3) Kondo model with conserved conduction electron spin, comprised of a quantum impurity with a unique ground state and an excited doublet of the SU(2) subgroup of SU(3). The model was proposed earlier by Arnold et al. [1] to describe rotational impurities in a metal, like hydrogen ions in the interstitial space of a lattice, in order to explain the conductance anomalies (zero-bias anomaly and conductance spikes) found by Ralph and Buhrman [2] in point contact spectroscopy on ultrasmall Cu point contacts. We find a downward renormalization of the excited state energy by the Kondo correlations in the SU(2) doublet. In a wide range of parameter values this stabilizes the two-channel Kondo fixed point, in full agreement with the earlier perturbative RG results of Arnold et al. [1]. We map out the phase diagram of the model in the parameter space of excited-state level spacing and of the Kondo couplings within the excited state doublet and between the impurity ground and excited states, respectively. The robustness of the model with respect to dynamical screening as well as to coupling to higher impurity excitations is discussed.

[1] M. Arnold, T. Langenbruch, and J. Kroha, Phys. Rev. Lett. 99, 186601 (2007).

[2] D. C. Ralph and R. A. Buhrman, Phys. Rev. Lett. 69, 2118 (2007).