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Authors: Katinka Ballmann, Michael Arnold, Tobias Langenbruch and Johann Kroha
As a physical realization of the two-channel Kondo (2CK) effect a model has been proposed, where a dynamical defect in a metal has a unique ground state and twofold degenerate excited states [1]. It was found that 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 the three-state defect exhibits another low-energy scale, associated with ground-to-excited-state transitions, which can be exponentially smaller than the Kondo temperature. Using the perturbative nonequilibrium renormalization group it was demonstrated that this can provide the long-sought explanation of the sharp conductance spikes observed by Ralph and Buhrman in ultrasmall metallic point contacts. Here we investigate the effect of an applied magnetic field, which lifts the degeneracy of the excited states, on the nonequilibrium differential conductance. It can lead to a splitting of the conductance spikes even for Zeeman energies smaller than the Kondo temperature, as observed experimentally. [1] M. Arnold, T. Langenbruch, and J. Kroha, PRL 99, 186601 (2007) |
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