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Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 30: Correlated Electrons: Quantum Impurities, Kondo Physics

TT 30.8: Talk

Tuesday, March 12, 2013, 11:30–11:45, H21

2-channel Kondo fixed point without fine tuning in a 3-level SU(3) quantum impurity: NRG results — •Evaristus Fuh Chuo, Katinka Ballmann, Laszlo Borda, and Johann Kroha — Physikalisches Institut, Universität Bonn

The 2-channel Kondo (2CK) effect with its exotic ground state properties has remained difficult to realize in physical systems. At low energies, a quantum impurity with orbital degree of freedom, like a proton bound in an interstitial lattice space, comprises a 3-level system with a unique ground state and (at least) doubly degenerate rotational excitations with excitation energy Δ. When immersed in a metal, electronic angular momentum scattering induces transitions between any two of these levels (couplings J), while the electron spin is conserved. We show by extensive NRG calculations that without fine-tuning of parameters this system exhibits a 2CK fixed point, due to Kondo correlations in the excited-state doublet whose degeneracy is stabilized by the the host lattice parity, while the channel symmetry (electron spin) is guaranteed by time reversal symmetry. We find a pronounced plateau in the entropy at S(TK<T<Δ)=kBln2 between the high-T value, S(T≫Δ)=kBln3, and the 2CK ground state value, S(0)=kBln√2. This indicates a down-renormalization of the doublet below the non-interacting ground state, thus realizing the 2CK fixed point, in agreement with earlier conjectures [1]. We map out the phase diagram in the J–Δ plane and compare with analytical results. TK shows non-monotonic J-dependence, characteristic for 2CK systems.
[1] M. Arnold, T. Langenbruch, J. Kroha, PRL 99, 186601 (2007)

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