Berlin 2008 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 32: Correlated Electrons: Poster Session

TT 32.9: Poster

Donnerstag, 28. Februar 2008, 14:00–18:00, Poster B

Kondo volume collapse and the Kondo breakdown transition in Heavy Fermions — •Andreas Hackl and Matthias Vojta — Institut für theoretische Physik, Universität zu Köln, Zülpicher Str. 77, 50937 Köln

The unconventional critical behavior near magnetic quantum phase transitions in various heavy-fermion metals, apparently inconsistent with the standard spin-density-wave scenario, has triggered proposals on the breakdown of the Kondo effect at the critical point. Here we investigate the fate of such a zero-temperature transition upon coupling of the electronic to lattice degrees of freedom. Specifically, we study a Kondo-Heisenberg model with volume-dependent Kondo coupling -- this model displays both Kondo volume collapse and Kondo-breakdown transitions, as well as a Lifshitz transition associated with a change of the Fermi-surface topology. Within a large-N treatment, we find that the Lifshitz transition tends to merge with the Kondo volume collapse and hence becomes first order, whereas the Kondo breakdown transition remains of second order except for very soft lattices. Interesting physics emerges at the quantum critical endpoint of the Kondo volume collapse: In two space dimensions, this endpoint is located at the Lifshitz line for a large range of parameters, thus two critical phenomena coincide without fine tuning. We briefly analyze the critical theory for such a situation, and finally relate our findings to current heavy-fermion experiments.