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MA: Fachverband Magnetismus

MA 10: Thyssen-Krupp Electrical Steel Ph. D. Thesis Award (Dissertationspreis)

MA 10.4: Invited Talk

Monday, March 7, 2016, 16:15–16:40, H32

Thermal Transport in Strongly Correlated Rare Earth Intermetallic Compounds — •Heike Pfau — Stanford Institute for Materials and Energy Sciences SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA

Heavy fermion materials are characterized by strong electronic inter- actions and small energy scales, which can be tuned by applying a magnetic field. In YbRh2Si2, such a tuning leads to novel phenomena both at very small magnetic fields and at higher fields.

At small fields of 60 mT, YbRh2Si2 undergoes a quantum phase transition with unconventional properties, the origin of which are heavily debated and an established microscopic theory is still missing. With the help of the Wiedemann-Franz law, we investigated if such a theory can be formulated in the framework of quasiparticles. While we found it to be valid away from the quantum critical point, our analysis directly at the quantum critical point reveals a violation of the Wiedemann-Franz law. A violation would imply the breakdown of the quasiparticle concept.

At high magnetic fields of 10 T, a transition was reported, for which two scenarios were proposed: a Lifshitz transition or a sudden break-down of the Kondo effect. Using thermopower and resistivity measurements, we detected not one but in total three transitions in higher fields. The extraordinary agreement of our and previous experimental results with renormalized bandstructure calculations enabled us to explain the development of YbRh2Si2 in higher magnetic fields as an interplay of a smooth Kondo suppression and three Lifshitz transitions.