Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 21: FS: Quantum Criticality in Strongly Correlated Metals

TT 21.4: Topical Talk

Wednesday, March 24, 2010, 11:40–12:20, H20

Interaction of the magnetic instability and the Fermi surface reconstruction in YbRh₂Si₂ — •Sven Friedemann¹, Tanja Westerkamp¹, Manuel Brando¹, Steffen Wirth¹, Niels Oeschler¹, Philipp Gegenwart^1,2, Cornelius Krellner¹, Christoph Geibel¹, Frank Steglich¹, Silke Bühler-Paschen³, Stefan Kirchner^4,5, and Qimiao Si⁵ — ¹MPI CPfS, Dresden, Germany — ²I. Physik. Institut, Georg-August-Universität, Göttingen, Germany — ³Institut für Festkörperphysik, TU Wien, Austria — ⁴MPI PKS, Dresden, Germany — ⁵Physics and Astronomy Department, Rice University, Houston, USA

An antiferromagnetic (AF) quantum critical point (QCP) is conventionally described by the quantum generalization of finite-temperature phase transitions. By contrast, the newly proposed unconventional scenarios for heavy-fermion metals are based on the breakdown of the Kondo effect. YbRh₂Si₂ is a prototype of the latter class. Here, we report high-precision Hall effect data demonstrating the coincidence of the Fermi surface reconstruction and the AF QCP in the stoichiometric compound. In addition, we present results revealing the global phase diagram of YbRh₂Si₂ under positive and negative chemical pressure as realized by Co and Ir substitution on the Rh side. Surprisingly, this leads to a detachment of the AF QCP from the Fermi surface reconstruction. In particular, negative pressure induces a separation of the two with an intermediate spin-liquid type ground state emerging in an extended field range. These results indicate a new quantum phase arising from the interaction of the Kondo breakdown and the AF QCP.