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TT: Fachverband Tiefe Temperaturen

TT 19: Correlated Electrons: Quantum-Critical Phenomena

TT 19.7: Vortrag

Dienstag, 26. Februar 2008, 15:45–16:00, H 3010

Thermopower investigations of YbRh₂Si₂ in the vicinity of an antiferromagnetic quantum critical point — •Stefanie Hartmann, Niels Oeschler, Cornelius Krellner, Christoph Geibel, and Frank Steglich — Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany

The stoichiometric heavy-fermion compound YbRh₂Si₂ exhibits an antiferromagnetic (AFM) phase transition at an extremely low temperature of T_N = 72 mK. Upon applying a tiny magnetic field the AFM ordering is suppressed and the system is driven towards a quantum critical point (QCP). Furthermore, an additional energy scale at T^* indicating the crossover from local to itinerant character of the 4f electron vanishes at the QCP. Here, we report on measurements of the thermoelectric power S of high quality single crystals from 6 K down to 50 mK in fields up to 2 T. S(T) was measured within the easy ab plane of the system, that exhibits a critical field of only 50 mT. In the critical region S/T diverges upon approaching the QCP, while it exhibits a constant value in the Fermi liquid regime at higher fields. The low temperature behavior of the thermopower in YbRh₂Si₂ is discussed in detail and compared to available theoretical predictions. Whether the T^* line observed in Hall effect and magnetostriction measurements can also be resolved in the thermopower is a matter of great interest.