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TT: Fachverband Tiefe Temperaturen

TT 4: CE: Quantum-Critical Phenomena 1

TT 4.8: Talk

Monday, March 14, 2011, 12:30–12:45, HSZ 201

Violation of the Wiedemann-Franz law at the Quantum Critical Point of YbRh₂Si₂ — •Stefanie Hartmann¹, Cornelius Krellner¹, Stefan Kirchner², Ulrike Stockert¹, Christoph Geibel¹, and Frank Steglich¹ — ¹MPI CPfS, Nöthnitzer Str. 40, 01187 Dresden — ²MPI PKS, Nöthnitzer Str. 38, 01187 Dresden

The prototype heavy-fermion system YbRh₂Si₂ appears to be situated extremely close to an antiferromagnetic (AF) quantum critical point (QCP). Besides the disappearance of the AF ordering (T_N = 70 mK) at a tiny critical magnetic field, B_c≈ 60 mT, applied perpendicular to the tetragonal c axis, the breakdown of the Kondo scale accompanied by an abrupt Fermi surface reconstruction is assumed to take place at the very same field. Beyond B_c a heavy Landau Fermi-liquid (FL) phase emerges.

We have studied the thermal conductivity κ(T,B) as well as the electrical resistivity ρ(T,B) in a wide temperature and field range (T≥ 30 mK, B≤ 1 T) using the same YbRh₂Si₂ single crystalline sample for both measurements. The comparison of both quantities evidences that, in the limit T=0, the Wiedemann-Franz law, κρ=L₀T, is fulfilled deep inside the AF phase as well as in the FL regime of YbRh₂Si₂. The universal relation between heat and charge conduction is, however, distinctly violated upon approaching the field-induced QCP from either side, caused by the emergence of a novel type of inelastic small-angle scattering processes.