Dresden 2009 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

TT: Fachverband Tiefe Temperaturen

TT 22: Correlated Electrons: Quantum-Critical Phenomena 2

TT 22.5: Vortrag

Mittwoch, 25. März 2009, 10:45–11:00, HSZ 03

Thermoelectric power in the quantum critical regime of YbRh₂Si₂ and CeNi₂Ge₂ — •Stefanie Hartmann, Niels Oeschler, Cornelius Krellner, Nubia Caroca-Canales, Christoph Geibel, and Frank Steglich — MPI CPfS, Dresden, Germany

The heavy-fermion compounds YbRh₂Si₂ and CeNi₂Ge₂ are situated very close to a quantum critical point (QCP). YbRh₂Si₂ exhibits an antiferromagnetic ground state with T_N = 70 mK and a tiny critical field B_c≈ 60 mT. In CeNi₂Ge₂ a non-magnetic ground state is observed. While in CeNi₂Ge₂ a 3-dim. spin-density wave scenario is realized, the QCP in YbRh₂Si₂ is shown to be of anomalous nature with a critical break-down of the Kondo scale. We report on low-temperature thermopower S(T) results in the quantum critical regimes of both compounds. S/T logarithmically diverges upon cooling down to 100 mK in the critical region of YbRh₂Si₂, reflecting the strongly diverging heavy quasi-particle mass upon approaching the QCP. However, a decrease and a sign change in S/T for B<B_c point toward a "small" Fermi surface on the magnetic side. In the quantum critical regime of CeNi₂Ge₂, S/T remains comparably small and does not exhibit a divergence for T→0. In the field-induced Landau-Fermi-liquid regime, both compounds exhibit a constant S/T below T_LFL as expected for a renormalized metal-like state.