[Zurück]

S. Hartmann, N. Oeschler, C. Krellner, C. Geibel, S. Paschen, F. Steglich:
"Thermopower evidence for an arupt Fermi surface change at the quantum critical point in YbRh₂Si₂";
Vortrag: International Conference on Magnetism 2009, ICM 2009, Karlsruhe, Germany; 26.07.2009 - 31.07.2009.

An unconventional quantum critical scenario with the breakdown of the local Kondo scale at an antiferromagnetic quantum critical point (QCP) has been claimed for YbRh2Si2. The predicted reconstruction of the Fermi surface (FS) upon crossing the QCP was evidenced by recent Hall-effect results. Here, we present low-temperature thermopower S(T) measurements of YbRh2Si2, performed to below 30 mK and in fields up to 1 T. In zero field, a logarithmic increase of S(T)/T is observed between 0.1 and 1 K. S(T)/T passes over a maximum at Tmax ≈ 100 mK and exhibits a sign change at T0 ≈ 30 mK with positive values in the zero-temperature limit. Tmax and T0 remain field independent, until both features suddenly vanish at the critical field Bc. For B > Bc, Fermi-liquid behavior is recovered as indicated by a constant S/T with negative values. The abrupt sign change of S/T(T → 0) at Bc provides clear evidence for a sudden FS reconstruction at the QCP of YbRh2Si2.