Schedule Nov 21, 2002
YbRh2Si2: an unconventional metal
Frank Steglich, CPfS
www.cpfs.mpg.de/departments/physics/steglich-seite.html
Single crystals of the "heavy-fermion" metal YbRh2Si2 show pronounced non-Fermi-liquid (NFL) phenomena at p = 0 and B = 0. These are related to a weak antiferromagnetic (AF) transition at TN 70 mK. By doping with about 2 at% Ge, the Nel temperature is depressed to T 20 mK. For the Ge-doped single crystal the resistivity ? is found to depend linearly on temperature over almost three decades at T = 10 mK, reminiscent of the theoretical prediction for the frequently adopted spin-density-wave (SDW) scenario (assuming 2D AF spinfluctuations). The AF transition at 20 mK cannot be resolved in ?(T) because of the alloying-induced disorder causing a residual value of ?0 4.5 Ocm (compared to 1 Ocm for the pure compound). Recent results of magnetic and thermodynamic measurements are in striking conflict with the 2D SDW scenario. The disparate behaviors concerning the temperature dependences of both the electrical resistivity and the Sommerfeld coefficient of the electronic specific heat upon approaching the QCP indicate a break-up of the heavy ("composite") fermions.

In collaboration with: P. Gegenwart, J. Custers, N. Oeschler, Y. Tokiwa, H. Wilhelm, K. Neumaier, C. Geibel, G. Sparn, S. Mederle, C. Ppin and P. Coleman

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