Nov 21, 2002
YbRh2Si2: an unconventional metal
Frank Steglich, CPfS
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 Néel 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 µOcm (compared to 1 µOcm 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. Pépin and P.
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