Regensburg 2000 – scientific programme

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TT: Tiefe Temperaturen

TT 1: Schwere Fermionen

TT 1.4: Invited Talk

Monday, March 27, 2000, 10:30–11:00, H20

Anomalous metallic states in stoichiometric f-electron compounds at ambient pressure — •O. Trovarelli, C. Geibel, C. Langhammer, S. Mederle, P. Hinze, P. Gegenwart, M. Grosche, M. Lang, G. Sparn, and F. Steglich — MPI-CPfS, Bayreuther Str. 40, 01187 Dresden

Among the f-electron compounds showing quantum critical behavior, YbRh₂Si₂ and CeNi₂Ge₂ belong to the selected group of materials in which strong non-Fermi-liquid effects are observed already at ambient pressure and in relatively clean samples. Their low-temperature electrical resistivity and electronic specific-heat coefficient show a nearly linear and a logarithmic temperature dependence, respectively, over a large temperature range, suggesting that they are very close to a magnetic instability. We study the evolution of the low-temperature properties of single-crystalline YbRh₂Si₂ using magnetic field and hydrostatic pressure as control parameters. Whereas the application of field leads to a gradual recovery of the properties of a heavy Landau Fermi-liquid, the application of moderate pressure (at zero field) induces anomalies in the electrical resistivity, indicating the onset of long-range magnetic order. In the case of CeNi₂Ge₂ we discuss recent results of a systematic study on various slightly off-stoichiometric Ce_{1± x}Ni_{2 ± y}Ge_{2∓ y} polycrystals, in terms of the composition dependence of the lattice parameters, the value of the residual resistivity and the occurrence of incipient superconductivity.