Regensburg 2000 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 7: Postersitzung I: Amorphe- und Tunnelsysteme (1-8), Mesoskopische Systeme (9-21), Schwere Fermionen (22-32), Kernmagnetismus (33-34), Josephson-Kontakte und SQUIDs (35-45), TT-Detektoren und Kryotechnik (46-49)
TT 7.23: Poster
Montag, 27. März 2000, 14:30–18:00, A
A non-magnetic Kondo effect in UAsSe and ThAsSe? A comparative study — •T. Cichorek1,2, Z. Henkie1, P. Gegenwart2, M. Lang2, A. Wojakowski1, and F. Steglich2 — 1Institute of Low Temperature and Structure Research, Polish Academy of Science, 50-950 Wroclaw 2, Poland — 2Max-Planck-Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
The upturn in the resistivity far below the ferromagnetic transition (TC=113K) in the metallic system UAsSe is rather unusual. A two-level-system, TLS, scenario [1], describing a non-magnetic Kondo effect seems to be likely on the bases of a crystallochemical analysis of uranium arsenoselenide revealing tunneling defects in the As/Se sublattice. On the other hand, if the hypothesis of the TLS model is true for UAsSe than the same scenario may also apply to its non-magnetic reference ThAsSe. Therefore, we have performed a comparative study of both compounds including specific-heat and resistivity measurements over the temperature range 1.5K−300K. The main results of the specific-heat measurements for UAsSe single crystals are that the Sommerfeld coefficient, γ, as well as the Debye temperature, ΘD, change with changing TC. The size of TC my serve as a measure of the degree of disorder in the As/Se sublattice. (γ = 22 mJ/mol · K2 and ΘD = 180K has been found for a crystal with TC=110K and γ = 41 mJ/mol · K2 and ΘD = 180K for a one with TC=116K ).We attribute the enhancement of the low-T specific heat of UAsSe to the effect of hybridization between 5f- and conduction-electron states. While the low-T specific-heat of UAsSe and ThAsSe (no measurable γ and sample independent ΘD=175K for the latter compound) show qualitative differences, only quantitative differences were found in their resistivities.
[1] D.L. Cox and A. Zawadowski, Adv. Phys. 47,599 (1998)