Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 6: Postersession Correlated Electrons: (General) Theory, Low-Dimensional Systems, Kondo Physics, Heavy Fermions, Quantum-Critical Phenomena

TT 6.51: Poster

Montag, 23. März 2009, 13:00–16:45, P1A

Interplay between crystal-field splitting and Kondo-effect in CeNi₉Ge_4−xSi_x. — Christian Gold¹, Ludwig Peyker¹, •Ernst-Wilhelm Scheidt¹, Wolfgang Scherer¹, and Herwig Michor² — ¹Institut für Physik, Universität Augsburg, 86159 Augsburg, Germany — ²Institut für Festkörperphysik, TU Wien, 1040 Wien, Austria

CeNi₉Ge₄ exhibits a Kondo lattice behavior with unusual single-ion non-Fermi-lquid features and with the largest ever recorded value of the electronic specific heat Δ C/T≈5.5 J/mol K² without showing any trace of magnetic order. An entropy calculation yielding S = Rln4 at T < 20 K suggests that in CeNi₉Ge₄ a crystal electrical field (CEF) ground state quasi quartet of Ce³⁺ splits into two doublets leading to an interplay between Kondo effect and CEF splitting on the same energy scale. CeNi₉Si₄ is a Kondo lattice system with an enhanced Sommerfeld coefficient of γ ≈ 155 mJ/mol K² which can be well described by the degenerate Coqblin-Schrieffer model (J =5/2). Here we report on specific heat, susceptibility and resistivity measurements of the substitution series CeNi₉Ge_4−xSi_x which i) exhibits a continuous crossover from a four-folder CEF ground state to a two folder one in present of Kondo screening for x = 0.5 - 4 and which ii) follows a reduction of the Kondo temperature T_K with decreasing lattice volume between x = 0 and 0.1, which is in contrast to the compressible Kondo lattice model.