Crossover from Single-Ion to Coherent Non-Fermi Liquid Behavior in Ce${}_{1-x}$La${}_x$Ni${}_9$Ge${}_4$

Abstract

We report specific heat and magneto-resistance studies on the compound Ce${}_{1-x}$La${}_x$Ni${}_9$Ge${}_4$ for various concentrations over the entire stoichiometric range. Our data reveal single-ion scaling with Ce-concentration between $x=0.1$ and 0.95. Furthermore, CeNi${}_9$Ge${}_4$ turns out to have the largest ever recorded value of the electronic specific heat $\hat{I}”c/T\approx$ 5.5 J ${\mathrm{K}}^{-2}\mathrm{mo}{\mathrm{l}}^{-1}$ at $T=0.08$ K which was found in Cerium f-electron lattice systems. In the doped samples $\hat{I}”c/T$ increases logarithmically in the temperature range between 3 K and 50 mK typical for non-Fermi liquid (nFl) behavior, while $\ddot{I}$ exhibits a Kondo-like minimum around 30 K, followed by a single-ion local nFl behavior. In contrast to this, CeNi${}_9$Ge${}_4$ flattens out in $\hat{I}”c/T$ below 300 mK and displays a pronounced maximum in the resistivity curve at 1.5 K indicating a coherent heavy fermion groundstate. These properties render the compound Ce${}_{1-x}$La${}_x$Ni${}_9$Ge${}_4$ a unique system on the borderline between Fermi liquid and nFl physics.

2 pages, 3 figures, SCES04