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

TL;DR

This study investigates the transition from single-ion to coherent non-Fermi liquid behavior in Ce$_{1-x}$La$_x$Ni$_9$Ge$_4$, revealing a crossover from local moment behavior to a coherent heavy fermion ground state.

Contribution

It provides the first detailed analysis of the crossover from single-ion to coherent non-Fermi liquid behavior in Ce$_{1-x}$La$_x$Ni$_9$Ge$_4$, highlighting the interplay between doping, specific heat, and resistivity.

Findings

CeNi$_9$Ge$_4$ has record-high electronic specific heat at low temperatures.

Doped samples show non-Fermi liquid behavior with logarithmic specific heat increase.

CeNi$_9$Ge$_4$ exhibits a coherent heavy fermion ground state at very low temperatures.

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 $\Delta c/T \approx$ 5.5 J $\rm K^{-2}mol^{-1}$ at $T=0.08$ K which was found in Cerium f-electron lattice systems. In the doped samples $\Delta c/T$ increases logarithmically in the temperature range between 3 K and 50 mK typical for non-Fermi liquid (nFl) behavior, while $\rho$ 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 $\Delta c/T$ 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.