Evidence of a heavy fermion state in the disordered Ce-alloy system without translation symmetry

Abstract

We have measured the specific heat ${C}_{p}$ and the resistivity $\ensuremath{\rho}$ on sputtered amorphous ${\text{Ce}}_{x}{\text{Y}}_{80\ensuremath{-}x}{\text{Mn}}_{20}$ alloys. The low-temperature specific heat has been found to follow ${C}_{p}=\ensuremath{\gamma}T+\ensuremath{\beta}{T}^{3}$ for all the samples. The $T$-linear coefficient $\ensuremath{\gamma}$ increases linearly with increasing Ce concentration and becomes very large $(\ensuremath{\gamma}>100\text{ }\text{mJ}\text{ }{\text{mol}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2})$ in the Ce-rich region. The ${\ensuremath{\gamma}}_{\text{Ce}}$ per Ce atom is about $200\text{ }\text{mJ}\text{ }{\text{Ce-mol}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2}$ and almost independent of the Ce concentration. The large ${\ensuremath{\gamma}}_{\text{Ce}}$ has been interpreted in terms of the electronic specific heat owing to the $4f$-electron mixed with conduction electrons. In the resistivity $\ensuremath{\rho}$, the $\ensuremath{-}\text{log}\text{ }T$ dependence has been observed at low temperature for $x\ensuremath{\ge}51$, which suggests the formation of the dense Kondo state. The $\ensuremath{\rho}$ vs $T$ for $x\ensuremath{\ge}62$ exhibits a maximum and decreases as $\ensuremath{\rho}\ensuremath{\propto}A{T}^{2}$ with a large coefficient $A$ down to the low-temperature limit. These results suggest the formation of a heavy fermion state as the ground state for $x\ensuremath{\ge}62$. We made the Kadowaki-Woods (KW) plot for $x\ensuremath{\ge}62$ and found the $A/{\ensuremath{\gamma}}^{2}$ value to be much smaller than that of the conventional KW relation probably due to the $f$-orbital degeneracy.