Superconductivity and non-Fermi-liquid behavior in Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$*

Single-crystals of Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$ were investigated by specific heat $C_{\rm P}(T)$, electrical resistivity $\rho(T)$, and magnetic susceptibility $\chi(T)$ measurements as a function of $x$. As Yb is substituted for Ce, $T_{c}(x)$ is gradually suppressed to 0.9 K at $x=0.8$. In the low Yb concentration region near $x = 0.1$, there is a feature in the lattice constants and residual resistivity, a crossover in the anisotropy of $\chi(T)$, the development of NFL $T$-dependences of $\chi(T)$ and $C_{\rm P} (T)$ in the normal state,indicating the existence of a quantum critical point, and a plateau in $T_c(x)$. In the high Yb concentration region near $x=0.8$, there is an abrupt drop in the lattice parameters that is accompanied by a precipitous drop in $T_c(x)$. The features in the physical properties at $x=0.1$ and $0.8$ indicate the occurrence of some incipient electronic phase transitions, possibly involving the Ce and Yb valences at these compositions.