Effect of Pressure on Superconductivity and the Kondo-Lattice Coherence Temperature in Ce$_{1-x}R_x$CoIn$_5$ with $R$ = Yb, Y, Gd*

Generally, rare-earth substitution for Ce in the heavy fermion superconductor CeCoIn$_5$ suppresses superconductivity rapidly. However, it was recently reported that the correlated electron ground state of Ce$_{1-x}$Yb$_x$CoIn$_5$ is stabilized over an anomalously large range in $x$, perhaps because of cooperative valence fluctuations of the Ce and Yb ions. Motivated by this possibility, we studied the effect of applied pressure on the superconducting critical ($T_c$) and Kondo-lattice coherence ($T^*$) temperatures of Ce$_{1-x}R_x$CoIn$_5$ with $R$ = Yb, Y, and Gd in order to compare the effect of Yb substitution with other magnetic and non-magnetic rare-earth ion substitutions. We performed electrical resistivity measurements under pressures up to a maximum of $\sim$2.3 GPa in a piston-cylinder clamped high pressure cell using a 50:50 mixture of $n$-pentane and isoamyl alcohol for the pressure transmitting medium. It was found that the variations of $T_c$ and $T^*$ in Ce$_{1-x}R_x$CoIn$_5$ under pressure were approximately independent of $R$. This result implies that the effect of pressure is independent of the magnetic configuration of the rare-earth ion being introduced.