Cooperative Ce and Yb valence fluctuations have recently been proposed as the mechanism responsible for stabilizing correlated electron phenomena in Ce${}_{1-x}$Yb${}_x$CoIn${}_5$ over an unexpectedly large range of concentrations. In order to better understand the origins and character of this stability, we have measured the effect of applied pressure on relevant energy scales such as the superconducting critical ($T_c$) and Kondo-lattice coherence ($T^{*}$) temperatures of Ce${}_{1-x}{R}_x$CoIn${}_5$ with $R=\text{Yb}$, Y, and Gd. Electrical resistivity measurements were performed under applied pressure on samples doped with intermediate-valent Yb and stable-valent Gd and Y, and the responses of $T_c$ and $T^{*}$ to increased pressure in these systems are compared. The character of $T_c\left(P\right)$ and $T^{*}\left(P\right)$ in Ce${}_{1-x}{R}_x$CoIn${}_5$ depends only on their respective ambient-pressure values $T_c\left(0\right)$ and $T^{*}\left(0\right)$, independent of the electronic configuration of $R$ or concentration $x$. The consequences of this result are discussed within the context of possible cooperative valence fluctuations in Ce${}_{1-x}$Yb${}_x$CoIn${}_5$.

• Received 3 July 2012

DOI:https://doi.org/10.1103/PhysRevB.86.100502