Evolution of the superconducting properties of CeCoIn$_5$ with Yb substitution

We report on the evolution of the physical properties of the Yb substitution series starting from the unconventional superconductor (SC) CeCoIn$_5$ to the isostructural normal metal YbCoIn$_5$. This study was motivated by the recent results of Cd or Hg substitution at the percentage level on the In site in CeCoIn$_5$ which for low concentrations first was shown to lead to the coexistence of antiferromagnetism with SC and to a complete suppression of SC at higher concentrations. At the same time, the lattice constant of YbCoIn$_5$ indicates that Yb enters this compound in a partially divalent configuration suggesting that Yb could also be suitable for doping holes into CeCoIn$_5$. In our substitution series we find that that the unit cell volume stays roughly constant up to an Yb concentration of about 40~\%, after which the cell volume begins to decrease gradually to the value of YbCoIn$_5$. At the same time we observe a gradual suppression of the transition temperature $T_c$ to zero at an Yb concentration of 60~\%. Interestingly, the shape of $H$-$T$-phase diagram remains the same when the axis is scaled with the respective $T_c$ and upper critical field $H_{c2}$, suggesting that the ratio between Pauli $H_p$ and the orbital critical field $H_{c20}$ remains constant.