Compressibility of $CeMI{n}_5$ and $C{e}_{2}MI{n}_8$ (M = Rh, Ir and Co) Compounds

Abstract

The lattice parameters of the tetragonal compounds Ce$M$In${}_5$ and Ce${}_{2}M$In${}_8$($M=$Rh, Ir and Co) have been studied as a function of pressure up to 15 GPa using a diamond anvil cell under both hydrostatic and quasihydrostatic conditions at room temperature. The addition of $M$In${}_2$ layers to the parent CeIn${}_3$ compound is found to stiffen the lattice as the 2-layer systems (average of bulk modulus values $B_0$ is 70.4 GPa) have a larger $B_0$ than CeIn${}_3$ (67 GPa), while the 1-layer systems with the are even stiffer (average of $B_0$ is 81.4 GPa). Estimating the hybridization using parameters from tight binding calculations shows that the dominant hybridization is $fp$ in nature between the Ce and In atoms. The values of $V_{pf}$ at the pressure where the superconducting transition temperature $T_c$ reaches a maximum is the same for all Ce$M$In${}_5$ compounds. By plotting the maximum values of the superconducting transition temperature $T_c$ versus $c/a$ for the studied compounds and Pu-based superconductors, we find a universal $T_c$ versus $c/a$ behavior when these quantities are normalized appropriately. These results are consistent with magnetically mediated superconductivity.

Updated version resubmitted to Phys. Rev. B