Compressibility of CeMIn5 and Ce2MIn8 (M=Rh, Ir, and Co) compounds

The lattice parameters of the tetragonal compounds CeMIn5 and Ce2MIn8 (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 MIn2 layers to the parent CeIn3 compound is found to stiffen the lattice as the 2-layer systems (average of bulk modulus values B0 is 70.4 GPa) have a larger B0 than CeIn3 (67 GPa), while the 1-layer systems are even stiffer (average of B0 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 Vpf at the pressure where the superconducting transition temperature Tc reaches a maximum is the same for all CeMIn5 compounds. By plotting the maximum values of the superconducting transition temperature Tc versus c/a for the studied compounds and Pu-based superconductors, we find a universal Tc versus c/a behavior when these quantities are normalized appropriately. These results are consistent with magnetically mediated superconductivity