Electronic properties of Sc5M4Si10 (M = Co, Rh, Ir) probed by NMR and first-principles calculations

We report a systematic study of Sc-45 NMR measurements on the Sc5Co4Si10-type silicides Sc5M4Si10(M = Co, Rh, Ir). From the central transition line shapes, three nonequivalent Sc sites have been identified. We thus measured the Knight shift and spin-lattice relaxation time (T-1) for each of the three crystallographic sites. Results of experimental Knight shift and T-1 together with theoretical band structure calculations provide evidence that orbital electrons are responsible for the observed shifts as well as the relaxation rates. In addition, we found no correlation between the Fermi-level density of states and the superconducting transition temperature of the studied materials. Further analyses clearly indicate that the effect of electron-phonon coupling plays a significant role for the superconductivity of Sc5M4Si10, and these materials should be classified as moderate-coupling superconductors.