Boron local density of states of Y(Rh/sub 1-x/Ru/sub x/)4B4 superconductors

Local electronic density of states (DOS) at the boron site for Y(Rh/sub 1-x/Ru/sub x/)4B4 superconductors, with x = 0.15, 0.50, and 0.85, have been characterized by means of B KVV Auger line-shape analyses, with supporting data from x-ray- and ultraviolet-photoemission experiments and electron-energy-loss experiments. The motivation was to test Johnston's model, in which the unusually precipitous drop of the superconducting transition temperature for x> or approx. =0.5 is attributed to an abrupt charge transfer to the boron site. Comparisons of the experimental Auger line shapes are made to those we have generated from band-structure calculations by Jarlborg et al. for the related compound YRh4B4. The Auger data reveal a continuous evolution of the B local DOS with x, which does not support the Johnston model. The analyses indicate that there is a continuous modification of the hybridization of the B p-like and the transition-metal d-like electronic states with x. We suggest that these changes in the pd hybridization may be related to a previously reported lattice distortion for this system, and that these effects directly influence the electron-phonon interaction strength