Electronic structure of Cu1-xNixRh2S4 and CuRh2Se4:: Band-structure calculations, x-ray photoemission, and fluorescence measurements

The electronic structure of spinel-type Cu1-xNixRh2S4 (x = 0.0, 0.1, 0.3, 0.5, 1.0) and CuRh2Se4 compounds has been studied by means of x-ray photoelectron (XPS) and fluorescent spectroscopy. Cu L-3, Ni L-3, S L-2,L-3, and Se M-2,M-3 x-ray emission spectra (XES) were measured near thresholds at Beamline 8.0 of the Lawrence Berkeley Laboratory's Advanced Light Source. XES measurements of the constituent atoms of these compounds, reduced to the same binding energy scale, are found to be in excellent agreement with XPS valence bands. The calculated XES spectra which include dipole matrix elements show that the partial density of states reproduce experimental spectra quite well. States near the Fermi level (E-F) have strong Rh d and S(Se) p character in all compounds. In NiRh2S4 the Ni 3d states contribute strongly at E-F, whereas in both Cu compounds the Cu 3d bands are only similar to 1 eV wide and centered similar to 2.5 eV below E-F, leaving very little 3d character at E-F. The density of stares at the Fermi level is less in NiRh2S4 than in CuRh2S4. This difference may contribute to the observed decrease, as a function of Ni concentration, in the superconducting transition temperature in Cu1-xNixRh2S4. The density of states of the ordered alloy Cu0.5Ni0.5Rh2S4 shows behavior that is more "split-band"-like than "rigid-band"-like.