Electronic structure of YbGa1.15Si0.85 and YbGaxGe2-x probed by resonant x-ray emission and photoelectron spectroscopies.

We performed an x-ray spectroscopic study combining resonant x-ray emission spectroscopy (RXES) and photoelectron spectroscopy on the superconducting ternary silicide YbGa1.15Si0.85 and nonsuperconducting ternary germanide YbGaxGe2-x (x = 1.0 and 1.1). The Yb valence for all three compounds is found to be about 2.3. In YbGa1.15Si0.85 no temperature dependence of the Yb valence is observed in the RXES spectra in the temperature range of 7–300 K, while the valence shows a drastic increase under pressure from the Yb2+ state partially including itinerant electrons to the localized Yb3+ state. Differences are observed in the valence-band spectra of the photoelectron spectroscopy between YbGa1.15Si0.85 and YbGaxGe2-x, which may be attributed to the difference of crystal structure. We conclude that both the crystal structure of the planar GaSi layer in YbGa1.15Si0.85 and the resultant electronic structure may have a crucial role in the occurrence of superconductivity. [ABSTRACT FROM AUTHOR]