The absence of a clear signature of the Zhang-Rice singlet in the photoelectron valence band spectra of copper germanate raised the question of the stability of this state, induced by one-electron removal processes, in large-gap systems. Following Okada and Kotani [Phys. Rev. B 63, 045103 (2001)], we have performed a study of the O $1s$ resonant x-ray emission for $\mathrm{Cu}{\mathrm{Ge}}_{1-x}{\mathrm{Si}}_x{\mathrm{O}}_3$ ($x=0$, 0.05, and 0.1) single crystals as a function of temperature and polarization. Our experiment shows that the temperature, angle, and polarization dependence of the inelastic scattering emission detected at a $3.6\mathrm{eV}$ Raman shift in the O $1s$ resonant x-ray spectra can be unambiguously identified with the Zhang-Rice-singlet excitation.

• Received 26 January 2007

DOI:https://doi.org/10.1103/PhysRevB.75.195106