Lu L, Chabot-Couture G, Zhao X, Hancock J N, Kaneko N, Vajk O P, Yu G, Grenier S, Kim Y J, Casa D, Gog T, Greven M
Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
Phys Rev Lett. 2005 Nov 18;95(21):217003. doi: 10.1103/PhysRevLett.95.217003. Epub 2005 Nov 17.
We report a Cu -edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa(2)CuO(4+delta) at optimal doping (T(c)=96.5 K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly dispersive (<0.5 eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitation suggests the existence of a remnant charge-transfer gap deep in the superconducting phase. Quite generally, our results, which include additional data for the Mott insulator La(2)CuO(4), demonstrate the importance of exploring the incident photon-energy dependence of the RIXS cross section.
