Doping dependence of charge-transfer excitations in La2-xSrxCuO4 -: art. no. 094524

We report a resonant inelastic x-ray scattering (RIXS) study of the doping dependence of charge-transfer excitations in La2-xSrxCuO4. The momentum dependence of these charge excitations are studied over the whole Brillouin zone in underdoped (x=0.05) and optimally doped (x=0.17) samples, and compared with that of the undoped (x=0) sample. We observe a large change in the RIXS spectra between the x=0 and x=0.17 samples, while the RIXS spectra of the x=0.05 sample are similar to that of the x=0 sample. The most prominent effect of doped holes on the charge excitation spectra is the appearance of a continuum of intensity, which exhibits strong momentum dependence below 2 eV. For the x=0.17 sample, some of the spectral weight from the lowest-lying charge-transfer excitation of the undoped compound is transferred to the continuum intensity below the gap, in agreement with earlier optical studies. However, the higher-energy charge-transfer excitation carries significant spectral weight even for the x=0.17 sample. The doping dependence of the dispersion of this charge-transfer excitation is also discussed and compared with recent theoretical calculations.