Resonant inelastic X-ray scattering study of overdoped La${}_{2-x}$Sr${}_x$CuO${}_4$

Abstract

Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge has been performed for heavily overdoped samples of La${}_{2-x}$Sr${}_x$CuO${}_4$ with $x=0.25$ and 0.30. We have observed the charge transfer and molecular-orbital excitations which exhibit resonances at incident energies of $E_i=8.992$ and 8.998 keV, respectively. From a comparison with previous results on undoped and optimally-doped samples, we determine that the charge-transfer excitation energy increases monotonically as doping increases. In addition, the $E_i$-dependences of the RIXS spectral weight and absorption spectrum exhibit no clear peak at $E_i=8.998$ keV in contrast to results in the underdoped samples. The low-energy ($\le 3$ eV) continuum excitation intensity has been studied utilizing the high energy resolution of 0.13 eV (FWHM). A comparison of the RIXS profiles at $(\pi 0)$ and $(\pi \pi )$ indicates that the continuum intensity exists even at $(\pi \pi )$ in the overdoped samples, whereas it has been reported only at $(00)$ and $(\pi 0)$ for the $x=0.17$ sample. Furthermore, we also found an additional excitation on top of the continuum intensity at the $(\pi \pi )$ and $(\pi 0)$ positions.

7 pages, 7 figures