Resonant inelastic x-ray scattering study of overdoped La[subscript 2-x]Sr[subscript x]CuO[subscript 4]

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S. Wakimoto, Young-June Kim, Hyunkyung Kim, H. Zhang, T. Gog, R.J. Birgeneau

Abstract:
Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge has been performed for heavily overdoped samples of La2-xSrxCuO4 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 (<= 3 eV) continuum excitation intensity has been studied utilizing the high-energy resolution of 0.13 eV (full width at half maximum). 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 (0 0) 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.