Doping dependence of charge-transfer excitations in La_{2-x}Sr_xCuO_4

TL;DR

This study uses resonant inelastic x-ray scattering to investigate how charge-transfer excitations in La_{2-x}Sr_xCuO_4 vary with doping levels, revealing significant spectral changes and momentum-dependent continua, advancing understanding of electronic structure in cuprates.

Contribution

First detailed RIXS analysis of doping-dependent charge-transfer excitations in La_{2-x}Sr_xCuO_4, highlighting spectral weight transfer and dispersion changes with doping.

Findings

Large spectral change between undoped and optimally doped samples.

Emergence of a momentum-dependent continuum below 2 eV with doping.

Retention of high-energy charge-transfer excitation even at high doping.

Abstract

We report a resonant inelastic x-ray scattering (RIXS) study of the doping dependence of charge-transfer excitations in $\rm La_{2-x}Sr_xCuO_4$. The mome ntum 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 sample, 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 a 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.