Resonant inelastic X-ray scattering study of overdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$

TL;DR

This study uses resonant inelastic X-ray scattering to investigate charge excitations in heavily overdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$, revealing doping-dependent changes in excitation energies and continuum intensities.

Contribution

It provides new insights into charge transfer and continuum excitations in overdoped cuprates, highlighting differences from underdoped and optimally doped samples.

Findings

Charge transfer excitation energy increases with doping.

No clear resonance peak at 8.998 keV in overdoped samples.

Continuum excitation exists at both $(b0)$ and $(bpi)$ in overdoped samples.

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 ($\leq 3$ 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 $(0 ~0)$ 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.