Distinct oxygen hole doping in different layers of $\rm Sr_{2}CuO_{4-\delta}-La_{2}CuO_4$ superlattices

TL;DR

This study uses resonant soft X-ray scattering to reveal layer-specific hole doping behaviors in Sr2CuO4−δ-La2CuO4 superlattices, showing distinct oxygen hole states on apical oxygens in different layers.

Contribution

It demonstrates layer-resolved doping differences and identifies apical oxygen as the site of a distinct hole state in superlattices, advancing understanding of layered cuprate heterostructures.

Findings

Different hole states are maximized in separate layers.

Hole occupation involves apical oxygen atoms polarized in the plane.

Surface reflectivity and interference effects help distinguish layer-specific scatterers.

Abstract

X-ray absorption in $\rm Sr_{2}CuO_{4-\delta}-La_{2}CuO_4$ (SCO-LCO) superlattices shows a variable occupation with doping of a hole state different from holes doped for $x \lesssim x_{optimal}$ in bulk $\rm La_{2-x}Sr_{x}CuO_4$ and suggests that this hole state is on apical oxygen atoms and polarized in the $a-b$ plane. Considering the surface reflectivity gives a good qualitative description of the line shapes of resonant soft X-ray scattering. The interference between superlattice and surface reflections was used to distinguish between scatterers in the SCO and the LCO layers, with the two hole states maximized in different layers of the superlattice.