Distinct oxygen hole doping in different layers of $\rm   Sr_{2}CuO_{4-\delta}-La_{2}CuO_4$ superlattices
  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. 
S. Smadici, J.C.T. Lee, P. Abbamonte, A. Rusydi, G. Logvenov, and I.   Bozovic
cond-mat.supr-con cond-mat.str-el