Nominal doping and partition of doped holes between planar and apical orbitals in La2-xSrxCuO4

TL;DR

This study investigates how holes are distributed between different orbitals in La2-xSrxCuO4, confirming most doping occurs in planar orbitals but with some charge in apical orbitals, refining understanding of doping mechanisms.

Contribution

It provides a quantitative analysis of hole distribution between planar and apical orbitals in La2-xSrxCuO4, challenging previous hypotheses and offering a calibration curve for doping levels.

Findings

Doped holes mainly occupy planar orbitals.

A small fraction of holes enter apical orbitals.

Quantitative doping relation p = x (1.00(1) - 0.45(7) x) is established.

Abstract

By considering both the average structural parameters obtained from Rietveld refinement of neutron powder diffraction data, and the local structural parameters obtained from the atomic pair distribution function, we have tested the recent hypothesis of Perry et al [Perry et al., Phys. Rev. B v.65, 144501 (2002)] that doping in La2-xSrxCuO4 system occurs as localized defects of predominantly Cud3z^2-r^2--Opz character associated with the Sr dopants accompanied by a local destruction of the Jahn-Teller distortion. While the structural parameters behave qualitatively according to the prediction of this model, a quantitative analysis indicates that doped holes predominantly appear in the planar Cudx^2-y^2--Opx,y band as is normally assumed. However, a small amount of the doped charge does enter the Cud3z^2-r^2--Opz orbitals and this should be taken into account when theoretical phase diagrams are compared to experiment. We present a calibration curve, p = x (1.00(1) - 0.45(7) x), for the planarcharge doping, p, vs strontium content, x, for the La2-xSrxCuO4 system.