Oxygen superstructures throughout the phase diagram of $\bf (Y,Ca)Ba_2 Cu_3 O_{6+x}$

TL;DR

This study investigates short-range oxygen superstructures in (Y,Ca)Ba2Cu3O6+x across various doping levels using high-energy x-ray scattering, revealing a new superstructure linked to oxygen vacancy ordering.

Contribution

It identifies a novel four-unit-cell superstructure in (Y,Ca)Ba2Cu3O6+x and clarifies its origin as oxygen vacancy ordering, not electronic instabilities.

Findings

Discovered a new four-unit-cell superstructure at x~0.95

Superstructure attributed to oxygen vacancy ordering

No significant diffuse scattering in YBa2Cu4O8

Abstract

Short-range lattice superstructures have been studied with high-energy x-ray diffuse scattering in underdoped, optimally doped, and overdoped $\rm (Y,Ca)Ba_2 Cu_3 O_{6+x}$. A new four-unit-cell superstructure was observed in compounds with $x\sim 0.95$. Its temperature, doping, and material dependence was used to attribute its origin to short-range oxygen vacancy ordering, rather than electronic instabilities in the $\rm CuO_2$ layers. No significant diffuse scattering is observed in YBa$_2$Cu$_4$O$_{8}$. The oxygen superstructures must be taken into account when interpreting spectral anomalies in $\rm (Y,Ca)Ba_2 Cu_3 O_{6+x}$.