Visualization and control of oxygen dopant ordering in a cuprate superconductor

Abstract

A proper amount of excess oxygen plays a significant role in hole-doped cuprate high-Tc superconductivity. Here, we directly resolve the interstitial oxygen atoms are located in the spacer La2O2+δ layers of La2CuO4+δ superconductors via integrated differential phase contrast (iDPC) technique. The distribution of dopant oxygen in La2CuO4+δ is observed to be related with local strain states. Induced large in-plane stress in the La2CuO4+δ film forms periodic alternating tensile and compressive strain in the La–O layers. The mobile interstitial oxygen dopants get self-organized, instead of randomly distributed, to form oxygen-depleted stripes separated by ordered oxygen interstitials. The influence of dopant oxygen on the local atomic lattice and electronic structure was further examined by density functional theory (DFT) calculations. The interplay between the interstitial oxygen dopants and the CuO6 octahedra not only accommodates the distortions of the local atomic arrangement but also alters the electronic states by transferring charge from the LaO planes to the CuO2 planes. Our results may also be applicable to other oxygen-doped cuprates with high-Tc superconductivity.