Staging superstructures in high-$T_c$ Sr/O co-doped La$_{2-x}$Sr$_x$CuO$_{4+y}$

TL;DR

This study investigates the structural phases of high-$T_c$ superconductor La$_{2-x}$Sr$_x$CuO$_{4+y}$ with co-doping, revealing how staging superstructures depend on doping and temperature, and their relation to electronic phase separation.

Contribution

It provides new insights into how Sr and O co-doping influence staging superstructures and their phase transition behavior in high-$T_c$ superconductors.

Findings

Staging number increases with higher Sr doping.

Staging phases emerge abruptly as a second order phase transition.

Structural details do not directly affect electronic phase separation.

Abstract

We present high energy X-ray diffraction studies on the structural phases of an optimal high-$T_c$ superconductor La$_{2-x}$Sr$_x$CuO$_{4+y}$ tailored by co-hole-doping. This is specifically done by varying the content of two very different chemical species, Sr and O, respectively, in order to study the influence of each. A superstructure known as staging is observed in all samples, with the staging number $n$ increasing for higher Sr dopings $x$. We find that the staging phases emerge abruptly with temperature, and can be described as a second order phase transition with transition temperatures slightly depending on the Sr doping. The Sr appears to correlate the interstitial oxygen in a way that stabilises the reproducibility of the staging phase both in terms of staging period and volume fraction in a specific sample. The structural details as investigated in this letter appear to have no direct bearing on the electronic phase separation previously observed in the same samples. This provides new evidence that the electronic phase separation is determined by the overall hole concentration rather than specific Sr/O content and concommittant structural details.