Revisiting the phase diagram of T*-type La$_{1-x/2}$Eu$_{1-x/2}$Sr$_x$CuO$_4$ using Oxygen $K$-edge X-ray absorption spectroscopy

TL;DR

This study uses oxygen K-edge X-ray absorption spectroscopy to analyze hole density and phase diagram changes in T*-type La$_{1-x/2}$Eu$_{1-x/2}$Sr$_x$CuO$_4$, revealing annealing-induced hole delocalization and a revised phase diagram.

Contribution

It provides new insights into how annealing affects hole density and the phase diagram in T*-type cuprates, highlighting the role of delocalized holes.

Findings

Annealing causes a significant increase in hole density.

The increase in holes is not solely due to oxygen gain.

A revised phase diagram of LESCO was established.

Abstract

Oxygen $K$-edge X-ray absorption spectroscopy measurements were conducted on T*-type La$_{1-x/2}$Eu$_{1-x/2}$Sr$_x$CuO$_4$ (LESCO) to estimate the hole density ($n_{\rm h}$) and investigate the oxidation annealing effect on $n_{\rm h}$. A drastic increase in $n_{\rm h}$ due to annealing was found. The increase in $n_{\rm h}$ cannot be explained solely by the oxygen gain due to annealing, suggesting that delocalized holes are introduced into the CuO$_2$ plane. A phase diagram of LESCO was redrawn against $n_{\rm h}$.