Determination of the local structure of Sr$_{2-x}$M$_x$IrO$_4$ (M = K, La) as a function of doping and temperature

TL;DR

This study investigates how doping and temperature affect the local atomic structure of Sr$_{2-x}$M$_x$IrO$_4$ using x-ray absorption, revealing stable Ir-O bonds but increased disorder in Ir-Sr correlations, suggesting nanoscale phase separation.

Contribution

It provides detailed insights into the local structural changes in Sr$_{2-x}$M$_x$IrO$_4$ with doping and temperature, highlighting the stability of Ir-O bonds and the increase in disorder with doping.

Findings

Ir-O bonds are strongly covalent and stable across Néel temperature.

No significant change in Ir-O bond dynamics with doping.

Increased static disorder in Ir-Sr correlations, especially with K doping.

Abstract

The local structure of correlated spin-orbit insulator Sr$_{2-x}$M$_x$IrO$_4$ (M = K, La) has been investigated by Ir L$_3$-edge extended x-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the N\'eel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating possibility of a nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed.