Temperature dependent As K-edge EXAFS studies of LaFe1-xCoxAsO (x = 0.0 and 0.11) single crystals

TL;DR

This study uses temperature-dependent polarized As K-edge EXAFS to reveal bond anomalies in LaFe1-xCoxAsO single crystals, identifying structural transitions and anomalies linked to superconductivity and magnetic properties.

Contribution

It introduces a polarized EXAFS approach that detects bond anomalies associated with phase transitions and superconductivity in LaFe1-xCoxAsO, improving upon previous unpolarized methods.

Findings

Detected Fe-As bond anomaly at 150K during tetragonal-orthorhombic transition.

Identified a broad anomaly around 60K in doped samples linked to superconductivity.

Correlated bond oscillations with resistivity, magnetic susceptibility, and thermal expansion.

Abstract

We report the experimental results of temperature dependent polarized As K-edge extended x-ray absorption fine structure (EXAFS) of LaFe1-xCoxAsO (x=0.0 and 0.11) single-crystals. By aligning the Fe-As bond direction in the direction of the x-ray beam polarization we have been able to identify an anomaly in the Fe-As bond correlations at the tetragonal to orthorhombic transition at 150K, while previous investigations with standard unpolarized EXAFS of undoped LaFeAsO powder samples were not able to detect any such anomaly. Using our approach we have been able to identify in the superconducting doped sample, LaFe0.89Co0.11AsO, a broad anomaly around 60 K. The low temperature anomaly has good correlations with the temperature dependence of several properties like resistivity, magnetic susceptibility, linear thermal expansion, etc indicating the emergence of the dynamical oscillations of the Fe - As pairs