X-ray absorption spectroscopy (XAS) investigation of the electronic structure of superconducting FeSex single crystals

TL;DR

This study uses X-ray absorption spectroscopy to analyze the electronic structure and lattice distortions in FeSex single crystals, revealing hybridization effects, charge states, and structural changes related to Se deficiency.

Contribution

It provides new insights into the electronic states, charge distribution, and structural distortions in FeSex superconductors using XAS and XRD techniques.

Findings

Fe 4sp states and lattice distortion observed

Strong Fe 3d-Se 4p hybridization identified

Charge states of Fe and Se quantified and linked to structural changes

Abstract

X-ray absorption spectroscopy (XAS) Fe K-edge spectra of the FeSex (x=1-0.8) single crystals cleaved in situ in vacuum reveal characteristic Fe 4sp states, a lattice distortion and the Se K-edge spectra point to a strong Fe 3d-Se 4p hybridization giving rise to itinerant charge carriers. A formal charge of ~1.8+ for Fe and ~2.2- for Se were evaluated from these spectra in the FeSex (x=0.88). The charge balance between Fe and Se is assigned itinerant electrons located in the Fe-Se hybridization bond. As x decreases the 4p hole count increases and a crystal structure distortion is observed that in turn causes the Fe separation in the ab plane change from 4p orbital to varying (modulating) coordination. Powder x-ray diffraction (XRD) measurements also show a slight increase in lattice parameters as x decreases (increasing Se deficiency).