Coexistence of different electronic phases in the K0.8Fe1.6Se2 superconductor: a bulk-sensitive hard x-rays spectroscopy study

TL;DR

This study uses x-ray spectroscopy to reveal coexisting electronic phases in K0.8Fe1.6Se2, showing a link between a compressed low-spin phase and high-temperature superconductivity, highlighting its inhomogeneous, glassy nature.

Contribution

It provides the first detailed spectroscopic evidence of coexisting electronic phases and their relation to superconductivity in K0.8Fe1.6Se2.

Findings

Coexistence of high spin 3+Fe and intermediate spin 2+Fe phases.

High temperature annealing affects the spin state and superconductivity.

Superconductivity exhibits a glassy, inhomogeneous character.

Abstract

We have studied electronic and magnetic properties of the K0.8Fe1.6Se2 superconductor by x-ray absorption and emission spectroscopy. Detailed temperature dependent measurements alongwith a direct comparison with the binary FeSe system have revealed coexisting electronic phases: a majority phase with high spin 3+Fe state and a minority phase with intermediate spin 2+Fe state. The effect of high temperature annealing suggests that the compressed phase with lower spin 2+Fe state is directly related with the high Tc superconductivity in the title system. The results clearly underline glassy nature of superconductivity in the electronically inhomogeneous K0.8Fe1.6Se2, similar to the superconductivity in granular phases.