Formation of As-As Interlayer Bonding in the collapsed tetragonal phase of NaFe$_2$As$_2$ under pressure

TL;DR

This study combines experimental and computational methods to investigate pressure-induced structural changes in NaFe$_2$As$_2$, revealing the formation of As-As interlayer bonds and their relation to superconductivity.

Contribution

It provides new experimental evidence of As-As interlayer bonding formation in NaFe$_2$As$_2$ under pressure, confirming theoretical predictions.

Findings

Structural transition at 4 GPa from tetragonal to collapsed tetragonal phase.

Formation of As-As interlayer bonds under pressure.

Correlation between structural changes and superconductivity.

Abstract

NaFe$_2$As$_2$ is investigated experimentally using powder x-ray diffraction and Raman spectroscopy at pressures up to 23 GPa at room temperature and using ab-initio calculations. The results reveal a pressure-induced structural modification at 4 GPa from the starting tetragonal to a collapsed tetragonal phase. We determined the changes in interatomic distances under pressure that allowed us to connect the structural changes and superconductivity. The transition is related to the formation of interlayer As-As bonds at the expense of weakening of Fe-As bonds in agreement with recent theoretical predictions.