Ab initio prediction of pressure-induced structural phase transition of superconducting FeSe

TL;DR

This study uses ab initio calculations to predict pressure-induced phase transitions in FeSe, revealing multiple structural changes and their effects on electronic properties and superconductivity.

Contribution

It provides the first detailed ab initio predictions of pressure-driven phase transitions in FeSe, including new transition pathways and their impact on electronic structure.

Findings

FeSe transitions to NiAs, MnP, and CsCl-type structures under pressure.

All phases of FeSe are metallic with varying ionic and covalent interactions.

High pressure may cause structural/magnetic instability affecting superconductivity.

Abstract

External pressure driven phase transitions of FeSe are predicted using \textit{ab initio} calculations. The calculations reveal that $\alpha$-FeSe takes transitions to NiAs-type, MnP-type, and CsCl-type FeSe. Transitions from NiAs-type to MnP-type and CsCl-type FeSe is also predicted. MnP-type FeSe is also found to be able to transform to CsCl-type FeSe, which is easier from $\alpha$-FeSe than the transition to MnP-type FeSe, but comparable to the transition from NiAs-type FeSe. The calculated electronic structures show that all phases of FeSe are metallic, but the ionic interaction between Fe-Se bonds becomes stronger and the covalent interaction becomes weaker when the structural phase transition occurs from $\alpha$-FeSe to the other phases of FeSe. The experimentally observed decrease in $T_{c}$ of superconducting $\alpha$-FeSe at high pressure may be due to a structural/magnetic instability, which exists at high pressure. The results suggest us to increase the $T_{c}$ of $\alpha$-FeSe if such phase transitions are frustrated by suitable methods.