The Structural Phase Transition in FeSe (Fe1+dSe)

TL;DR

This study reveals a structural phase transition in superconducting Fe1.01Se at 90 K from tetragonal to orthorhombic, with additional atomic displacements, and shows that magnetism is not responsible for this transition.

Contribution

It demonstrates a temperature-induced structural transition in FeSe and uncovers complex atomic modulations, distinguishing superconducting from non-superconducting phases.

Findings

Superconducting Fe1.01Se transitions at 90 K from tetragonal to orthorhombic.

Additional atomic displacements observed in the superconducting phase.

Magnetism is not the cause of the structural phase transition.

Abstract

In this letter we show that superconducting Fe1.01Se undergoes a structural transition at 90 K from a tetragonal to an orthorhombic phase but that non-superconducting Fe1.03Se does not. Further, high resolution electron microscopy study at low temperatures reveals an unexpected additional modulation of the crystal structure of the superconducting phase involving displacements of the Fe atoms, and that the non-superconducting material shows a distinct, complex nanometer-scale structural modulation. Finally, we show that magnetism is not the driving force for the phase transition in the superconducting phase.