Lack of coupling between superconductivity and orthorhombic distortion in stoichiometric single-crystalline FeSe

TL;DR

This study reveals that in FeSe single crystals, superconductivity does not suppress orthorhombic distortion but instead couples strongly to the in-plane area, indicating a different mechanism from other Fe-based superconductors.

Contribution

The paper demonstrates that superconductivity in FeSe is decoupled from orthorhombic distortion and couples to in-plane area, challenging previous assumptions based on other Fe-based superconductors.

Findings

Superconductivity does not reduce orthorhombicity below Tc.

Superconductivity couples strongly to the in-plane area.

FeSe exhibits features different from typical Fe-based superconductors.

Abstract

The coupling between superconductivity and othorhombic distortion is studied in vapor-grown FeSe single crystals using high-resolution thermal-expansion measurements. In contrast to the Ba122-based (Ba122) superconductors, we find that superconductivity does not reduce the orthorhombicity below Tc. Instead we find that superconductivity couples strongly to the in-plane area, which explains the large hydrostatic pressure effects. We discuss our results in light of the spinnematic scenario and argue that FeSe has many features quite different from the typical Fe-based superconductors.