Gap opening and orbital modification of superconducting FeSe above the structural distortion

TL;DR

This study uses optical spectroscopy to reveal a high-temperature energy gap and orbital modifications in FeSe, indicating a link between electronic nematicity, charge order, and structural changes in iron-based superconductors.

Contribution

It demonstrates the presence of a gap and orbital modifications above structural distortion temperatures, suggesting a new understanding of precursor electronic orders in FeSe.

Findings

Detection of a ~36 meV energy gap above structural transition

Observation of spectral weight transfer in visible range

Evidence linking electronic nematicity to precursor order

Abstract

We utilize steady-state and transient optical spectroscopies to examine the responses of nonthermal quasiparticles with respect to orbital modifications in normal-state iron-chalcogenide superconductors. The dynamics shows the emergence of gap-like quasiparticles (associated to a ~36 meV energy gap) with a coincident transfer of the optical spectral weight in the visible range, at temperatures above the structural distortion. Our observations suggest that opening of the high-temperature gap and the lattice symmetry breaking are possibly driven by short-range orbital and/or charge orders, implicating a close correlation between electronic nematicity and precursor order in iron-based superconductors.