Suppression of orbital ordering by chemical pressure in FeSe1-xSx

TL;DR

This study uses high-resolution ARPES to examine how chemical pressure from sulfur substitution affects the electronic structure and orbital ordering in FeSe1-xSx, revealing suppression of structural transition and changes in orbital band splitting.

Contribution

It provides detailed insights into how isovalent S substitution suppresses orbital ordering and modifies the electronic structure in FeSe, advancing understanding of structural transitions in iron-based superconductors.

Findings

Suppression of structural transition temperature from 87K to 58K with S substitution.

Reduction in band splitting between dyz and dxz orbitals as S content increases.

Detection of the inner hole pocket below the Fermi level at x=0.12.

Abstract

We report a high-resolution angle-resolved photo-emission spectroscopy study of the evolution of the electronic structure of FeSe1-xSx single crystals. Isovalent S substitution onto the Se site constitutes a chemical pressure which subtly modifies the electronic structure of FeSe at high temperatures and induces a suppression of the tetragonal-symmetry-breaking structural transition temperature from 87K to 58K for x=0.15. With increasing S substitution, we find smaller splitting between bands with dyz and dxz orbital character and weaker anisotropic distortions of the low temperature Fermi surfaces. These effects evolve systematically as a function of both S substitution and temperature, providing strong evidence that an orbital ordering is the underlying order parameter of the structural transition in FeSe1-xSx. Finally, we detect the small inner hole pocket for x=0.12, which is pushed below the Fermi level in the orbitally-ordered low temperature Fermi surface of FeSe.