Tuning quantum paramagnetism and d-wave superconductivity in single-layer iron chalcogenides by chemical pressure

TL;DR

This study demonstrates how chemical pressure via sulfur substitution in single-layer FeSe/SrTiO3 tunes its magnetic and superconducting properties, revealing a transition from paramagnetism to d-wave superconductivity with nodal gaps.

Contribution

It introduces a method to control quantum magnetism and superconductivity in iron chalcogenides through chemical pressure, linking electronic structure changes to superconducting gap symmetry.

Findings

Electronic bands resemble antiferromagnetic order.

Superconducting gap evolves from U-shaped to V-shaped.

Nodes appear when gap size is smaller than spin-orbit coupling.

Abstract

By substituting S into single-layer FeSe/SrTiO3, chemical pressure is applied to tune its paramagnetic state that is modeled as an incoherent superposition of spin-spiral states. The resulting electronic bands resemble an ordered checkerboard antiferromagnetic structure, consistent with angle-resolved photoemission spectroscopy measurements. Scanning tunneling spectroscopy reveals a gap evolving from U-shaped for FeSe to V-shaped for FeS with decreasing size, attributed to a d-wave superconducting state for which nodes emerge once the gap size is smaller than the effective spin-orbit coupling.