Protonation induced high-Tc phases in iron-based superconductors evidenced by NMR and magnetization measurements

TL;DR

This study introduces a room-temperature ionic liquid gating method to protonate iron-based superconductors, inducing high-Tc phases and enabling direct NMR probing of superconductivity.

Contribution

It presents a novel protonation technique for tuning electronic states in Fe-based superconductors and demonstrates its effectiveness through NMR and magnetization measurements.

Findings

Protonation induces superconductivity in parent compounds.

Proton incorporation enhances Tc in certain superconductors.

NMR reveals high-Tc phases with no coherence peak.

Abstract

Chemical substitution during growth is a well-established method to manipulate electronic states of quantum materials, and leads to rich spectra of phase diagrams in cuprate and iron-based superconductors. Here we report a novel and generic strategy to achieve nonvolatile electron doping in series of (i.e. 11 and 122 structures) Fe-based superconductors by ionic liquid gating induced protonation at room temperature. Accumulation of protons in bulk compounds induces superconductivity in the parent compounds, and enhances the Tc largely in some superconducting ones. Furthermore, the existence of proton in the lattice enables the first proton nuclear magnetic resonance (NMR) study to probe directly superconductivity. Using FeS as a model system, our NMR study reveals an emergent high-Tc phase with no coherence peak which is hard to measure by NMR with other isotopes. This novel electric-field-induced proton evolution opens up an avenue for manipulation of competing electronic states (e.g. Mott insulators), and may provide an innovative way for a broad perspective of NMR measurements with greatly enhanced detecting resolution.