Experimental evidence of $T_c$ enhancement without the influence of spin fluctuations: NMR study on LaFeAsO_{1-x}H_x under a pressure of 3.0 GPa

TL;DR

This study demonstrates that in LaFeAsO_{1-x}H_x, T_c can be enhanced to nearly 50K under pressure without the involvement of spin fluctuations, suggesting alternative mechanisms like orbital degrees of freedom are responsible.

Contribution

It provides experimental evidence that T_c enhancement in this superconductor occurs independently of spin fluctuations, highlighting the role of other factors such as orbital effects.

Findings

T_c reaches 48K under 3.0 GPa pressure.

Spin fluctuations are not involved in T_c enhancement.

Orbital degrees of freedom may be key to high T_c.

Abstract

The electron-doped high-transition-temperature (T_c) iron-based pnictide superconductor LaFeAsO_{1-x}H_x has a unique phase diagram: superconducting (SC) double domes are sandwiched by antiferromagnetic phases at ambient pressure and they turn to a single dome with a maximum T_c that exceeds 45K at a pressure of 3.0 GPa. We studied whether spin fluctuations are involved in increasing T_c under a pressure of 3.0 GPa by using ^{75}As nuclear magnetic resonance (NMR) technique. The ^{75}As-NMR results for the powder samples show that T_c increases up to 48 K without the influence of spin fluctuations. The fact indicates that spin fluctuations are not involved in raising T_c, which implies that other factors, such as orbital degrees of freedom, may be important for achieving a high T_c of almost 50 K.