Unconventional Multi-gap Superconductivity and Antiferromagnetic Spin Fluctuations in New Iron-arsenide LaFe2As2 in Heavily Electron-doped Regime

TL;DR

This study investigates the magnetic and superconducting properties of heavily electron-doped LaFe2As2 compounds, revealing unconventional multi-gap superconductivity linked to antiferromagnetic spin fluctuations, expanding understanding of iron-arsenide superconductors.

Contribution

It provides new insights into the relationship between antiferromagnetic spin fluctuations and multi-gap superconductivity in heavily electron-doped iron-arsenide compounds.

Findings

Antiferromagnetic order in parent compound at 130 K.

Enhanced AFM spin fluctuations in hole-doped and heavily electron-doped states.

Unconventional multi-gap superconductivity with weakened smaller gaps.

Abstract

We report 75As-NMR/NQR results on new iron-arsenide compounds (La0.5-xNa0.5+x)Fe2As2. The parent compound x=0 exhibits a stripe-type antiferromagnetic (AFM) order below T_N=130 K. The measurement of nuclear spin relaxation rate at hole-doped x=+0.3 and heavily electron-doped x=-0.5 revealed that the normal-state properties are dominated by AFM spin fluctuations (AFMSFs), which are more significant at x=+0.3 than at x=-0.5. Their superconducting (SC) phases are characterized by unconventional multi-gap SC state, where the smaller SC gaps are particularly weaken in common. The experimental results indicate the close relationship between the AFMSFs and the SC from the hole-doped state to heavily electron-doped state, which shed light on a unique SC phase emerged in the heavily electron-doped regime being formally equivalent to non-SC compound Ba(Fe0.5Co0.5)Fe2As2.