NMR Study in the Iron-Selenide Rb0.74Fe1.6Se2: Determination of the Superconducting Phase as Iron Vacancy-Free Rb0.3Fe2Se2

TL;DR

This study uses NMR techniques to identify a vacancy-free, superconducting phase in Rb0.74Fe1.6Se2, revealing its composition and electronic properties, and clarifying its relation to other Fe-based superconductors.

Contribution

It is the first to precisely identify the superconducting phase as iron vacancy-free Rb0.3Fe2Se2 using NMR spectroscopy.

Findings

Superconducting phase is vacancy-free Rb0.3Fe2Se2.

The SC phase has a narrow NMR line indicating absence of AF order.

The SC phase has approximately 0.15 electrons per Fe.

Abstract

77Se and 87Rb nuclear magnetic resonance (NMR) experiments on Rb0.74Fe1.6Se2 reveal clearly distinct spectra originating from a majority antiferromagnetic (AF) and a minority metallic-superconducting (SC) phase. The very narrow NMR line of the SC phase evidences the absence of Fe vacancies and any trace of AF order. The Rb content of the SC phase is deduced from intensity measurements identifying Rb0.3(1)Fe2Se2 as the actual composition of the SC fraction. The resulting estimate of 0:15 electrons/Fe brings this class of superconductors 245 family closer to the other Fe-based superconductor families.