Study of the itinerant electron magnetism of Fe-based superconductors by the proximity effect

TL;DR

This study uses the proximity effect to investigate electron transport in Fe-based superconductors, revealing predominant itinerant electron magnetism and spin-polarized transport without residual magnetization in the normal state.

Contribution

It provides direct experimental evidence for itinerant electron magnetism in Fe-based superconductors using the proximity effect and Andreev reflection analysis.

Findings

Evidence of spin-polarized transport in FeSe and LaO(F)FeAs

Detection of spin-dependent Andreev reflection contributions

Hysteresis in FeSe conductivity at low magnetic fields

Abstract

We used the proximity effect as a tool to achieve an ideal (barrier - free) NS boundary for quantitative evaluation of transport phenomena that accompany converting dissipative current into supercurrent in NS systems with unconventional superconductors, single - crystal chalcogenide FeSe and granulated pnictide LaO(F)FeAs. Using features (limitations) of Andreev reflection in the NS systems with dispersion of the electron spin subbands, we revealed direct evidence for spin - polarized nature of transport and the absence of residual magnetization in iron - based superconductors in the normal state: In heterocontacts with single - crystal FeSe and granular LaO(F)FeAs, we detected a spin-dependent contribution to the efficiency of the Andreev reflection associated with the spin accumulation at the NS boundary, and a hysteresis of conductivity of FeSe in the ground state in low external magnetic fields. Based on our findings, we conclude that in iron-based superconductors, the itinerant electron magnetism is predominant, magnetism of iron atoms being localized.