Friedel-like Oscillations from Interstitial Iron in Superconducting Fe1+yTe0.62Se0.38

TL;DR

This study reveals that interstitial iron in superconducting FeTeSe induces magnetic Friedel-like oscillations, affecting local magnetic order and potentially influencing superconductivity.

Contribution

It demonstrates the magnetic Friedel-like oscillations caused by interstitial Fe and models their origin using a semi-metallic five-band framework.

Findings

Interstitial Fe induces magnetic Friedel-like oscillations.

Oscillations involve over 50 neighboring Fe sites.

The semi-metallic model explains the diffraction pattern.

Abstract

Using polarized and unpolarized neutron scattering we show that interstitial Fe in superconducting Fe_{1+y}Te_{1-x}Se_x induces a magnetic Friedel-like oscillation that diffracts at Q_(in-plane)=(1/2,0) and involves >50 neighboring Fe sites. The interstitial >2 mu_B moment is surrounded by compensating ferromagnetic four spin clusters that may seed double stripe ordering in Fe_{1+y}Te. A semi-metallic 5-band model with (1/2,1/2) Fermi surface nesting and four fold symmetric super-exchange between interstitial Fe and two in-plane nearest neighbors largely accounts for the observed diffraction.