Publication Type
Journal
Journal Name
Physical Review Letters
Publication Date
Page Number
107002
Volume
108
Issue
10
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 ${\bf Q}_{\perp}=(\frac{1}{2}0)$ 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 $(\frac{1}{2}\frac{1}{2})$ Fermi surface nesting and four fold symmetric super-exchange between interstitial Fe and two in-plane nearest neighbors largely accounts for the observed diffraction.
