Polarized Neutron Spectroscopy of Dynamical Magnetism in Parent and Superconducting Fe(Te,Se)*

Inelastic neutron scattering presented perhaps the first experimental indication of the orbital-selective electron localization in the Fe chalcogenides [1]. The follow-up study [2] established the concomitant ferro-orbital order, leading to the "bicollinear" antiferromagnetism, a metallic state, and a loss of magnetic susceptibility[1,2]. Here, we present polarized inelastic neutron surveys of the temperature-dependent magnetic dynamics in both Fe_1+yTe, and the optimally doped superconductor, FeTe_0.55Se_0.45. We observe that the local dynamical correlations in the superconducting sample in the energy range of the spin resonance, at high temperature become similar to those found in the under-doped samples [1], and which are also observed in the optimally doped samples at higher energy. Our results reveal unusual, energy- and temperature-dependent orbital composition of dynamical magnetism in these materials.
[1] I. A. Zaliznyak, et. al., Phys. Rev. Lett. 107, 216403 (2011).
[2] D. Fobes, et. al., Phys. Rev. Lett. 112, 187202 (2014).
[3] I. Zaliznyak, et. al., Proc Natl Acad Sci USA, 112(33), 10316-10320 (2015).