Orbital superconductivity, defects and pinned nematic fluctuations in the doped iron chalcogenide FeSe_0.45Te_0.55.

In this talk I will demonstrate that the differential conductance dI/dV, measured via spectroscopic imaging scanning tunneling microscopy in the doped iron chalcogenide FeSe_0.45Te_0.55, posseses a series of characteristic features that allow one to extract the orbital structure of the superconducting gaps. This yields nearly isotropic superconducting gaps on the two hole-like Fermi surfaces, and a strongly anisotropic gap on the electron-like Fermi surface. Moreover, I will show that the pinning of nematic fluctuations by defects can five rise to a dumbbell-like spatial structure of the induced impurity bound states, and explains the related C₂ symmetry in the Fourier transformed differential conductance.