Orbital superconductivity, defects and pinned nematic fluctuations in the doped iron chalcogenide FeSe$_{0.45}$Te$_{0.55}$

TL;DR

This study uses spectroscopic imaging STM to analyze the orbital structure of superconducting gaps and the effects of defects on nematic fluctuations in doped FeSeTe, revealing isotropic and anisotropic gaps and defect-induced impurity states.

Contribution

It provides detailed orbital gap structure and defect effects in FeSe$_{0.45}$Te$_{0.55}$, advancing understanding of superconductivity and nematic fluctuations in this material.

Findings

Nearly isotropic gaps on hole-like Fermi surfaces

Strongly anisotropic gap on electron-like Fermi surface

Defect pinning induces dumbbell-like impurity states and $C_2$ symmetry

Abstract

We demonstrate that the differential conductance, $dI/dV$, measured via spectroscopic imaging scanning tunneling microscopy in the doped iron chalcogenide FeSe$_{0.45}$Te$_{0.55}$, possesses 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, we show that the pinning of nematic fluctuations by defects can give rise to a dumbbell-like spatial structure of the induced impurity bound states, and explains the related $C_2$-symmetry in the Fourier transformed differential conductance.