Effect of impurity substitution on band structure and mass renormalization of the correlated FeTe$_{0.5}$Se$_{0.5}$ superconductor

TL;DR

This study uses ARPES to investigate how Ni impurity substitution affects the electronic structure, band renormalization, and orbital sensitivity in FeTe$_{0.5}$Se$_{0.5}$ superconductor, revealing deviations from the rigid-band model.

Contribution

It provides detailed experimental insights into impurity effects on band structure and mass renormalization in Fe-based superconductors, highlighting orbital-dependent sensitivity.

Findings

Hole pockets decrease in size with doping

Effective mass of hole pockets is reduced

Changes are inconsistent with rigid-band model

Abstract

Using angle-resolved photoemission spectroscopy (ARPES), we studied the effect of the impurity potential on the electronic structure of FeTe$_{0.5}$Se$_{0.5}$ superconductor by substituting 10\% of Ni for Fe which leads to an electron doping of the system. We could resolve three hole pockets near the zone center and an electron pocket near the zone corner in the case of FeTe$_{0.5}$Se$_{0.5}$, whereas only two hole pockets near the zone center and an electron pocket near the zone corner are resolved in the case of Fe$_{0.9}$Ni$_{0.1}$Te$_{0.5}$Se$_{0.5}$, suggesting that the hole pocket having predominantly the $xy$ orbital character is very sensitive to the impurity scattering. Upon electron doping, the size of the hole pockets decrease and the size of the electron pockets increase as compared to the host compound. However, the observed changes in the size of the electron and hole pockets are not consistent with the rigid-band model. Moreover, the effective mass of the hole pockets is reduced near the zone center and of the electron pockets is increased near the zone corner in the doped Fe$_{0.9}$Ni$_{0.1}$Te$_{0.5}$Se$_{0.5}$ as compared to FeTe$_{0.5}$Se$_{0.5}$. We refer these observations to the changes of the spectral function due to the effect of the impurity potential of the dopants.