Effects of Disorder in FeSe : An Ab Initio Study

TL;DR

This study uses ab initio methods to analyze how various types of disorder, such as excess Fe, Se deficiency, and substitutions, affect the electronic structure and Fermi surface nesting in FeSe, highlighting the importance of accurate disorder modeling.

Contribution

It provides a detailed ab initio analysis of disorder effects in FeSe using the coherent-potential approximation, comparing it with other models.

Findings

Excess Fe significantly disorders Fe-derived bands.

Se-deficiency mainly affects Se-derived bands.

S and Te substitutions enhance Fermi surface nesting.

Abstract

Using the coherent-potential approximation, we have studied the effects of excess Fe, Se-deficiency, and substitutions of S, Te on Se sub-lattice and Co, Ni and Cu on Fe sub-lattice in FeSe. Our results show that (i) a small amount of excess Fe substantially disorders the Fe-derived bands while Se-deficiency affects mainly the Se-derived bands, (ii) the substitution of S or Te enhances the possibility of Fermi surface nesting, specially in FeSe$_{0.5}$Te$_{0.5}$, in spite of disordering the Se-derived bands, (iii) the electron doping through Co, Ni or Cu disorders the system and pushes down the Fe-derived bands, thereby destroying the possibility of Fermi surface nesting. A comparison of these results with the rigid-band, virtual-crystal and supercell approximations reveals the importance of describing disorder with the coherent-potential approximation.