Metal-insulator transition in NiS$_{2-x}$Se$_x$

TL;DR

This study combines theoretical and experimental methods to investigate the origins of the electronic gap and the metal-insulator transition in NiS2-xSex, highlighting the role of bonding-antibonding splitting in dimers.

Contribution

It provides a comprehensive analysis of the gap formation and transition mechanisms in NiS2-xSex using first-principles calculations and spectroscopic experiments, emphasizing the importance of dimer splitting.

Findings

Bonding-antibonding splitting controls the charge gap.

Pressure and Se doping influence the metal-insulator transition.

Theoretical and experimental results are consistent in explaining the transition.

Abstract

The origin of the gap in NiS2 as well as the pressure- and doping-induced metal-insulator transition in the NiS2-xSex solid solutions are investigated both theoretically using the first-principles band structures combined with the dynamical mean-field approximation for the electronic correlations and experimentally by means of infrared and x-ray absorption spectroscopies. The bonding-antibonding splitting in the S-S (Se-Se) dimer is identified as the main parameter controlling the size of the charge gap. The implications for the metal-insulator transition driven by pressure and Se doping are discussed.