Investigation of metal-insulator transition of NiS2 near critical transition criteria

Strongly correlated materials, such as NiS2, have been the subject of extensive study due to their remarkable and exotic physical properties. The dynamical mean-field theory (DMFT) framework has provided a reasonable approach to depicting strongly correlated materials by establishing a dynamical mean field, thereby having a crucial role in describing the intricate interactions among particles in the systems. Nichel disulfide (NiS2) represents a representative strongly correlated electron system exhibing a pressure/temperature-driven metal-insulator transition (MIT). This transition arises from the delicate balance between electronic bandwidth and Coulomb repulsion, making NiS2 an outstanding platform for understading correlation-induced phase evolution in transition-metal compounds. In this study, we systematically trace th temperature-dependent phase transition of NiS2 under a fixed pressure, and construct a continuous sequence of metallic and insulating self-energy seeds to rigorously determine the criterion for the metal-insulator transition. Under a pressure of 4.3GPa, a coexistence of metallic and insulating phases is observed between 75K and 85K. Moreover, a continuous moving of the alpha-spectral peak, consistent with former experimental observations, is detected through an intermediate phase exhibing sligh instability, suggesting a subtle transition pathway between the metal and insulating electronic states. The intermediate phase exhibits a transient behavior characterized by a outstanding enhancement of spectral coherence near the Fermi level compared to even the metallic phase. Despite the apprarent reduction in the Fermi surface, the electronic density at the Fermi level increases, indicating a nontrivial intermediate regime between coherent metallic and localized insulating states.