Antiferromagnetic metal-insulator transition of NiS_2-xSe_x: DFT+DMFT study

NiS_2-xSe_x is one of the archetypal and clean Mott material which exhibits metal-insulator transition (MIT) within long-range antiferromagnetic (AFM) order. Previous model studies for metal-insulator-transition inside the AFM dome employed magnetic frustration and was able to successfully describe the phase diagram including metal/insulator phases both with and without magnetic ordering, also describing the phase diagram of one of Mott materials, V₂O₃. However, NiS_2-xSe_x exhibited qualitative difference, representatively, the sign of the slope of T_MIT does change as the system entering the AFM dome. It provokes the question whether NiS_2-xSe_x can be a material realization of Mott-physics-induced metal-insulator transition with magnetic ordering, possibly showing a collapse of the Kondo screening which was not seen in the previous studies. In this work, using first-principles density functional theory and embedded dynamical mean-field theory calculation, we reproduced the magnetic metal-insulator transition phase diagram of NiS_2-xSe_x including both pressure- and temperature-induced consecutive metal-insulator and magnetic phase transition. Based on these results we will propose that the MIT of NiS_2-xSe_x within magnetic phase is not itinerant-type gap opening, but rather due to Mott physics. We will also discuss the peculiar dual nature of the Ni d local moments to realize this phase transition.