Revealing the Role of the Tetragonal Distortion in the Metal-Insulator Transition of Co- and Fe-Doped NiS

Although the NiS exhibits the most widely adjustable metal-to-insulator (MIT) properties among the chalcogenides, the mechanisms, with respect to the regulations in their critical temperatures (T (MIT)), are yet unclear. Herein, we demonstrate the overlooked role associated with the structurally tetragonal distortion in elevating the T (MIT) of NiS; this is in distinct contrast to the previously expected hybridization and bandwidth regulations that usually reduces T (MIT). Compared to the perspective of structure distortions, the orbital hybridization and band regulation of NiS are similar to 19 times more effective adjustment in T (MIT). As a result, the respective abruptions in both the electrical and thermal resistive switches across the T (MIT) of NiS can be better preserved in the low-temperature range (<273 K), shedding light on their optimum usage at cryogenic temperatures.