Doping-induced insulator-metal transition in the Lifshitz magnetic insulator NaOsO₃

By means of first principles schemes based on magnetically constrained density functional theory and on the band unfolding technique we study the effect of doping on the conducting behaviour of the Lifshitz magnetic insulator NaOsO₃. Electron doping is treated within a supercell approach by replacing sodium with magnesium at different concentrations (Mg_xNa_1-xOsO₃, x = 0.125, 0.25, 0.375, 0.5). Undoped NaOsO₃ is subjected to a temperaturedriven Lifshitz transition involving a continuous closing of the gap due to longitudinal and rotational spin fluctuations (Kim et al 2016 Phys. Rev. B 94 241113). Here we find that Mg doping suppresses the insulating state, gradually drives the system to a metallic state (via an intermediate bad metal phase) and the transition is accompanied by a progressive lowering of the Os magnetic moment. We inspected the role of longitudinal spin fluctuations by constraining the amplitude of the local Os moments and found that a robust metal state can be achieved below a critical moment. In analogy with the undoped case we conjecture that the decrease of the local moment can be controlled by temperature effects, in accordance with the theory of itinerant electron magnetism.