First-principles study of the large-gap three-dimensional topological insulators M3Bi2 (M = Ca, Sr, Ba)

By means of first-principles calculations in combination with universal evolutionary structure search, we identified the crystalline structure of long-term argued M3Bi2 (M = Sr, Ca, and Ba), which crystallizes in a tubelike structure stacked by buckled graphenelike layers. The analyses of electronic structures revealed that this type of M3Bi2 is a native wide-gap three-dimensional topological insulator with the inverted band order induced mainly by crystal field effect. The spin-orbit coupling effect was found to open the band gap and further enhance the band inversion. Among them, Sr3Bi2 is most attractive due to its largest fundamental gap of about 0.3 eV and the directly inverted band gap of 0.81 eV at Gamma obtained within the framework of Green functionals (GW). Moreover, the computation also evidences that their tubelike structure is suitable for further treatment via magnetic dopants, which prefer to occupy 1b site. Interestingly, the ferromagnetic insulating state has been achieved for V- and Mn-doped cases. This may provide a further opportunity to observe the quantized anomalous Hall effect in its thin films.