First-principles study of the large-gap three-dimensional topological insulatorsM3Bi2(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 ${M}_{3}{\mathrm{Bi}}_{2}$ ($M=\text{Sr}$, Ca, and Ba), which crystallizes in a tubelike structure stacked by buckled graphenelike layers. The analyses of electronic structures revealed that this type of ${M}_{3}{\mathrm{Bi}}_{2}$ 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, ${\mathrm{Sr}}_{3}{\mathrm{Bi}}_{2}$ 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 $\mathrm{\ensuremath{\Gamma}}$ 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.