Prediction of ferromagnetic Weyl semimetal and antiferromagnetic topological insulator phases in MnHg₂Te₃

Based on first-principles band-structure calculations, we predict that FM MnHg2Te3 is a Weyl semimetal candidate. When the direction of spin polarization is toward the c-axis, there are six Weyl points in the whole Brillouin zone. With spin orientation along the a-axis, there exist eight Weyl points. For AFM MnHg2Te3, when the spin direction is along the c-axis, the band structure is fully gapped. The calculation of the Z2 number confirms that AFM-c MnHg2Te3 is a 3D AFM topological insulator. Adjusting the spin direction from the c-axis to the a-axis only changes the bandgap without affecting the topological properties of this system. The gapless surface-state on the (100) surface is also obtained, the results of which correspond with the properties of the AFM topological insulator.