Band structure and topological phases of Pb1-x-ySnxMnyTe by ab initio calculations

A change in the composition of the Pb1-xSnxTe IV-VI semiconductor or in its lattice parameter can drive a transition from a topologically trivial to a topological crystalline insulator (TCI), crossing a region where the alloy is in the Weyl semimetal phase. Incorporation of the magnetic Mn ions induces strong perturbations of the electronic structure, which act on both orbital and spin variables. Our first principles calculations show that the presence of Mn shifts the TCI and the Weyl region towards higher Sn contents in Pb1-xSnxTe. When the Mn spin polarization is finite, the spin perturbation, like the orbital part, induces changes in band energies comparable to the bandgap, which widens the Weyl region. The effect opens the possibility of driving transitions between various topological phases of the system by a magnetic field or by spontaneous Mn magnetization. We also propose a new method to calculate topological indices for systems with a finite spin polarization defined based on the concept of the Chern number. These valid topological characteristics enable the identification of the three distinct topological phases of the Pb1-x-ySnxMnyTe alloy.

Automated summary

This study found that incorporating Mn into Pb1-xSnxTe alloy can shift the topological phases towards higher Sn contents, inducing perturbations in band energies and widening the Weyl region when the Mn spin polarization is finite. The research also proposed a new method to calculate topological indices for systems with finite spin polarization, based on the concept of the Chern number, to identify the distinct topological phases of the alloy.