Dirac and Weyl Semimetals in Sn_1−xIn_xTe

Abstract

The recent realization of Weyl fermions in materials [1-10] has received a great deal of attention due to their connection with particle physics, in addition to the promise for technological applications. [11-13] These fermions belong to the topological semimetal class of materials, with accidental degeneracy states around the Fermi level that are protected by topology and symmetry. The protected Weyl fermions present a nonvanishing Chern number around each chiral node. The degenerated chiral points are located in the bulk band structure, connected with surface Fermi arcs. [3-9] There are some conditions to realize Weyl semimetal (WSM) in an inverted bandgap 3D material: the valence and conduction bands must touch each other at the some point of the bulk Brillouin zone (BZ), and a lack of either time reversal or inversion symmetry must occur. With that, the crossing point is symmetry-preserved and pairs of Weyl nodes with opposite chirality are realized. If time reversal and inversion symmetry are preserved in an inverted gap system, the Weyl nodes annihilate, resulting in a Dirac semimetal (DSM) phase. [14-21] In this case the net Chern number is zero; the Dirac crossing is fourfold degenerated and it is not topologically protected, [10] but crystal symmetry can protect the degeneracies if the semimetal character comes from a topological insulator bulk gap closure. Recently, it has been predicted that distinct semimetal topological phases can be obtained by defect engineering with impurities [22] in topological crystalline insulator (TCI) materials. This novel topological class has attracted attention lately [23-29] because their topological sates are protected by crystal symmetry, distinct from Z 2 topological insulators that are protected by time reversal symmetry. Pressure also has been shown to induce topological semimetal phase in TCIs. [30]