Abstract
Based on first principle calculations, we show that a family of nonmagnetic materials including TaAs, TaP, NbAs and NbP are Weyl semimetal (WSM) without inversion center. We find twelve pairs of Weyl points in the whole Brillouin zone (BZ) for each of them. In the absence of spin-orbit coupling (SOC), band inversions in mirror invariant planes lead to gapless nodal rings in the energy-momentum dispersion. The strong SOC in these materials then opens full gaps in the mirror planes, generating nonzero mirror Chern numbers and Weyl points off the mirror planes. The resulting surface state Fermi arc structures on both (001) and (100) surfaces are also obtained and show interesting shapes, pointing to fascinating playgrounds for future experimental studies.
Highlights
Most topological invariants in condensed-matter noninteracting phases are defined on closed manifolds in momentum space
Based on first-principle calculations, we show that a family of nonmagnetic materials including TaAs, TaP, NbAs, and NbP are Weyl semimetals (WSM) without inversion centers
Further symmetry analysis shows that the two bands that cross along the Z to N line belong to opposite mirror eigenvalues, and the crossing between them is protected by mirror symmetry
Summary
Most topological invariants in condensed-matter noninteracting phases are defined on closed manifolds in momentum space. Topological metals can be defined by Chern numbers of the singleparticle wave functions at the Fermi surface energies [3,4,5] Such nonzero FS Chern numbers appear when the FS encloses a band-crossing point—the Weyl point—which can be viewed as a singular point of Berry curvature or “magnetic monopole” in momentum space [6,7,8,9]. Another proposal involves a finetuned multilayer structure of normal insulators and magnetically doped topological insulators [18] These proposed WSM systems involve magnetic materials, where the spin degeneracy of the bands is removed by breaking timereversal symmetry.
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