Abstract
Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the next frontier of condensed matter and materials science. Although the first inversion breaking Weyl semimetal was recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal breaking Weyl and nodal line semimetals, remain elusive. They are predicted to exhibit exotic properties distinct from the inversion breaking TSMs including TaAs. In this paper, we identify the magnetic topological semimetal states in the ferromagnetic half-metal compounds Co2TiX (X = Si, Ge, or Sn) with Curie temperatures higher than 350 K. Our first-principles band structure calculations show that, in the absence of spin-orbit coupling, Co2TiX features three topological nodal lines. The inclusion of spin-orbit coupling gives rise to Weyl nodes, whose momentum space locations can be controlled as a function of the magnetization direction. Our results not only open the door for the experimental realization of topological semimetal states in magnetic materials at room temperature, but also suggest potential applications such as unusual anomalous Hall effect in engineered monolayers of the Co2TiX compounds at high temperature.
Highlights
Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the frontier of condensed matter and materials science
Topological semimetals (TSM) are electronic strong spin-orbit metals/semimetals whose Fermi surfaces arise from crossings between conduction and valence bands, which cannot be avoided due to nontrivial topology[1,2,3]
Such new states of topological matter have recently attracted worldwide interest because they may realize particles that remain elusive in high energy physics, exhibit quantum anomalies, host new topological surface states such as the Fermi arc and the drumhead surface states, and show exotic transport and spectroscopic behaviors arising from the novel bulk and surface topological band structures[4,5,6,7,8,9,10,11,12,13,14,15,16]
Summary
Electronic structures were calculated within the density functional theory (DFT)[45] framework with the projector augmented wave (PAW) method, using the VASP46,47. The bulk band structures, the experimental lattice constants a = 5.830 Å, a = 5.997 Å and a = 5.770 Å for Co2TiGe, Co2TiSn and Co2TiSi were respectively used. The spin-orbit coupling was employed in the electronic structure calculations as implemented in the VASP. P and d orbitals for Co and Ti, and s and p orbitals for the X (Ge, Si, or Sn) atom to construct the Wannier function[49]. The surface states of a semi-infinite slab were calculated using the iterative Green’s function method from the Wannier function based tight-binding model
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