Abstract
We propose a kind of topological quantum state of semimetals in the quasi-one-dimensional (1D) crystal family (, Nb, or Ta; or Se) by using symmetry analysis and first-principles calculation. We find that in the valence and conduction bands are degenerate in the plane ( is the lattice constant along the axis) of the Brillouin zone (BZ). These nodal points form a node surface, and they are protected by a nonsymmorphic crystal symmetry consisting of a twofold rotation about the axis and a half-translation along the same axis. The band degeneracy in the node surface is lifted in by including strong spin-orbit coupling (SOC) of Ta. The node surface is reduced into 1D node lines along the high-symmetry paths and on the plane. These node lines are robust against SOC and guaranteed by the symmetries of the space group. These node-line states are entirely different from previous proposals which are based on the accidental band touchings. We also propose a useful material design for realizing topological node-surface and node-line semimetals.
- Received 2 January 2016
DOI:https://doi.org/10.1103/PhysRevB.93.085427
©2016 American Physical Society