Abstract
We theoretically study three-dimensional topological semimetals (TSMs) with nodal lines protected by crystalline symmetries. Compared with TSMs with point nodes, e.g., Weyl semimetals and Dirac semimetals, where the conduction and the valence bands touch at discrete points, in these new TSMs the two bands cross at closed lines in the Brillouin zone. We propose two new classes of symmetry protected nodal lines in the absence and in the presence of spin-orbital coupling (SOC), respectively. In the former, we discuss nodal lines that are protected by the combination of inversion symmetry and time-reversal symmetry; yet unlike any previously studied nodal lines in the same symmetry class, each nodal line has a $Z_2$ monopole charge and can only be created (annihilated) in pairs. In the second class, with SOC, we show that a nonsymmorphic symmetry (screw axis) protects a four-band crossing nodal line in systems having both inversion and time-reversal symmetries.
Highlights
The study of topological semimetals has recently drawn much attention from both the theoretical and the experimental communities
We theoretically study three-dimensional topological semimetals (TSMs) with nodal lines protected by crystalline symmetries
With spin-orbital coupling (SOC), we show that a nonsymmorphic symmetry protects a four-band crossing nodal line in systems having both inversion and time-reversal symmetries
Summary
The study of topological semimetals has recently drawn much attention from both the theoretical and the experimental communities. We theoretically study three-dimensional topological semimetals (TSMs) with nodal lines protected by crystalline symmetries. We propose two new classes of symmetry protected nodal lines in the absence and in the presence of spin-orbital coupling (SOC), respectively.
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