Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological nodal line semimetals with and without spin-orbital coupling   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.

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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: econ
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-lat
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: adap-org
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The categories of this paper are: hep-ph
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The categories of this paper are: astro-ph