Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Weyl and Dirac semimetals with Z_2 topological charge   We study the stability of gap-closing (Weyl or Dirac) points in the
three-dimensional Brillouin zone of semimetals using Clifford algebras and
their representation theory. We show that a pair of Weyl points with
$\mathbb{Z}_2$ topological charge are stable in a semimetal with time-reversal
and reflection symmetries when the square of the product of the two symmetry
transformations equals minus identity. We present toy models of $\mathbb{Z}_2$
Weyl semimetals which have surface modes forming helical Fermi arcs. We also
show that Dirac points with $\mathbb{Z}_2$ topological charge are stable in a
semimetal with time-reversal, inversion, and SU(2) spin rotation symmetries
when the square of the product of time-reversal and inversion equals plus
identity. Furthermore, we briefly discuss the topological stability of point
nodes in superconductors using Clifford algebras.

25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph