Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological semimetal phases in a family of monolayer X3YZ6 (X=Nb,Ta,
  Y=Si,Ge,Sn, Z=S,Se,Te) with abundant nodal lines and nodes   The electronic and topological properties of single-layer X3YZ6 (X=Nb,Ta,
Y=Si,Ge,Sn, Z=S,Se,Te) materials have been studied with the aid of first
principles calculations. This kind of materials belong to topological
semimetals (TMs) with abundant nodal lines and nodes. Considering their similar
properties, we focus on the analysis of Ta3SnTe6 and Ta3SiSe6. The present of
spin-orbit coupling (SOC) leads to the transition from type-I nodal lines to
Dirac points as well as the disappear of type-II Dirac points. The
three-dimensional (3D) band diagrams reproduce vividly the characteristics of
nodes and nodal lines. The appearance of the flat bands in (110) edge states
further confirm their nontrivial topological properties. We also explore the
relationship among different nodal lines (nodes), crystal symmetry and SOC. The
type-I nodal lines are protected by Mz and My symmetry in the absent of SOC.
Symmetry breaking leads to band splitting even in the presence of SOC. The
single-layer X3YZ6 can be used as candidates for two-dimensional (2D) TMs and
provide a platform for further study of interesting physical phenomena.

35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom