Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Symmetry protected topological phases characterized by isolated
  exceptional points   Exceptional point (EP) associated with eigenstates coalescence in
non-Hermitian systems has many exotic features. The EPs are generally sensitive
to system parameters, here we report symmetry protected isolated EPs in the
Brillouin zone (BZ) of a two-dimensional non-Hermitian bilayer square lattice;
protected by symmetry, the isolated EPs only move, merge, and split in the BZ.
The average values of Pauli matrices under the eigenstate of system Bloch
Hamiltonian define a real planar vector field, the topological defects of which
are isolated EPs associated with vortices. The winding number characterizes the
vortices and reveals the topological properties of the non- Hermitian system.
Different topological phases correspond to different EP configurations, which
are unchanged unless topological phase transition occurs accompanying with the
EPs merging or splitting.

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The categories of this paper are: q-bio
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: patt-sol
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The categories of this paper are: plasm-ph
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The categories of this paper are: physics
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The categories of this paper are: gr-qc
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The categories of this paper are: alg-geom
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The categories of this paper are: cs
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The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: mtrl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int