Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hybrid-order topological insulators in a phononic crystal   Topological phases, including the conventional first-order and higher-order
topological insulators and semimetals, have emerged as a thriving topic in the
fields of condensed-matter physics and material science. Usually, a topological
insulator is characterized by a fixed order topological invariant and exhibits
associated bulk-boundary correspondence. Here, we realize a new type of
topological insulator in a bilayer phononic crystal, which hosts simultaneously
the first-order and second-order topologies, referred here as the hybrid-order
topological insulator. The one-dimensional gapless helical edge states, and
zero-dimensional corner states coexist in the same system. The new hybrid-order
topological phase may produce novel applications in topological acoustic
devices.

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The categories of this paper are: plasm-ph
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The categories of this paper are: solv-int
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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: quant-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: q-alg
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The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: physics
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom