Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Symmetry-Enforced Nodal Chain Phonons   Topological phonons in crystalline materials have been attracting great
interest. However, most cases studied so far are direct generalizations of the
topological states from electronic systems. Here, we reveal a novel class of
topological phonons -- the symmetry-enforced nodal-chain phonons, which
manifest features unique for phononic systems. We show that with $D_{2d}$
little co-group at a non-time-reversal-invariant-momentum point, the phononic
nodal chain is guaranteed to exist owing to the vector basis symmetry of
phonons, which is a unique character distinct from electronic and other
systems. Combined with the spinless character, this makes the proposed
nodal-chain phonons enforced by symmorphic crystal symmetries. We further
screen all 230 space groups, and find five candidate groups. Interestingly, the
nodal chains in these five groups exhibit two different patterns: for
tetragonal systems, they are one-dimensional along the fourfold axis; for cubic
systems, they form a three-dimensional network structure. Based on
first-principles calculations, we identify K$_{2}$O as a realistic material
hosting almost ideal nodal-chain phonons. We show that the effect of LO-TO
splitting, another unique feature for phonons, helps to expose the nodal-chain
phonons in K$_{2}$O in a large energy window. In addition, all the five
candidate groups have spacetime inversion symmetry, so the nodal chains also
feature a quantized $\pi$ Berry phase. This leads to drumhead surface phonon
modes that must exist on multiple surfaces of a sample.

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The categories of this paper are: q-fin
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The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: physics
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The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom