Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of emergent Dirac physics at the surfaces of acoustic
  higher-order topological insulators   Using three-dimensional (3D) sonic crystals as acoustic higher-order
topological insulators (HOTIs), we discover two-dimensional (2D) surface states
described by spin-1 Dirac equations at the interfaces between the two sonic
crystals with distinct topology but the same crystalline symmetry. We find that
the Dirac mass can be tuned by the geometry of the two sonic crystals. The sign
reversal of the Dirac mass reveals a surface topological transition where the
surface states exhibit zero refractive index behavior. When the surface states
are gapped, one-dimensional (1D) hinge states emerge due to the topology of the
gapped surface states. We confirm experimentally the zero refractive index
behavior and the emergent topological hinge states. Our study reveals a
multidimensional Wannier orbital control that leads to extraordinary properties
of surface states and unveils an interesting topological mechanism for the
control of surface waves.

11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
13
The categories of this paper are: quant-ph