Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental observation of a topological band gap opening in ultracold
  Fermi gases with two-dimensional spin-orbit coupling   The recent experimental realization of synthetic spin-orbit coupling (SOC)
opens a new avenue for exploring novel quantum states with ultracold atoms.
However, in experiments for generating two-dimensional SOC (e.g., Rashba type),
a perpendicular Zeeman field, which opens a band gap at the Dirac point and
induces many topological phenomena, is still lacking. Here we theoretically
propose and experimentally realize a simple scheme for generating two-dimension
SOC and a perpendicular Zeeman field simultaneously in ultracold Fermi gases by
tuning the polarization of three Raman lasers that couple three hyperfine
ground states of atoms. The resulting band gap opening at the Dirac point is
probed using spin injection radio-frequency spectroscopy. Our observation may
pave the way for exploring topological transport and topological superfluids
with exotic Majorana and Weyl fermion excitations in ultracold atoms.

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The categories of this paper are: math
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
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The categories of this paper are: hep-lat
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The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
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The categories of this paper are: eess
10
The categories of this paper are: q-bio
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The categories of this paper are: acc-phys
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The categories of this paper are: astro-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: stat
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The categories of this paper are: solv-int
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The categories of this paper are: cs