Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Lifshitz transitions, type-II Dirac and Weyl fermions, event horizon and
  all that   The type-II Weyl and type-II Dirac points emerge in semimetals and also in
relativistic systems. In particular, the type-II Weyl fermions may emerge
behind the event horizon of black holes. In this case the horizon with
Painleve-Gullstrand metric serves as the surface of the Lifshitz transition.
This relativistic analogy allows us to simulate the black hole horizon and
Hawking radiation using the fermionic superfluid with supercritical velocity,
and the Dirac and Weyl semimetals with the interface separating the type-I and
type-II states. The difference between such type of the artificial event
horizon and that which arises in acoustic metric is discussed. At the Lifshitz
transition between type-I and type-II fermions the Dirac lines may also emerge,
which are supported by the combined action of topology and symmetry. The
type-II Weyl and Dirac points also emerge as the intermediate states of the
topological Lifshitz transitions. Different configurations of the Fermi
surfaces, involved in such Lifshitz transition, are discussed. In one case the
type-II Weyl point connects the Fermi pockets, and the Lifshitz transition
corresponds to the transfer of the Berry flux between the Fermi pockets. In the
other case the type-II Weyl point connects the outer and inner Fermi surfaces.
At the Lifshitz transition the Weyl point is released from both Fermi surfaces.
These examples reveal the complexity and universality of topological Lifshitz
transitions, which originate from the ubiquitous interplay of a variety of
topological characters of the momentum-space manifolds. For the interacting
electrons, the Lifshitz transitions may lead to the formation of the
dispersionless (flat) band with zero energy and singular density of states,
which opens the route to room-temperature superconductivity.

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The categories of this paper are: physics
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
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The categories of this paper are: astro-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
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The categories of this paper are: econ
24
The categories of this paper are: dg-ga
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The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas