Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Terahertz Kerr effect in a methylammonium lead bromide perovskite
  crystal   We have observed short-lived optical birefringence in a CH$_3$NH$_3$PbBr$_3$
single crystal induced by a powerful nearly single-cycle terahertz pulse. Apart
from the instantaneous contribution that follows the profile of the squared
pump electric field, the recorded anisotropy signal contains an exponential
component decaying in $\sim$ 350 fs, underdamped oscillations at the frequency
of $\sim$ 0.16 THz and an intermediate picosecond relaxation process with a
Gaussian tail. We associate these three non-trivial features with,
respectively, Kerr effect in the inorganic lattice, terahertz-induced transient
alignment of CH$_3$NH$_3^+$ cations, and their coherent rotation excited by the
terahertz pulse in a Raman process.

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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: math
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The categories of this paper are: q-alg
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The categories of this paper are: gr-qc
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The categories of this paper are: econ
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The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an