Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electrical Control of Second-Harmonic Generation in a WSe2 Monolayer
  Transistor   Nonlinear optical frequency conversion, in which optical fields interact with
a nonlinear medium to produce new field frequencies, is ubiquitous in modern
photonic systems. However, the nonlinear electric susceptibilities that give
rise to such phenomena are often challenging to tune in a given material, and
so far, dynamical control of optical nonlinearities remains confined to
research labs as a spectroscopic tool. Here, we report a mechanism to
electrically control second-order optical nonlinearities in monolayer WSe2, an
atomically thin semiconductor. We show that the intensity of second-harmonic
generation at the A-exciton resonance is tunable by over an order of magnitude
at low temperature and nearly a factor of 4 at room temperature through
electrostatic doping in a field-effect transistor. Such tunability arises from
the strong exciton charging effects in monolayer semiconductors, which allow
for exceptional control over the oscillator strengths at the exciton and trion
resonances. The exciton-enhanced second-harmonic generation is
counter-circularly polarized to the excitation laser, arising from the
combination of the two-photon and one-photon valley selection rules that have
opposite helicity in the monolayer. Our study paves the way towards a new
platform for chip-scale, electrically tunable nonlinear optical devices based
on two-dimensional semiconductors.

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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: physics
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-ph
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The categories of this paper are: econ
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The categories of this paper are: cs
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The categories of this paper are: hep-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat