282 research outputs found
Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers
We report that the refractive index of transition metal dichacolgenide (TMDC)
monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in
the imaginary part and > 20% in the real part around exciton resonances using
CMOS-compatible electrical gating. This giant tunablility is rooted in the
dominance of excitonic effects in the refractive index of the monolayers and
the strong susceptibility of the excitons to the influence of injected charge
carriers. The tunability mainly results from the effects of injected charge
carriers to broaden the spectral width of excitonic interband transitions and
to facilitate the interconversion of neutral and charged excitons. The other
effects of the injected charge carriers, such as renormalizing bandgap and
changing exciton binding energy, only play negligible roles. We also
demonstrate that the atomically thin monolayers, when combined with photonic
structures, can enable the efficiencies of optical absorption (reflection)
tuned from 40% (60%) to 80% (20%) due to the giant tunability of refractive
index. This work may pave the way towards the development of field-effect
photonics in which the optical functionality can be controlled with CMOS
circuits
Optimal Scoring Rule Design
This paper introduces an optimization problem for proper scoring rule design.
Consider a principal who wants to collect an agent's prediction about an
unknown state. The agent can either report his prior prediction or access a
costly signal and report the posterior prediction. Given a collection of
possible distributions containing the agent's posterior prediction
distribution, the principal's objective is to design a bounded scoring rule to
maximize the agent's worst-case payoff increment between reporting his
posterior prediction and reporting his prior prediction.
We study two settings of such optimization for proper scoring rules: static
and asymptotic settings. In the static setting, where the agent can access one
signal, we propose an efficient algorithm to compute an optimal scoring rule
when the collection of distributions is finite. The agent can adaptively and
indefinitely refine his prediction in the asymptotic setting. We first consider
a sequence of collections of posterior distributions with vanishing covariance,
which emulates general estimators with large samples, and show the optimality
of the quadratic scoring rule. Then, when the agent's posterior distribution is
a Beta-Bernoulli process, we find that the log scoring rule is optimal. We also
prove the optimality of the log scoring rule over a smaller set of functions
for categorical distributions with Dirichlet priors
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