9,439 research outputs found
Magneto-optical and Magneto-electric Effects of Topological Insulators in Quantizing Magnetic Fields
We develop a theory of the magneto-optical and magneto-electric properties of
a topological insulator thin film in the presence of a quantizing external
magnetic field. We find that low-frequency magneto-optical properties depend
only on the sum of top and bottom surface Dirac-cone filling factors
and , whereas the low-frequency
magneto-electric response depends only on the difference. The Faraday rotation
is quantized in integer multiples of the fine structure constant and the Kerr
effect exhibits a rotation. Strongly enhanced cyclotron-resonance
features appear at higher frequencies that are sensitive to the filling factors
of both surfaces. When the product of the bulk conductivity and the film
thickness in units is small compared to , magneto-optical
properties are only weakly dependent on accidental doping in the interior of
the film.Comment: 4 page
Giant Magneto-optical Kerr Effect and Universal Faraday Effect in Thin-film Topological Insulators
Topological insulators can exhibit strong magnetoelectric effects when their
time-reversal symmetry is broken. In this Letter we consider the
magneto-optical Kerr and Faraday effects of a topological insulator thin film
weakly exchange-coupled to a ferromagnet. We find that its Faraday rotation has
a universal value at low-frequencies, where is the vacuum fine structure
constant, and that it has a giant Kerr rotation .
These properties follow from a delicate interplay between thin-film cavity
confinement and the surface Hall conductivity of a topological insulator's
helical quasiparticles.Comment: 5 pages, 4 figure
Where does Volatility and Return Come From? The Case of Asian ETFs
We analyze return and volatility of Asian iShares traded in the U.S. The difference in trading schedules between the U.S. and Asia offers a unique market setting that allows us to distinguish various return and volatility sources. We find Asian ETFs have higher overnight volatility than daytime volatility, explained by public information released during each local market’s trading session. Local Asian markets also play an important role in determining each Asian ETF return. Nonetheless, returns for these funds are highly correlated with U.S. markets, indicative of the effects of investor sentiment and location of trade. Finally, returns in the U.S. market Granger-cause returns in all six Asian markets analyzed.International ETF; iShares; returns; variance; diversification
Convergence to Equilibrium in Wasserstein distance for damped Euler equations with interaction forces
We develop tools to construct Lyapunov functionals on the space of
probability measures in order to investigate the convergence to global
equilibrium of a damped Euler system under the influence of external and
interaction potential forces with respect to the 2-Wasserstein distance. We
also discuss the overdamped limit to a nonlocal equation used in the modelling
of granular media with respect to the 2-Wasserstein distance, and provide
rigorous proofs for particular examples in one spatial dimension
An analytical framework for a consensus-based global optimization method
In this paper we provide an analytical framework for investigating the
efficiency of a consensus-based model for tackling global optimization
problems. This work justifies the optimization algorithm in the mean-field
sense showing the convergence to the global minimizer for a large class of
functions. Theoretical results on consensus estimates are then illustrated by
numerical simulations where variants of the method including nonlinear
diffusion are introduced
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