18,228 research outputs found
Dirac fermion time-Floquet crystal: manipulating Dirac points
We demonstrate how to control the spectra and current flow of Dirac electrons
in both a graphene sheet and a topological insulator by applying either two
linearly polarized laser fields with frequencies and or a
monochromatic (one-frequency) laser field together with a spatially periodic
static potential(graphene/TI superlattice). Using the Floquet theory and the
resonance approximation, we show that a Dirac point in the electron spectrum
can be split into several Dirac points whose relative location in momentum
space can be efficiently manipulated by changing the characteristics of the
laser fields. In addition, the laser-field controlled Dirac fermion band
structure -- Dirac fermion time-Floquet crystal -- allows the manipulation of
the electron currents in graphene and topological insulators. Furthermore, the
generation of dc currents of desirable intensity in a chosen direction occurs
when applying the bi-harmonic laser field which can provide a straightforward
experimental test of the predicted phenomena.Comment: 9 pages, 7 figures, version that will appear in Phys. Rev.
New Economic Geography And Educational Attainment Levels In The European Union
In this paper a New Economic Geography model is used to analyse the distribution of educational attainment levels in the European Union. The results show that educational attainment levels decrease with distance to large consumer markets, proving that the theoretical predictions of the model are verified empirically
The Berry-Tabor conjecture for spin chains of Haldane-Shastry type
According to a long-standing conjecture of Berry and Tabor, the distribution
of the spacings between consecutive levels of a "generic'' integrable model
should follow Poisson's law. In contrast, the spacings distribution of chaotic
systems typically follows Wigner's law. An important exception to the
Berry-Tabor conjecture is the integrable spin chain with long-range
interactions introduced by Haldane and Shastry in 1988, whose spacings
distribution is neither Poissonian nor of Wigner's type. In this letter we
argue that the cumulative spacings distribution of this chain should follow the
"square root of a logarithm'' law recently proposed by us as a characteristic
feature of all spin chains of Haldane-Shastry type. We also show in detail that
the latter law is valid for the rational counterpart of the Haldane-Shastry
chain introduced by Polychronakos.Comment: LaTeX with revtex4, 6 pages, 6 figure
Determinantes de la elección de participación e ingresos en diferentes categorÃas de empleo en sectores rurales de Chile
Published by Asociación de Economistas Agrarios de Chilelabor market, multivariate probit, rural nonfarm employment, Community/Rural/Urban Development,
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