Topic
Brillouin zone
About: Brillouin zone is a research topic. Over the lifetime, 13849 publications have been published within this topic receiving 383077 citations.
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TL;DR: Temperature distribution in silica single-mode optical fibers, from -30 to +60 degrees C, is successfully measured by using Brillouin optical-fiber time-domain analysis.
Abstract: Temperature distribution in silica single-mode optical fibers, from -30 to +60 degrees C, is successfully measured by using Brillouin optical-fiber time-domain analysis. A temperature measurement accuracy of 3 degrees C with a spatial resolution of 100 m is attained over a fiber length of 1.2 km.
435 citations
TL;DR: The experimental findings are consistent with theoretical predictions of spin-polarized conduction and valence bands at the K point of the Brillouin zone, with the minimum gap occurring between bands of opposite electron spin.
Abstract: Transition metal dichalcogenides in the class MX_{2} (M=Mo, W; X=S, Se) have been identified as direct-gap semiconductors in the monolayer limit. Here, we examine light emission of monolayer WSe_{2} using temperature-dependent photoluminescence and time-resolved photoluminescence spectroscopy. We present experimental evidence for the existence of an optically forbidden dark state of the band-gap exciton that lies tens of meV below the optically bright state. The presence of the dark state is manifest in the strong quenching of light emission observed at reduced temperatures. The experimental findings are consistent with theoretical predictions of spin-polarized conduction and valence bands at the K point of the Brillouin zone, with the minimum gap occurring between bands of opposite electron spin.
421 citations
TL;DR: It is found that when ∈(r) is sharply peaked, photonic levels become almost degenerate throughout the Brillouin zone, corresponding to standing waves.
Abstract: The problems associated with the poor convergence of the Fourier transform of the hard-sphere dielectric function are discussed. A significant band gap between the eighth and ninth levels has been found for air spheres in fcc. We also consider a periodic array of Gaussian spheres, which converges well and allows a consistent and reliable determination of the general features of photonic bands. It is found that when \ensuremath{\epsilon}(r) is sharply peaked, photonic levels become almost degenerate throughout the Brillouin zone, corresponding to standing waves.
408 citations
TL;DR: SeeK-path as discussed by the authors is a free online service to compute and visualize the first Brillouin zone, labeled k -points and suggested band paths for any crystal structure, that made available at http://www.materialscloud.org/tools/seekpath/.
399 citations
TL;DR: In this paper, it was shown that the electronic structure of the low-energy bands in bilayer bilayer graphene consists of a series of semimetallic and topological phases, and that the gapped set of bands that exist around all magic angles have a nontrivial topology stabilized by a magnetic symmetry.
Abstract: We show that the electronic structure of the low-energy bands in the small angle-twisted bilayer graphene consists of a series of semimetallic and topological phases. In particular, we are able to prove, using an approximate low-energy particle-hole symmetry, that the gapped set of bands that exist around all magic angles have a nontrivial topology stabilized by a magnetic symmetry, provided band gaps appear at fillings of +/- 4 electrons per moire unit cell. The topological index is given as the winding number (a Z number) of the Wilson loop in the moire Brillouin zone. Furthermore, we also claim that, when the gapped bands are allowed to couple with higher-energy bands, the Z index collapses to a stable Z(2) index. The approximate, emergent particle-hole symmetry is essential to the topology of graphene: When strongly broken, nontopological phases can appear. Our Letter underpins topology as the crucial ingredient to the description of low-energy graphene. We provide a four-band short-range tight-binding model whose two lower bands have the same topology, symmetry, and flatness as those of the twisted bilayer graphene and which can be used as an effective low-energy model. We then perform large-scale (11000 atoms per unit cell, 40 days per k-point computing time) ab initio calculations of a series of small angles, from 3 degrees to 1 degrees, which show a more complex and somewhat different evolution of the symmetry of the low-energy bands than that of the theoretical moire model but which confirm the topological nature of the system.
399 citations