Brillouin zone

About: Brillouin zone is a research topic. Over the lifetime, 13849 publications have been published within this topic receiving 383077 citations.

Time-Resolved Investigations of Stimulated Brillouin Scattering in Transparent and Absorbing Media: Determination of Phonon Lifetimes

Abstract: Stimulated Brillouin scattering was studied both theoretically and experimentally. The evolution in time of the scattering process, its dependence on frequency, and the influence of optical absorption were analyzed. For quantitative investigations, the individual shapes of the laser and signal pulses were taken into account. Strong transient effects predicted by theory were confirmed experimentally. The amplification of Brillouin light was measured in a generator-amplifier system using single-mode giant laser pulses. Several liquids, glasses, and quartz were investigated. The experimental results allow the determination of phonon lifetimes $\ensuremath{\tau}$ and of elasto-optic constants. In our amplifier system, accurate values of $\ensuremath{\tau}$ are obtained for $\ensuremath{\tau}l3$ nsec, i.e., for liquids and some solids. The limitation of the method is discussed. In absorbing media, stimulated thermal Brillouin scattering was observed in quantitative agreement with theory.

Wentzel-Kramers-Brillouin method in the Bargmann representation. [of quantum mechanics

Abstract: It is demonstrated that the Bargmann representation of quantum mechanics is ideally suited for semiclassical analysis, using as an example the WKB method applied to the bound-state problem in a single well of one degree of freedom. For the harmonic oscillator, this WKB method trivially gives the exact eigenfunctions in addition to the exact eigenvalues. For an anharmonic well, a self-consistent variational choice of the representation greatly improves the accuracy of the semiclassical ground state. Also, a simple change of scale illuminates the relationship of semiclassical versus linear perturbative expansions, allowing a variety of multidimensional extensions.

Observation of Dirac-like energy band and ring-torus Fermi surface associated with the nodal line in topological insulator CaAgAs

Abstract: One of key challenges in current material research is to search for new topological materials with inverted bulk-band structure. In topological insulators, the band inversion caused by strong spin–orbit coupling leads to opening of a band gap in the entire Brillouin zone, whereas an additional crystal symmetry such as point-group and nonsymmorphic symmetries sometimes prohibits the gap opening at/on specific points or line in momentum space, giving rise to topological semimetals. Despite many theoretical predictions of topological insulators/semimetals associated with such crystal symmetries, the experimental realization is still relatively scarce. Here, using angle-resolved photoemission spectroscopy with bulk-sensitive soft-x-ray photons, we experimentally demonstrate that hexagonal pnictide CaAgAs belongs to a new family of topological insulators characterized by the inverted band structure and the mirror reflection symmetry of crystal. We have established the bulk valence-band structure in three-dimensional Brillouin zone, and observed the Dirac-like energy band and ring-torus Fermi surface associated with the line node, where bulk valence and conducting bands cross on a line in the momentum space under negligible spin–orbit coupling. Intriguingly, we found that no other bands cross the Fermi level and therefore the low-energy excitations are solely characterized by the Dirac-like band. CaAgAs provides an excellent platform to study the interplay among low-energy electron dynamics, crystal symmetry, and exotic topological properties. An angle-resolved photoemission spectroscopy study reveals a novel topological phase with band crossing on a line at the Fermi surface in hexagonal pnictide CaAgAs. A team led by Takafumi Sato from Tohuku University in Japan performed angle-resolved photoemission spectroscopy measurements on hexagonal pnictide CaAgAs with mirror reflection symmetry. They observed inverted band structure, which is the Dirac-like bands of a topological material, at a line node giving rise to a ring-torus Fermi surface in the momentum space. There are no other bands crossing the Fermi level so the low-energy excitations are solely characterized by the Dirac-like bands. These features make CaAgAs a promising candidate for studying the interplay among mirror symmetry, low-energy excitations and transport properties in topological semimetals.

Helical Fermi arcs and surface states in time-reversal invariant Weyl semimetals

Abstract: Weyl semimetals are gapless three-dimensional topological materials where two bands touch at an even number of points in the Brillouin zone. In this work we study a zinc-blende lattice model realizing a time-reversal invariant Weyl semimetal. The bulk dynamics is described by 12 helical Weyl nodes. Surface states form a peculiar quasi-two-dimensional helical metal fundamentally different from the Dirac form typical for topological insulators. The allowed direction of velocity and spin of low-energy surface excitations are locked to the cubic symmetry axes. The studied system illustrates the general properties of surface states in systems with common crystal symmetries.

Short light pulse amplification and compression by stimulated Brillouin scattering in plasmas in the strong coupling regime

Abstract: Short light pulse amplification using the stimulated Brillouin backscattering mechanism is considered. The novel feature is that the interaction process takes place in the strongly coupled regime and therefore the pulse compression is not limited by the ion-acoustic wave period. The mechanism is very efficient due to the large ratio of light frequency to the characteristic ion-acoustic wave frequency. Although large-amplitude ion-acoustic waves are generated and subsequent wave breaking takes place, the fluid and kinetic nonlinearities do not intervene with the amplification itself.