Brillouin zone

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

Spin-wave eigenmodes of permalloy squares with a closure domain structure.

Abstract: Quantized spin-wave eigenmodes in single, 16 nm thick and 0.75 to $4\text{ }\ensuremath{\mu}\mathrm{m}$ wide square permalloy islands with a fourfold closure domain structure have been investigated by microfocus Brillouin light scattering spectroscopy and time resolved scanning magneto-optical Kerr microscopy. Up to six eigenmodes were detected and classified. The main direction of the spin-wave quantization in the domains was found to be perpendicular to the local static magnetization. An additional less pronounced quantization along the direction parallel to the static magnetization was also observed.

The electronic structure of liquid water within density-functional theory.

Abstract: In the last decade, computational studies of liquid water have mostly concentrated on ground-state properties. However, recent spectroscopic measurements have been used to infer the structure of water, and the interpretation of optical and x-ray spectra requires accurate theoretical models of excited electronic states, not only of the ground state. To this end, we investigate the electronic properties of water at ambient conditions using ab initio density-functional theory within the generalized gradient approximation (DFT/GGA), focusing on the unoccupied subspace of Kohn-Sham eigenstates. We generate long (250 ps) classical trajectories for large supercells, up to 256 molecules, from which uncorrelated configurations of water molecules are extracted for use in DFT/GGA calculations of the electronic structure. We find that the density of occupied states of this molecular liquid is well described with 32-molecule supercells using a single k point (k=0) to approximate integration over the first Brillouin zone. However, the description of the unoccupied electronic density of states (u-EDOS) is sensitive to finite size effects. Small, 32-molecule supercell calculations, using the Gamma-point approximation, yield a spuriously isolated state above the Fermi level. Nevertheless, the more accurate u-EDOS of large, 256-molecule supercells may be reproduced using smaller supercells and increased k-point sampling. This indicates that the electronic structure of molecular liquids such as water is relatively insensitive to the long-range disorder in the molecular structure. These results have important implications for efficiently increasing the accuracy of spectral calculations for water and other molecular liquids.

Surface electronic structure of GaAs(001)-(2×4): Angle-resolved photoemission and tight-binding calculations

Abstract: We have carried out an experimental and theoretical study of the surface-energy-band structure of the As-stable GaAs(001)-(2\ifmmode\times\else\texttimes\fi{}4) reconstruction. Angle-resolved photoemission measurements with the use of synchrotron radiation at LURE, Orsay, have been performed on surfaces which were grown in situ by molecular beam epitaxy. Measurements made at high-symmetry points and along symmetry lines of the surface Brillouin zone show weakly dispersing dangling-bond-like surface states in the energy range between - 1.6 eV and the top of the valence band, and a nearly dispersionless state near - 3 eV. To clarify the origin of these states, we have applied the scattering theoretical method on the basis of an empirical tight-binding description of the GaAs bulk crystal to the ideal (1\ifmmode\times\else\texttimes\fi{}1) As-terminated surface and to a (2\ifmmode\times\else\texttimes\fi{}1) asymmetric As-As dimer model. The principal effect of the reconstruction is the introduction of a new dimer-related state at - 3.5 eV. In addition in the energy range near the top of the projected bulk bands, dangling-bond states with a significant in-plane component are found. Although we do not observe a direct one-to-one correspondence between experiment and theory, the essential features of an asymmetric As-As dimer are established.

Topological collective plasmons in bipartite chains of metallic nanoparticles

Abstract: We study a bipartite linear chain constituted by spherical metallic nanoparticles, where each nanoparticle supports a localized surface plasmon. The near-field dipolar interaction between the localized surface plasmons gives rise to collective plasmons, which are extended over the whole nanoparticle array. We derive analytically the spectrum and the eigenstates of the collective plasmonic excitations. At the edge of the Brillouin zone, the spectrum is of a pseudorelativistic nature similar to that present in the electronic band structure of polyacetylene. We find the effective Dirac Hamiltonian for the collective plasmons and show that the corresponding spinor eigenstates represent one-dimensional Dirac-like massive bosonic excitations. Therefore, the plasmonic lattice exhibits similar effects to those found for electrons in one-dimensional Dirac materials, such as the ability for transmission with highly suppressed backscattering due to Klein tunneling. We also show that the system is governed by a nontrivial Zak phase, which predicts the manifestation of edge states in the chain. When two dimerized chains with different topological phases are connected, we find the appearance of the bosonic version of a Jackiw-Rebbi midgap state. We further investigate the radiative and nonradiative lifetimes of the collective plasmonic excitations and comment on the challenges for experimental realization of the topological effects found theoretically.

Gaps and kinks in the electronic structure of the superconductor 2H-NbSe2 from angle-resolved photoemission at 1 K

Abstract: Angle-resolved photoemission spectroscopy at a temperature of 1 K is used to determine the wave-vector dependence of the spectral gap and band renormalization due to electron-phonon coupling in the layered chargedensity-wave superconductor 2H -NbSe2. The measured gap size and coupling parameter are Fermi-surface-sheet dependent and anisotropic. The largest energy gap, highest coupling strength, and strongest variation in both quantities are found on the double-walled Nb 4d-derived Fermi-surface sheet that is centered on the corners of the hexagonal Brillouin zone. On this sheet, the spectral gap has two distinct anticorrelated components associated with superconductivity and the charge-density wave. The results establish 2H -NbSe2 as a moderately correlated intermediate-coupling anisotropic multigap superconductor.