Brillouin zone

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

A Brillouin scattering study of the hydration of Li- and Na-DNA films.

Abstract: We have used Brillouin spectroscopy to study the velocities and attenuation of acoustic phonons in wet-spun films of Na-DNA and Li-DNA as a function of the degree of hydration at room temperature. Our data for the longitudinal acoustic (LA) phonon velocity vs water content display several interesting features and reveal effects that we can model at the atomic level as interhelical bond softening and relaxation of the hydration shell. The model for interhelical softening makes use of other physical parameters of these films, which we have determined by gravimetric, x-ray, and optical microscopy studies. We extract intrinsic elastic constants for hydrated Na-DNA molecules of c11 ≃ 8.0 × 1010 dynes/cm2 and c33 ≃ 5.7 × 1010 dynes/cm2, which corresponds to a Young's modulus, E ≃ 1.1 × 1010 dynes/cm2 (with Poisson's ratio, σ = 0.44). The negative velocity anisotropy of the LA phonons indicates that neighboring DNA molecules are held together by strong interhelical bonds in the solid state. The LA phonon attenuation data can be understood by the relaxational model in which the acoustic phonon is coupled to a relaxation mode of the water molecules. Na-DNA undergoes the A to B phase transition at a relative humidity (rh) of 92% while Li-DNA (which remains in the B form in this range) decrystallizes at an rh of 84%. We find that our Brillouin results for Na- and Li-DNA are remarkably similar, indicating that the A to B phase transition does not play an important role in determining the acoustic properties of these two types of DNA.

Lattice dynamical, dielectric, and thermodynamic properties of β-Ga2O3 from first principles

Abstract: Lattice dynamical, dielectric, and thermodynamic properties of β-Ga2O3 are investigated by first principles. The calculated phonon frequencies for the Raman-active and the infrared-active modes are assigned. The phonon dispersion curves along high symmetry lines in the Brillouin zone and the phonon density of states are also calculated. The electronic and static dielectric tensors are calculated. The calculated static dielectric constants are much larger than the electronic constants, showing the rather strong ionic contributions to static dielectric constants. These calculated results are in a good agreement with available experimental values. The thermodynamic functions are calculated by using the phonon density of states.

Vibrations in binary and ternary topological insulators: First-principles calculations and Raman spectroscopy measurements

Abstract: Density-functional perturbation theory and Raman spectroscopy are used in the study of vibrations in bulk V${}_{2}$VI${}_{3}$ binary and ternary topological insulators as well as in ultrathin films composed of one and two quintuple layers. Full dispersion curves along the Brillouin zone symmetry directions are calculated and analyzed and the zone-center Raman active modes are compared to the experimental results. The calculations of the two quintuple layer films reveal modes that correspond to displacements of entire quintuple layer blocks. These modes have low frequencies and are Raman active. The phonon dispersion curves of one and two quintuple layer Bi${}_{2}$Se${}_{3}$ films are compared with recent helium atom scattering experiments [Phys. Rev. Lett. 107, 186102 (2011)].

Topological currents in black phosphorus with broken inversion symmetry

Abstract: We examine the nature of topological currents in black phosphorus when its inversion symmetry is deliberately broken. Here, the conduction- and valence-band edges are located at the $\mathrm{\ensuremath{\Gamma}}$ point of the rectangular Brillouin zone, and they exhibit strong anisotropy along its two crystal axes. We will show below that these salient features lead to linear transverse neutral topological currents, accompanied also by nonlinear transverse charge currents at the Fermi surface. These topological currents are maximal when the in-plane electric field is applied along the zigzag crystal axes but zero along the armchair direction.