Brillouin zone

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

Structural, elastic and lattice dynamical properties of the alkali metal tellurides: First-principles study

Abstract: We report a detailed first-principles density functional calculations to understand the systematic trends for crystal structure, elastic and lattice dynamical properties of the anti-fluorite alkali metal tellurides M2Te depending from the type of the M cations (M are Li, Na, K and Rb). The calculated equilibrium lattice parameters are in very good agreement with the available experimental data. Single-crystal and polycrystalline elastic moduli and their related properties of the title compounds were calculated via the stress-strain method. The relatively weak values of the calculated elastic moduli demonstrate the weak resistance of these compounds to applied external forces. Phonon dispersion curves throughout the Brillouin zone and corresponding density of states were calculated using the linear response approach. No imaginary phonon modes were found, which indicate the dynamical stability of the examined materials. The atomic displacements at Γ point were determined. Low-frequency dielectric properties and infrared response were investigated.

Metal-insulator transition on the Ge(001) surface

Abstract: High-resolution angle-resolved photoemission studies of the Ge(001) surface are reported which clearly indicate the existence of a metallic surface state whose emission is observed over a narrow range of parallel momenta near the center of the surface Brillouin zone. The state slowly disappears as the temperature is lowered from room temperature to 77 K. This metal-insulator transition is coincident with a recently predicted and observed transition from a disordered to an ordered $c(4\ifmmode\times\else\texttimes\fi{}2)$ structure.

Fragility and compressibility at the glass transition

Abstract: Isothermal compressibilities and Brillouin sound velocities from the literature allow us to separate the compressibility at the glass transition into a high-frequency vibrational and a low-frequency relaxational part. Their ratio shows the linear fragility relation discovered by x-ray Brillouin scattering, though the data bend away from the line at higher fragilities. Using the concept of constrained degrees of freedom, one can show that the vibrational part follows the fragility-independent Lindemann criterion; the fragility dependence seems to stem from the relaxational part. The physical meaning of this finding is discussed.

A comprehensive multiphonon spectral analysis in MoS 2

Abstract: We present a comprehensive multiphonon Raman and complementary infrared analysis for bulk and monolayer MoS2. For the bulk the analysis consists of symmetry assignment from which we obtain a broad set of allowed second-order transitions at the high symmetry M, K and Γ Brillouin zone (BZ) points. The attribution of about 80 transitions of up to fifth order processes are proposed in the low temperature (95 K) resonant Raman spectrum measured with excitation energy of 1.96 eV, which is slightly shifted in energy from the A exciton. We propose that the main contributions come from four phonons: A1g (M), E12g (M1), E22g (M1) (TA' (M)) and E22g (M2) (LA' (M)). The last three are single degenerate phonons at M with an origin of the E12g (Γ) and E22g (Γ) phonons. Among the four phonons, we identify in the resonant Raman spectra all (but one) of the second-order overtones, combination and difference-bands and many of the third order bands. Consistent with the expectation that at the M point only combinations with the same inversion symmetry (g or u) are Raman-allowed, the contribution of combinations with the longitudinal acoustic (LA(M)) mode can not be considered with the above four phonons. Although minor, contributions from K point and possibly Γ-point phonons are also evident. The '2LA band', measured at ~460 cm−1 is reassigned. Supported by the striking similarity between this band, measured under off-resonant conditions, and recently published two phonon density of states, we explain the lower part of the band, previously attributed to 2LA(M), as being due to a van Hove singularity between K and M. The higher part, previously attributed exclusively to the A2u (Γ) phonon, is mostly due to the LA and LA' phonons at M. For the monolayer MoS2 the second-order phonon processes from the M and Γ BZ points are also analyzed and are discussed within similar framework to that of the bulk.