Acoustic Phonon Velocity Research Articles

Soliton diffusion in polyacetylene. III. Low-temperature regime

The soliton diffusion in the temperature region $Tl{T}_{0}(\ensuremath{\equiv}2m{c}^{2})$ is analyzed theoretically within the Su, Schrieffer, and Heeger model. Here $m$ is the soliton mass and $c$ is the acoustic-phonon velocity. It is shown that the diffusion constant increases exponentially like $\mathrm{exp}(\frac{{T}_{0}}{T})$ as the temperature $T$ is decreased below ${T}_{0}$. This temperature dependence appears to be consistent with some of the recent nuclear-magnetic-resonance experiments in pristine polyacetylene.

Soliton diffusion in polyacetylene. II. Acoustic phonons

The soliton diffusion due to the coupling to acoustic phonons in polyacetylene is analyzed theoretically within the Su, Schrieffer, and Heeger model. It is shown that in the temperature region $T\ensuremath{\ll}\frac{1}{2}{\ensuremath{\omega}}_{0}$, where ${\ensuremath{\omega}}_{0}$ (\ensuremath{\sim}2000 K) is the optical-phonon frequency, the acoustic phonon dominates the soliton damping. Furthermore, for $T\ensuremath{\gg}{T}_{0}$, the single-phonon process dominates the soliton diffusion where ${T}_{0}=2m{c}^{2}$, and $m$ and $c$ are the soliton mass and the acoustic-phonon velocity, respectively. The one-dimensional model predicts the temperature-dependent diffusion constant $D\ensuremath{\propto}{T}^{\frac{1}{2}}$, while the three-dimensional model predicts $D\ensuremath{\propto}{T}^{\ensuremath{-}\frac{1}{2}}$. The latter temperature dependence appears to be consistent with some of the recent nuclear-magnetic-resonance experiments.

Investigation of acoustic phonons in CsNiF3by Brillouin scattering

Brillouin scattering measurements were made to determine the velocities of acoustic phonons and the values of the elastic coefficients of CsNi${\mathrm{F}}_{3}$. Temperature dependence of ${C}_{11}$ and ${C}_{33}$ was investigated between 4 and 300 K. In contradiction with the earlier measurement of Young's modulus along the $c$ axis of the crystal, ${C}_{33}$ was found to have a negative thermoelastic coefficient. In connection with these measurements the dispersion of the refractive index was also determined.

Elastic constants of SrClF and BaClF crystals

Abstract The six elastic constants of SrClF and BaClF crystals are calculated from the acoustic phonon velocities computed in four symmetry directions using the shell model of lattice dynamics.

Velocity of high frequency sound waves in oriented DNA fibres and films determined by Brillouin scattering

We have measured the velocity of acoustic microwave phonons in fibres and films of oriented DNA. The sound velocity is found to be surprisingly isotropic and to decrease substantially during hydration of DNA. No optical modes have been detected in the frequency range covered from 5 to 120 GHz. The photoelastic constants are strongly anisotropic.

Vibrational Edge Modes for Small-Angle Wedges

Moss, Maradudin, and Cunningham recently calculated the velocities of long-wavelength acoustic phonons localized at the apex of a variable-angle semi-infinite elastic wedge. We present here a method by which more precise results may be obtained for small wedge angles.

On the correction for thermal diffuse scattering in measured integrated intensities from cubic single crystals

An expression is obtained for the spherically averaged acoustic phonon polarization and velocity factor found in theories of 1-phonon thermal diffuse scattering that is valid for all real cubic crystals and easy to evaluate numerically. A comparison with the usual approximate form shows appreciable discrepancies for very anisotropic materials.