Y P Joshi
Articles written in Pramana – Journal of Physics
Volume 18 Issue 1 January 1982 pp 59-71 Solid State Physics
We present the calculation of phonon life time at low frequencies in an amorphous solid, which is assumed to be characterized by an elasticity that exhibits spatial fluctuation. Thermodynamic Green’s function method is used to compute phonon self-energy, and an iterative method is devised to obtain an improvement upon the first order perturbation calculation. The elasticity correlation is taken to be an exponentially falling function of distance. We obtain an inverse life time that varies as the fourth power of phonon frequency for small values of the latter, and whose frequency-dependence becomes weaker and weaker as the frequency increases.
Volume 18 Issue 6 June 1982 pp 461-472 Solid State Physics
Thermal conductivity of a cubic crystal in the boundary scattering regime is calculated, taking into account the difference between the phonon phase and group velocities. Numerical estimates in the case of silicon indicate appreciable anisotropy in conductivity as a result of phonon focussing, its maximum value being about 90% larger than the minimum. The contributions of the individual polarization branches are found to be more strongly dependent on direction than the total conductivity. It is further observed that the angle between the phonon phase and group velocities can be sometimes as large as 10°, 24° and 18° in the case of the longitudinal and the two transverse acoustic branches, respectively.
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