Anomalous phonon branch

A. Nagasawa, R. Yamauchi, K. Kita, T. Makita and Y. Morii, [110)TA phonon branch and anomalous... 

The calculated Rayleigh mode (SJ, the lowest lying phonon branch, is in good agreement with the experimental data of Harten et al. for all three metals. Due to symmetry selection rules the shear horizontal mode just below the transverse bulk band edge can not be observed by scattering methods. The mode denoted by Sg is the anomalous acoustic phonon branch discussed above. Jayanthi et al. ascribed this anomalous soft resonance to an increased Coulomb attraction at the surface, reducing the effective ion-ion repulsion of surface atoms. The Coulomb attraction term is similar for all three metals... 

For a harmonic crystal the phonon lifetime is infinite and there is no scattering of thermal phonons.To understand the mechanism on how the guest-host interactions lead to the anomalous temperature dependence of the thermal conductivity, the lifetimes were calculated for phonon-phonon scatterings as a result of the anharmonic terms in the xenon-water potential of xenon hydrate in the small and large cage. The inverse relaxation time (lifetime), of a lattice vibration with frequency C0j q) (/ is the branch index and q is the direction of the momentum transfer) is related to the transition rate, W, of the lattice wave scattered from state qj q f by a defect according to, ... 

---