Odd-parity mode frequency and lifetime.

For sufficiently small amplitude, the frequency of the mode lies close to the optic plane wave band. With increasing amplitude the mode becomes sufficiently localized so that both the ac and the dc components are concentrated in the vicinity of the central particle. The ac vibrational pattern of such a gap mode is displayed in the figure. When the amplitude of the central particle becomes even larger, A/d > 0.2, its frequency crosses into the acoustic band and its eigenvector converts to a band mode [1].
The frequency of an anharmonic gap mode in a diatomic lattice as a function of normalized amplitude, A/d. The odd-parity mode is centered at the light atom. The molecular dynamics simulation results are represented by squares while the analytic results are given by the solid line. The triatomic molecule approximation is represented by the dashed line.
[1] S. A. Kiselev, S. R. Bickham and A. J. Sievers, Phys. Lett. A 184, 255 (1993).

Last modified: August 10, 1997