Power spectrum

Power spectrum of odd-parity anharmonic gap modes in a diatomic lattice. The numerical simulations are for 601 particles. Panels (a) and (b) show the spectra of the gap modes with the amplitudes A/d=0.1 and A/d=0.2, respectively. They are obtained over the time intervals T=256Tm, where Tm is the vibrational period of highest frequency plane wave mode.
Because the symmetry of the odd-parity mode should eliminate even harmonics in the power spectrum of the gap mode vibration, the results in panel (a) indicate that the localized mode is translating between one site and its neighbor in the next unit cell. In moving, the mode takes on an even-parity character for part of the time and even harmonics in the power spectrum are permitted in this case. This slow transformation from one site to the next also produces the quasi-dc component in panel (a). The extra noise observed for panel (b) is attributed to the emission of plane waves by the gap mode.
Last modified: August 12, 1997