Moving intrinsic gap mode

Displacements of particles involved in a moving anharmonic gap mode at three different times. The mode is excited at T=0, then viewed at T=8Tm and T=16Tm where Tm is the vibrational period of highest frequency plane wave mode. At T=0 the odd-parity mode with the amplitude A/d=0.005 is centered at the light particle (at site number 100) in a diatomic lattice (m=39amu, M=80amu) containing 201 particles with fixed boundary conditions. The light particles in the chain are represented by small circles and the heavy ones by squares.
Velocities of particles involved in a moving anharmonic gap mode at three different times. The lowest curve corresponds to the maximum velocity of the odd-parity mode centered at site 100 and the upper curve shows the odd-parity mode with the maximum velocity centered at site 102. The middle curve shows an even-parity-mode pattern which takes place at the intermediate time. At this particular time the particles at sites 100 and 102 have maximal but opposite velocities. This illustration demonstrates that as the mode moves through the lattice it passes sequentially through the displacement patterns of even- and odd-parity, a result similar to that first observed for an anharmonic local mode in a simple monatomic lattice with hard quartic potential [1].
[1] K. W. Sandusky, J. B. Page and K. E. Schmidt, Phys. Rev. B 46, 6161 (1992).

Last modified: August 10, 1997