Introduction
In a one-dimensional monatomic lattice with both positive quadratic
and quartic nearest-neighbor interaction potential the intrinsic
odd-parity [1] and even parity [2] local modes appear above the top of
the plane wave spectrum.
When a cubic term is added to the interatomic potential, with
increasing amplitude, the frequency of a stationary local mode
decreases until it approaches the cutoff plane wave frequency, where
the mode becomes unstable.
Examination of 1-D lattices with the Toda, Born-Mayer, Lennard-Jones
or Morse two-body interatomic potentials demonstrates that intrinsic
local modes do not appear above the top of plane wave spectrum [3];
however, diatomic lattices with the same interparticle interaction
potentials do possess anharmonic gap modes with frequencies between
acoustic and optic bands [4]. Both stationary and moving intrinsic
anharmonic gap modes can be generated in diatomic lattices.
[1] A.J.Sievers and S.Takeno, Phys. Rev. Lett. 61, 970 (1988).
[2] J. B. Page, Phys. Rev. B 41, 7835 (1990).
[3] S. R. Bickham, S. A. Kiselev, and A. J. Sievers, Physics Review B,
47 14206 (1993).
[4] S. A. Kiselev, S. R. Bickham, and A. J. Sievers, Physics Review B,
48 13508-11 (1993).
Last modified: August 12, 1997