In a one-dimensional monatomic lattice with both positive quadratic
and quartic nearest-neighbor interaction potential the intrinsic
odd-parity  and even parity  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 ;
however, diatomic lattices with the same interparticle interaction
potentials do possess anharmonic gap modes with frequencies between
acoustic and optic bands . Both stationary and moving intrinsic
anharmonic gap modes can be generated in diatomic lattices.
 A.J.Sievers and S.Takeno, Phys. Rev. Lett. 61, 970 (1988).
 J. B. Page, Phys. Rev. B 41, 7835 (1990).
 S. R. Bickham, S. A. Kiselev, and A. J. Sievers, Physics Review B,
47 14206 (1993).
 S. A. Kiselev, S. R. Bickham, and A. J. Sievers, Physics Review B,
48 13508-11 (1993).
Last modified: August 12, 1997