GENERATION OF SUPERSONIC AND SUBSONIC SOLITONS IN THE FERMI-PASTA-ULAM CHAIN

The dynamics of the Fermi-Pasta-Ulam chain with quartic anharmonicity are numerically investigated by means of a stimulating force of Gaussi an time shape, which acts on a single atom. Depending on the strength and duration of this force, several phenomena have been observed. A pu lse of originally continuous envelope disintegrates into solitary obje cts ('multifurcative process'), which may be ultrasonic solitons of ki nk type, or subsonic and self-localized solitons of oscillating nature . In the oscillations of the latter two, frequencies are involved, abo ve the Debye frequency, and the spatial envelope displays a 'breathing ' behaviour. Some analytical background is also presented.