Moving Gap Discrete Breather in Biatomic Crystal

The biatomic crystal with CsCl structure is considered with the interatomic interactions described by the $\beta$-Fermi-Pasta-Ulam-Tsingou potential. The case of a large difference in the atomic masses of the components is analyzed when there is a gap in the phonon spectrum of the crystal. A spatially localized large-amplitude vibrational mode, called the discrete breather (DB), is found by applying a localization function to the delocalized nonlinear vibrational mode (DNVM). The DNVM and consequently the DB have frequencies in the gap of the phonon spectrum. It is shown that the DB can be set in motion using a physically motivated ansatz.