Effect of the interatomic potential stiffness on the properties of gap discrete breathers in 2D biatomic Morse crystal

Abstract

Discrete breathers (DB) are spatially localized nonlinear vibrational modes in discrete lattices. The latest trend is the study of DB in various crystals. Many studies have been done recently for the two-dimensional (2D) model of crystal with Morse interatomic potentials. Two types of DB have been discussed for Morse crystals, the gap DB with soft type of nonlinearity and the hard-type anharmonicity DB with frequency above the phonon spectrum. Here we focus on the analysis of the effect of rigidity of the Morse potential on the properties of gap discrete breathers in the 2D biatomic crystal model of composition A3B. Atoms A are ten times heavier than atoms B and this is the reason of the presence of a wide gap in the phonon spectrum of the crystal. The same Morse potentials are used to describe the A-A, B-B, and A-B interactions. Two of the three Morse potential parameters are fixed to unity without the loss of generality. For the third parameter, which defines the stiffness of the interatomic bond, two different values are considered. In both cases two polarizations of DB are investigated. It was found that for a smaller stiffness of the interatomic bond DB have larger maximal amplitude, regardless the type of polarization. On the other hand, they demonstrate a higher rate of radiation of the small-amplitude waves and thus, they have smaller lifetime.