Discrete breathers in a fl-FPUT square lattice from in-band external driving

The absorption of energy by a fl-Fermi-Pasta-Ulam-Tsingu square lattice from harmonically driven rows of particles is studied numerically in a wide range of driving frequencies Q and for relatively small driving amplitudes A. Two mechanisms of energy transfer in the lattice are described depending on the driving parameters Q and A. When Q is deep inside the phonon band, an extended wave is emitted from the driven row of particles. Interestingly, at the front, the emitted wave splits into wavepackets having fundamental frequency slightly larger than the driving frequency. When Q is close to the upper edge of the phonon band wmaxbut still within the band, the frequency of the wavepackets emitted by the driven row of particles is above the phonon band. Such wavepackets are actually discrete breathers (DBs). Thus, it is shown that DBs can contribute to energy transfer in the lattice not only when the driving frequency is outside the phonon band, as in classical supratransmission, but also when it is inside the phonon band. In classical supratransmission, the excitation of DBs can only be observed when the driving amplitude is above a threshold. This is also true for in -band driving, and the threshold driving amplitude decreases as the driving frequency approaches the phonon band edge.