Discrete breathers in crystals: Energy localization and transport

Discrete breather (DB) is spatially localized vibrational mode in defect-free nonlinear lattice. Frequency of DB must lie outside the spectrum of small-amplitude traveling waves. It neither does resonate with traveling waves and nor does it lose energy to their excitation. Theoretically DB can maintain its vibrational energy forever in the absence of thermal vibrations and other perturbations. Crystals are nonlinear discrete systems and they also support existence of DB. Experimental studies of DB run into considerable technical difficulties, and the main tool of their study is by far the atomistic computer simulations. Having gained confidence in the existence of DB in crystals, we still poorly understand their role in solid state physics. This review covers issues specific to the physics of real crystals, which were not considered in the classical works on DB. Focus is placed on the energy transport through crystal lattice assisted by moving DB and by energy exchange between DB.