  We investigate transient nonlinear localization, namely the self-excitation
of energy bursts in an atomic lattice at finite temperature. As a basic model
we consider the diatomic Lennard-Jones chain. Numerical simulations suggest
that the effect originates from two different mechanisms. One is the thermal
excitation of genuine discrete breathers with frequency in the phonon gap. The
second is an effect of nonlinear coupling of fast, lighter particles with slow
vibrations of the heavier ones. The quadratic term of the force generate an
effective potential that can lead to transient grow of local energy on time
scales the can be relatively long for small mass ratios. This heuristics is
supported by a multiple-scale approximation based on the natural time-scale
separation. For illustration, we consider a simplified single-particle model
that allows for some insight of the localization dynamics.
