Breathers in one-dimensional nonlinear thermalized lattice with an energy gap

We study a model of a nonlinear lattice with an on-site potential that induces a breather gap, i.e. a frequency interval where breathers are unstable. The gap is determined numerically and after thermalization of the system we compute power spectra of local displacements. We find that the gap is clearly manifested at small couplings through a large spectral contribution in the linearized phonon region that is not shifted strongly with temperature.