QUANTUM BREATHERS IN ELECTRON-PHONON SYSTEMS

Quantum breathers are studied numerically in several electron-phonon c oupled finite chain systems, in which the coupling results in intrinsi c nonlinearity but with varying degrees of nonadiabaticity. As for qua ntum nonlinear lattice systems, we find that quantum breathers can exi st as eigenstates of the system Hamiltonians. Optical responses are ca lculated as signatures of these coherent nonlinear excitations. We pro pose a new type of quantum nonlinear excitation, ''breather excitons,' ' which are bound states of breathers and excitons, whose properties a re clarified with a minimal exciton-phonon model.