Phonon-induced Dephasing Research Articles

Phonon-induced dephasing of localized optical excitations.

The dynamics of strongly localized optical excitations in semiconductors is studied including electron-phonon interaction. The coupled microscopic equations of motion for the interband polarization and the carrier distribution functions contain coherent and incoherent contributions. While the coherent part is solved through direct numerical integration, the incoherent one is treated by means of a generalized Monte Carlo simulation. The approach is illustrated for a simple model system. The temperature and excitation energy dependence of the optical dephasing rate is analyzed and the results are compared to those of alternative approaches. \textcopyright{} 1996 The American Physical Society.

Phonon-induced dephasing of the internal vibrational mode of a diatomic adsorbed molecule.

The line shape of an internal vibrational mode of an adsorbed molecule can be determined in part by dephasing processes due to anharmonic interactions with lower-frequency vibrational modes of the molecule and substrate. Perturbative and exact treatments of the bilinear coupling between the molecule and the surface atoms are compared, for the case in which the lower-frequency molecular vibration is degenerate with the phonon continuum. Line broadening and frequency shifts are calculated explicitly in a model in which the admolecule is constrained to move perpendicularly to the surface. It is found that the magnitude and sign of the temperature-dependent frequency shift depend sensitively on the shape of the adsorption potential, and that the exact treatment of the bilinear interaction leads to substantial improvements, compared to the purely perturbative treatment. Limitations on the applicability of the exchange model for dephasing are discussed.

Optical dephasing of the electronic transitions of delocalized molecular dimer states

We present a theoretical study of the optical dephasing of the electronic transitions of delocalized molecular dimer states. The dephasing arises from the dynamical interactions of the dimer states with the phonon bath of the host crystal. We introduce a general dephasing model for dimers with strong intermolecular interactions and analyze the consequences of the model with optical Redfield theory. A quantum mechanical microscopic model is developed in which the interaction Hamiltonian of the dimer states and the phonon bath states is clearly delineated. We treat both linear and quadratic excitation-phonon coupling in which the two molecules comprising the dimer may be coupled differently to the phonons. Couplings to acoustic, optical, and pseudolocal phonons (librations) are considered explicitly. The temperature dependence of the dephasing rates are obtained for scattering between delocalized dimer states, scattering to dimer librations and phonon-induced pure dephasing. These results are used to analyze the photon echo studies on pentacene dimers and tetracene dimers in p-terphenyl and on naphthalene dimers in perdeuteronaphthalene. In the pentacene dimers and tetracene dimers, we conclude that the dephasing results from scattering to the dimer librations via a one-phonon process. In addition, a quantitative value for the libron–phonon coupling is determined. In the naphthalene dimer system, we find scattering between delocalized dimer states, induced by linear excitation-phonon coupling, to be the predominant dephasing mechanism. A quantitative value is determined for the phonon coupling matrix element responsible for scattering between the delocalized states.