Transitive coupled electron-phonon systems

Michele Fabrizio, Claudio Castellani, C. Di Castro

We consider a one-dimensional system of electrons interacting via a short-range repulsion and coupled to phonons close to the metal-insulator transition at half-filling. We argue that the metal-insulator transition can be described as a standard one-dimensional incommensurate to commensurate transition, even if the electronic system is coupled to the lattice distortion. By making use of known results for this transition, we prove that low-momentum phonons, with the inclusion of the 4kF (≃2π near half-filling) scattering, do not play any relevant role close to the metal-insulator transition, unless their coupling to the electrons is large in comparison with the other energy scales present in the problem. In other words the effective strength of the low-momentum transferred electron-phonon coupling does not increase close to the metal-insulator transition, even though the effective velocity of the mobile carriers is strongly diminished.

Eric Jeckelmann, Chunli Zhang, Steven R. White

Leonard Ruocco, Mona Berciu, Jeff F. Young

Electromagnetically coupled two-level systems play a central role in several condensed matter components being considered for quantum information processing applications. If the states couple to phonon excitations, their electromagnetic response is altered via phonon-assisted transitions and lifetime broadening. The former has been treated extensively for a number of specific two-level systems (e.g., excitons in artificial quantum dots, localized states associated with impurities or defects, etc.), but the latter has received less attention. Here we study a microscopic model of the dipole transition of a two-level system under the influence of both diagonal and nondiagonal interactions with a bath of phonons. Our results capture both the influence of the frequency distribution of phonons on the relative spectral weight of the zero-phonon transition and the phonon sidebands, and the broadening of the zero-phonon line due to nondiagonal electron-phonon coupling. We use a formalism that includes non-Markovian effects related to the feedback mechanism between the two-level system and the phonon bath. For simplified forms of the phonon spectral functions we provide analytical expressions up to second order in the coupling strength that demonstrate the importance of including both forms of electron-phonon coupling in studies of these systems. Our formalism can be generalized to higher orders of coupling and for realistic phonon spectral functions.

Wang Ganquan, DeChang Dai, Qi Luo +2 more

The 4f electronic transition accompanied by electron-phonon interaction was studied through the Brownian oscillator model in Nd: YAG. The expression of electron-phonon coupling was derived, the excitation spectroscopies of different electron-phonon coupling constants were calculated and the results indicated the absorption peak of phonon in two sides of electronic peak is produced by electron-phonon coupling. The stronger electron-phonon coupling, the more phonon peaks. Through excitation spectroscopy simulation, the electron-phonon coupling constant and phonon frequency were obtained. From these data, the theoretical time resolved coherent spectroscopy was calculated and is good agreement with experiment result. It also indicated that the electron-phonon coupling in rare earth ion's 4f electronic transition is weak because of the smaller constant of electron-phonon coupling compared with that of semiconductor.