Exciton-Phonon Interaction and Relaxation Times from First Principles

Abstract

Electron-phonon interactions are key to understanding the dynamics of electrons in materials and can be modeled accurately from first principles. However, when electrons and holes form Coulomb-bound states (excitons), quantifying their interactions and scattering processes with phonons remains an open challenge. Here we show a rigorous approach for computing exciton-phonon (ex-ph) interactions and the associated exciton dynamical processes from first principles. Starting from the ab initio Bethe-Salpeter equation, we derive expressions for the ex-ph matrix elements and relaxation times. We apply our method to bulk hexagonal boron nitride, for which we map the ex-ph relaxation times as a function of exciton momentum and energy, analyze the temperature and phonon-mode dependence of the ex-ph scattering processes, and accurately predict the phonon-assisted photoluminescence. The approach introduced in this work is general and provides a framework for investigating exciton dynamics in a wide range of materials.

Temperature-dependent Spectral Emission of Hexagonal Boron Nitride Quantum Emitters on Conductive and Dielectric Substrates

“…In a regime where the phonon energy is small compared to kT, a linear dependence of linewidth on temperature can be expected. A recent study [50] on exciton-phonon interaction in h-BN shows a similar linear trend in the exciton-phonon scattering rate in h-BN.…”

The role of chalcogen vacancies for atomic defect emission in MoS2

“…If further relaxation of the captured exciton into an excitonic state of type D 1 is slow or prohibited, the emission will occur dominantly from the fully localized electron and hole state. From a theory point of view, the above picture demands not only going from absorption to emission, but also to include further interactions, such as exciton-exciton or exciton-phonon coupling 47 . The latter is motivated by the fact that previous work described the asymmetric line shape of defect emission by an independent boson model with a phonon bath 27 .…”

Excitons under strain: light absorption and emission in strained hexagonal boron nitride

“…But experiments and theory are still qualitatively far, the reduction of the S3/S1 ratio we found is too small compared with measurements. This could be attributed to the lack of a fine sampling for the exciton and phonon dispersions [29], that is not possible with a finite difference approach or to the presence of surface effects [25] not included in the present calculations. Finally for larger compression the energy differences between the different indirect excitons become larger and larger and only the lowest exciton contributes to the spectra while the higher energy peaks are suppressed by the Boltzmann factor in Eq.…”

“…Luminescence in indirect materials can be studied by taking into account atomic vibrations that couple with indirect excitons. For h-BN this has been recently done by means of finite difference approaches [4,23] and by direct calculation of the exciton-phonon matrix elements [29]. The exciton-phonon matrix elements correspond to the derivatives of the excitonic dipole matrix elements with respect to the phonon modes [4].…”