Elucidating the details of the electron-phonon coupling in semiconductors and insulators is a topic of pivotal interest, as it governs the transport mechanisms and is responsible for various phenomena such as spectral-weight transfers to phonon sidebands and self-trapping. Here, we investigate the influence of the electron-phonon interaction on the excitonic peaks of rutile TiO2, revealing a strong anisotropic polarization dependence with increasing temperature, namely an anomalous blueshift for light polarized along the a-axis and a conventional redshift for light polarized along the c-axis. By employing many-body perturbation theory, we identify two terms in the electron-phonon interaction Hamiltonian that contribute to the anomalous blueshift of the a-axis exciton. Our approach paves the way to a complete ab initio treatment of the electron-phonon interaction and of its influence on the optical spectra of polar materials.
@article{arxiv.1704.00176,
title = {Anomalous Anisotropic Exciton Temperature Dependence in Rutile TiO2},
author = {Edoardo Baldini and Adriel Dominguez and Letizia Chiodo and Evgeniia Sheveleva and Meghdad Yazdi-Rizi and Christian Bernhard and Angel Rubio and Majed Chergui},
journal= {arXiv preprint arXiv:1704.00176},
year = {2017}
}