Anomalous Anisotropic Exciton Temperature Dependence in Rutile TiO2

Physical Review B 96 , 041204(R) (2017)

Anomalous Anisotropic Exciton Temperature Dependence in Rutile TiO2

Edoardo Baldini,Adriel Dominguez,Letizia Chiodo,Evgeniia Sheveleva,Meghdad Yazdi-Rizi,Christian Bernhard,Angel Rubio, Majed Chergui

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 TiO$_2$, 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.

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We thank Ingalena Bucher for her contribution during the measurements. We acknowledge nancial support from the Swiss NSF via the NCCR:MUST and the contracts No. 206021 157773, 20020 153660 and 407040 154056 (PNR 70), the European Research Council Advanced Grants H2020 ERCEA 695197 DYNAMOX and QSpec-NewMat (ERC-2015-AdG-694097), Spanish Grant FIS2013- 46159-C3-1-P, Grupos Consolidados del Gobierno Vasco (IT578-13), COST Actions CM1204 (XLIC), MP1306 (EUSpec) and European Unions H2020 program under GA no.676580 (NOMAD).

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