Berlin 2018 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 14: Frontiers of Electronic-Structure Theory: Correlated Electron Materials I (joint session O/MM/DS/TT/CPP)

TT 14.10: Vortrag

Montag, 12. März 2018, 12:45–13:00, HL 001

Small-Polaron Formation in Polymorphs of Ga₂O₃ and TiO₂ — •Sebastian Kokott, Sergey V. Levchenko, and Matthias Scheffler — Fritz-Haber-Institut der MPG, Berlin 14195, Germany

Transparent oxides are key materials for new devices in photovoltaics and electronics. One important factor influencing the behavior of charge carriers in these materials is the interaction with polar phonon modes. We focus on materials with strong electron-phonon coupling, where small polarons are formed. Although, density-functional theory (DFT) is often used for calculating polaron properties, there are two challenges: Sensitivity of the calculated properties to the errors in exchange-correlation treatment, and finite-size effects in supercell calculations. We have developed an approach [1] to address these issues. The polaron properties are obtained using a modified neutral potential-energy surface from DFT [2]. Based on Pekar^′s model [3], we correct for the proper elastic long-range behavior of the polaron in a supercell. With this approach, the influence of the crystal structure on the polaron properties is investigated for rutile and anatase TiO₂, and for the monoclinic β– and orthorhombic ε–Ga₂O₃. We find that in rutile TiO₂ only small electron polarons are stable, while only small hole polarons are found in anatase. On the contrary, small hole polarons exist in both Ga₂O₃ polymorphs but have significantly different binding energies.

[1] S. Kokott, arXiv:1710.03722 (2017)

[2] B. Sadigh et al., Phys. Rev. B 92, 75202 (2015)

[3] S. I. Pekar, Zh. Eksp. Teor. Fiz. 16 335 (1946)