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arXiv · 1612.05679

Polaron-induced phonon localization and stiffening in rutile TiO$_2$

Grigory Kolesov·Boris A. Kolesov·Efthimios Kaxiras
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Abstract

Small polaron formation in transition metal oxides, like the prototypical material rutile TiO$_2$, remains a puzzle and a challenge to simple theoretical treatment. In our combined experimental and theoretical study, we examine this problem using Raman spectroscopy of photo-excited samples and real-time time-dependent density functional theory (RT-TDDFT), which employs Ehrenfest dynamics to couple the electronic and ionic subsystems. We observe experimentally the unexpected stiffening of the $A_{1g}$ phonon mode under UV illumination and provide a theoretical explanation for this effect. Our analysis also reveals a possible reason for the observed anomalous temperature-dependence of the Hall mobility. Small polaron formation in rutile TiO$_2$ is a strongly non-adiabatic process and is adequately described by Ehrenfest dynamics at time scales of polaron formation.

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Grigory Kolesov, Boris A. Kolesov, Efthimios Kaxiras. 2017-09-01. Polaron-induced phonon localization and stiffening in rutile TiO$_2$. https://doi.org/10.1103/physrevb.96.195165

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