jz0c00183_si_001.pdf (210.48 kB)
Anharmonicity Explains Temperature Renormalization Effects of the Band Gap in SrTiO3
journal contribution
posted on 2020-03-17, 02:29 authored by Yu-Ning Wu, Wissam A. Saidi, Jeffrey K. Wuenschell, Terumasa Tadano, Paul Ohodnicki, Benjamin Chorpening, Yuhua DuanSoft
phonon modes in strongly anharmonic crystals are often neglected
in calculations of phonon-related properties. Herein, we experimentally
measure the temperature effects on the band gap of cubic SrTiO3, and compare with first-principles calculations by accounting
for electron–phonon coupling using harmonic and anharmonic
phonon modes. The harmonic phonon modes show an increase in the band
gap with temperature using either Allen–Heine–Cardona
theory or finite-displacement approach, and with semilocal or hybrid
exchange-correlation functionals. This finding is in contrast with
experimental results that show a decrease in the band gap with temperature.
We show that the disagreement can be rectified by using anharmonic
phonon modes that modify the contributions not only from the significantly
corrected soft modes, but also from the modes that show little correction
in frequencies. Our results confirm the importance of soft-phonon
modes that are often neglected in the computation of phonon-related
properties and particularly in electron–phonon coupling.