Electron Mobilities in SrTiO$_3$ and KTaO$_3$: Role of Phonon Anharmonicity, Mass Renormalization and Disorder

TL;DR

This study refines theoretical models to accurately predict electron mobility in SrTiO$_3$ and KTaO$_3$ by incorporating temperature-dependent phonon properties and disorder effects, aligning calculations with experimental data above 150 K.

Contribution

It introduces a method combining machine-learned force fields and anharmonic phonon calculations to improve mobility predictions in strongly anharmonic materials.

Findings

Calculated mobility for SrTiO$_3$ exceeds experimental values at room temperature.

Overestimation of mobility in KTaO$_3$ is less pronounced than in SrTiO$_3$.

Electron mass renormalization and disorder significantly affect mobility predictions.

Abstract

Accurately predicting carrier mobility in strongly anharmonic solids necessitates a precise characterization of lattice dyndamics as a function of temperature. We achieve consistency with experimental electron mobility data for bulk KTaO$_3$ and SrTiO$_3$ above 150 K by refining the Boltzmann transport equations. This refinement includes incorporating temperature-dependent anharmonic phonon eigenfrequencies and eigenmodes into the electron-phonon interaction tensor, while maintaining the derivatives of the Kohn-Sham potential as computed in density functional perturbation theory. Using efficient machine-learned force fields and the stochastic self-consistent harmonic approximation, we accurately compute the dynamical matrices. At room temperature, the calculated mobility for SrTiO$_3$ exceeds experimental values by an order of magnitude, whereas the overestimation for KTaO$_3$ is way less pronounced. This discrepancy is explained through the more significant electron mass renormalization near the conduction band bottom due to anharmonic electron-phonon coupling and the presence of local disorder in SrTiO$_3$.