First-Principles Calculations of Magnetotransport and Electron-Phonon Interactions in Semiconductors and Topological Materials

Understanding and predicting electron transport in novel materials is crucial to develop practical applications and accelerate materials discovery. Electron-phonon (e-ph) interactions are a key source of electron scattering and therefore play a dominant role in limiting electron transport under applied external fields. These interactions and the resulting phonon-limited charge transport can be calculated very accurately using ab-initio methods based on the semiclassical Boltzmann transport equation (BTE), where electron and phonon properties are obtained using density functional theory (DFT) and density functional perturbation theory (DFPT) techniques. Despite these advances, first-principles calculations of magnetotransport are still in their infancy, primarily due to technical challenges associated with solving the BTE in the presence of a magnetic field. Additionally, calculations of electrical charge transport and magnetotransport in topological materials are lacking because of various technical challenges, including computational cost and the absence of a unified formalism combining electron scattering and band topology in the BTE. In this work, we develop a framework that incorporates these effects into the BTE to compute charge transport, magnetotransport and topological transport regimes in several classes of conventional and quantum materials. Our magnetotransport calculations achieve excellent agreement with experiments, and we uncover an interplay of strong e-ph interactions and magnetic fields in graphene through a microsopic analysis of steady-state electron distributions. As a first step toward including band topology, we compute e-ph interactions and charge transport in the Dirac semimetal Na₃Bi and find that specific two-dimensional phonons control charge transport near room temperature. These lattice vibrations induce a dynamic phase transition to a Weyl semimetal, providing a platform for ultrafast control of dynamical phases in Na₃Bi. Expanding into more advanced phenomena, we incorporate the electron Berry curvature in the BTE formalism and study topological transport effects such as the chiral anomaly and nonlinear Hall effect (NLHE). Our calculations provide an accurate quantitative framework and demonstrate the importance of e-ph interactions in accurately describing topological transport in quantum materials. Lastly, we compute e-ph interactions in a novel correlated metal, RuO₂ which has been widely studied for its unconventional magnetism. We uncover various interesting properties such as phonon softening, strong e-ph band renormalization and a high superconducting Tc upon application of strain in RuO₂. Finally, we show a method to significantly accelerate all these calculations by compressing the matrices representing e-ph interactions. In summary, this work expands the scope of first-principles transport calculations to include magnetic fields and band topology. This enables future studies of electron dynamics in broad classes of novel quantum materials.