UC Santa Cruz

The spin degree of freedom can be controlled in systems of solid-state spin defects or via the spin of carriers in solids.To achieve effective control, it requires in-depth understanding of the excited-state dynamics in spin defects, and the mechanisms by which carrier spin relaxes and dephases in solids. This thesis presents the development and application of advanced first-principles methods that accurately describe the electronic structures and interaction processes, providing a comprehensive understanding of excited-state dynamics.

For the solid-state spin defects, the challenges include identifying the chemical structure of spin defects and predicting their spin-dependent photoluminescence (PL) contrast. Regarding the defect identification, we use the density functional theory (DFT) and many-body perturbation theory to calculate a complete set of static and dynamical properties of spin defects, including exciton-defect coupling and electronphonon coupling. We demonstrate that certain spin defects candidates that can explain experimental observations. For predicting the spin-dependent PL contrast, we develop and implement the first-principles optically-detected magnetic resonance (ODMR). We show the prediction of spin-orbit coupling (SOC) and intersystem-crossing (ISC) with multi-reference electronic states. With this first-principles tool and accurate description of the excited-state dynamics, we achieve accurate prediction of the ODMR of spin defects.

For the spin of carriers in solids, understanding the mechanisms of spin dynamics and the intrinsic properties of solids requires accurate simulation of spin lifetimes (τs) for spin relaxation and dephasing. We utilize our developed first-principles real-time density-matrix (FPDM) approach to simulate spin dynamics in general solid-state systems. This approach provides a complete first-principles description of light–matter interactions and scattering processes, including electron–phonon, electron–impurity, and electron–electron scatterings with self-consistent spin-orbit coupling. By employing thismethod, we successfully reproduce experimental results for spin relaxation lifetime (T1) and spin dephasing time (T∗2 ). Our findings demonstrate that the Frohlich interaction, which primarily governs carrier relaxation, has minimal impact on spin relaxation. We also show that the dynamical Rashba effect results in anisotropy of spin lifetime and provide insights into how symmetry affects spin relaxation and transport.