First-principles modeling of spin-mixing in organic semiconductors

Abstract

Research in organic semiconductors for spintronic applications was initiated roughly two decades ago. In recent years, there have been several studies that investigate the spin-relaxation and transport phenomena based on the understandings prevalent for solid state materials. Spin-mixing in opposite spin states due to the spin-orbit coupling (SOC) has been identified as one of the major driving factors for spin-relaxation. The degree of spin-mixing in organics can be easily calculated from theoretical techniques and assist predictions of essential spintronic phenomena. However, most of the work in literature use crude analytical techniques or semi-empirical approximations. The aim of this thesis is to introduce a first-principle approach that enable a better understanding of spin-relaxation in organics using the spin-admixture parameter ($\gamma$). We present a generalized formalism, void of any parameters and demonstrate its accuracy and transferability across different classes of organic compounds relevant for spintronics, including molecular magnets. This approach is easy to implement for high-throughput computational stu- dies and its predictive accuracy has been benchmarked against experiments. The results also emphasize the complementarity of the approach to the experiments as $\gamma$ can be used a theoretical design tool to tune the SOC in molecules.