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Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Santa Cruz Electronic Theses and Dissertations (2024)

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.

    Cover page: Excited-State Dynamics in Solid-State Spin Defects and Spin Dynamics of Carriers in Solids from First-PrinciplesCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2024)
    Spintronics in halide perovskites has drawn significant attention in recent years, due to their highly tunable spin-orbit fields and intriguing interplay with lattice symmetry. Here, we perform first-principles calculations to determine the spin relaxation time (T1) and ensemble spin dephasing time ([Formula: see text]) in a prototype halide perovskite, CsPbBr3. To accurately capture spin dephasing in external magnetic fields we determine the Landé g-factor from first principles and take it into account in our calculations. These allow us to predict intrinsic spin lifetimes as an upper bound for experiments, identify the dominant spin relaxation pathways, and evaluate the dependence on temperature, external fields, carrier density, and impurities. We find that the Fröhlich interaction that dominates carrier relaxation contributes negligibly to spin relaxation, consistent with the spin-conserving nature of this interaction. Our theoretical approach may lead to new strategies to optimize spin and carrier transport properties.
      Cover page: How spin relaxes and dephases in bulk halide perovskites.
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2023)
      Magnetic materials with noncollinear spin textures are promising for spintronic applications. To realize practical devices, control over the length and energy scales of such spin textures is imperative. The chiral helimagnets Cr1/3NbS2 and Cr1/3TaS2 exhibit analogous magnetic-phase diagrams with different real-space periodicities and field dependence, positioning them as model systems for studying the relative strengths of the microscopic mechanisms giving rise to exotic spin textures. Although the electronic structure of the Nb analogue has been experimentally investigated, the Ta analogue has received far less attention. Here, we present a comprehensive suite of electronic structure studies on both Cr1/3NbS2 and Cr1/3TaS2 using angle-resolved photoemission spectroscopy and density functional theory. We show that bands in Cr1/3TaS2 are more dispersive than their counterparts in Cr1/3NbS2, resulting in markedly different Fermi wavevectors. The fact that their qualitative magnetic phase diagrams are nevertheless identical shows that hybridization between the intercalant and host lattice mediates the magnetic exchange interactions in both of these materials. We ultimately find that ferromagnetic coupling is stronger in Cr1/3TaS2, but larger spin-orbit coupling (and a stronger Dzyaloshinskii-Moriya interaction) from the heavier host lattice ultimately gives rise to shorter spin textures.
        Cover page: Comparative Electronic Structures of the Chiral Helimagnets Cr1/3NbS2 and Cr1/3TaS2
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