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Microscopic theory of spin relaxation anisotropy in graphene with proximity-induced spin-orbit coupling
摘要： We present a microscopic theory of spin dynamics in weakly disordered graphene with uniform proximity-induced spin-orbit coupling (SOC). A time-dependent perturbative treatment is employed to derive the spin Bloch equations governing the spin dynamics at high electronic density for arbitrary ratio λSOC/η, where η is the disorder-induced quasiparticle broadening and λSOC is the largest spin-orbit energy scale. Rich scenarios are predicted, depending on a delicate competition between interface-induced Bychkov-Rashba and spin-valley interaction. In the motional narrowing regime of weak SOC (λSOC (cid:2) η), the anisotropy ratio of out-of-plane to in-plane spin lifetimes ζ = τ ⊥ s agrees qualitatively with a toy model of spins in a fluctuating SOC field proposed recently by Cummings and co-workers Phys. Rev. Lett. 119, 206601 (2017). For well-resolved SOC (λSOC (cid:2) η), the spin dynamics is characterized by fast damped oscillations with spins relaxing on the timescale of a single scattering event. In this regime, qualitatively different formulas for ζ are obtained, which can be useful to model spin transport in ultraclean van der Waals heterostructures.
关键词： spin-orbit coupling,van der Waals heterostructures,spin dynamics,Bychkov-Rashba,graphene,spin-valley interaction
更新于2025-09-04 15:30:14
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Spin–orbit coupling in silicon for electrons bound to donors
摘要： Spin–orbit coupling (SOC) is fundamental to a wide range of phenomena in condensed matter, spanning from a renormalisation of the free-electron g-factor, to the formation of topological insulators, and Majorana Fermions. SOC has also profound implications in spin-based quantum information, where it is known to limit spin lifetimes (T1) in the inversion asymmetric semiconductors such as GaAs. However, for electrons in silicon—and in particular those bound to phosphorus donor qubits—SOC is usually regarded weak, allowing for spin lifetimes of minutes in the bulk. Surprisingly, however, in a nanoelectronic device donor spin lifetimes have only reached values of seconds. Here, we reconcile this difference by demonstrating that electric ?eld induced SOC can dominate spin relaxation of donor-bound electrons. Eliminating this lifetime-limiting effect by careful alignment of an external vector magnetic ?eld in an atomically engineered device, allows us to reach the bulk-limit of spin-relaxation times. Given the unexpected strength of SOC in the technologically relevant silicon platform, we anticipate that our results will stimulate future theoretical and experimental investigation of phenomena that rely on strong magnetoelectric coupling of atomically con?ned spins.
关键词： silicon,spin relaxation,Spin–orbit coupling,donor-bound electrons,quantum information
更新于2025-09-04 15:30:14
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Can BODIPY Dimers Act as Photosensitizers in Photodynamic Therapy? A Theoretical Prediction
摘要： The photophysical properties of some monomeric and dimeric BODIPY systems were investigated at the density functional theory level and herein reported. In particular, the absorption spectra were fully characterized, low energy singlet and triplet excited states were discussed also focusing on the energy difference gaps between them and computing the spin-orbit couplings values for the possible intersystem crossing channels. The heavy atom effect of iodine substituents on the photophysical properties of a monomer and on a dimer under investigation was also estimated. Results obtained on the considered compounds allow us to predict which is the most promising candidate to be suggested as a photosensitizer in photodynamic therapy.
关键词： BODIPY,PDT,heavy atom effect,TDDFT,spin-orbit coupling
更新于2025-09-04 15:30:14
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Effects of spin-orbit coupling on the optical response of a material
摘要： We investigate the effects of spin-orbit coupling on the optical response of materials. In particular, we study the effects of the commutator between the spin-orbit coupling part of the potential and the position operator on the optical matrix elements using density functional theory calculations within the generalized gradient approximation. By means of a formalism that separates a fully relativistic Kleinman-Bylander pseudopotential into the scalar-relativistic and spin-orbit-coupling parts, we calculate the contribution of the commutator arising from spin-orbit coupling to the squared optical matrix elements of isolated atoms, monolayer transition-metal dichalcogenides, and topological insulators. In the case of isolated atoms from H (Z = 1) to Bi (Z = 83), the contribution of spin-orbit coupling to the squared matrix elements can be as large as 14%. On the other hand, in the cases of monolayer transition-metal dichalcogenides and topological insulators, we find that this contribution is less than 1% and that it is sufficient to calculate the optical matrix elements and subsequent physical quantities without considering the commutator arising from spin-orbit coupling.
关键词： optical response,spin-orbit coupling,transition-metal dichalcogenides,topological insulators,density functional theory
更新于2025-09-04 15:30:14
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Efficient and Long-lived Room Temperature Organic Phosphorescence: Theoretical Descriptors for Molecular Designs
摘要： Room-temperature phosphorescence (RTP) with long afterglow from pure organic materials has attracted great attentions for their potential applications in biological imaging, digital encryption and optoelectronic device and so on. Organic materials have been long considered to be non-phosphorescence owing to the weak molecular spin-orbit coupling and highly sensitive to temperature. However, recently, some purely organic compounds can demonstrate highly efficient RTP with long afterglow upon aggregation while others fail. Namely, it remains a challenge to expound the underline mechanisms. In this study, we present the molecular descriptors to character the phosphorescence efficiency and lifetime. For prototypical RTP system consists of carbonyl group and π-conjugated segments, the excited states can be regarded as admixture of n→π* (with portion α) and π→π* (portion β). Starting from phosphorescent process and El-Sayed rule, we deduced that (i) the intersystem crossing (ISC) rate of S1→Tn is mostly governed by the modification of the product of α and β, and (ii) the ISC rate of T1→S0 is determined by the β value of T1. Thus, the descriptors (γ=α×β, β) can be employed to describe the RTP character of organic molecules. From hybrid quantum mechanics and molecular mechanics (QM/MM) calculations, we illustrated the relationships amongst the descriptors (γ, β), phosphorescent efficiency and lifetime, as well as spin-orbit coupling constants. We stressed that the large γ and β values are favorable to the strong and long-lived RTP in organic materials. Experiments have reported confirmations of these molecular design rules.
关键词： Organic materials,Molecular descriptors,Room-temperature phosphorescence,QM/MM calculations,Spin-orbit coupling
更新于2025-09-04 15:30:14
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摘要： The spin-orbit coupling (SOC) interactions, electron-correlation effects, and Hund coupling cooperate and compete with each other, leading to novel properties, quantum phase, and nontrivial topological electronic behavior in iridium oxides. Because of the well-separated IrO6 octahedra approaching cubic crystal-field limit, the hexagonal iridates Sr3MIrO6 (M = Sr, Na, and Li) serve as canonical model systems to investigate the underlying physical properties that arise from the novel jeff state. Based on density-functional theory calculations complemented by Green’s function methods, we systematically explore the critical role of SOC on the electronic structure and magnetic properties of Sr3MIrO6. The crystal-field splitting combined with correlation effects are insufficient to account for the insulating nature, but the SOC interaction is the intrinsic source to trigger the insulating ground states in these hexagonal iridates. The decreasing geometry connectivity of IrO6 octahedra gives rise to the increase of effective electronic correlations and SOC interactions, tuning the hexagonal iridates from low-spin jeff = 1/2 states with large local magnetic moments for the Ir4+ (5d 5) ions in Sr4IrO6 to nonmagnetic singlet Jeff = 0 states without magnetic moments for the Ir5+ (5d 4) ions in Sr3NaIrO6 and Sr3LiIrO6. The theoretical calculated results are in good agreement with available experimental data, and explain the magnetic properties of Sr3MIrO6 well.
关键词： electronic structure,insulating state,magnetic properties,iridates,spin-orbit coupling
更新于2025-09-04 15:30:14
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Influence of Disorder and Anharmonic Fluctuations on the Dynamical Rashba Effect in Purely Inorganic Lead-Halide Perovskites
摘要： Doping organic metal-halide perovskites with cesium could be the best solution to stabilize highly-efficient perovskite solar cells. The understanding of the respective roles of the organic molecule, on one hand, and the inorganic lattice, on the other, is thus crucial in order to be able to optimize the physical properties of the mixed-cation structures. In particular, the study of the recombination mechanisms is thought to be one of the key challenges towards full comprehension of their working principles. Using molecular dynamics and frozen phonons, we evidence sub-picosecond anharmonic fluctuations in the fully inorganic CsPbI3 perovskite. We reveal the effect of these fluctuations, combined with spin-orbit coupling, on the electronic band structure, evidencing a dynamical Rashba effect. Our study shows that under certain conditions space disorder can quench the Rashba effect. As for time disorder, we evidence a dynamical Rashba effect which is similar to what was found for MAPbI3 and which is still sizable despite temperature disorder, the large investigated supercell, and the absence of the organic cations’ motion. We show that the spin texture associated to the Rashba splitting cannot be deemed responsible for a consistent reduction of recombination rates, although the spin mismatch between valence and conduction band increases with the ferroelectric distortion causing the Rashba splitting.
关键词： spin-orbit coupling,perovskite solar cells,Rashba effect,molecular dynamics,CsPbI3
更新于2025-09-04 15:30:14