Theory of spin Hall effect: extension of the Drude model

Nonlinear Optics-Driven Spin Reorientation in Ferromagnetic Materials

Based on nonlinear optics, we propose that light irradiation could induce a nonequilibrium steady state magnetization variation. We formulize a band theory to elucidate its general microscopic mechanisms, which are rooted by the quantum geometric structure and topological nature of electronic Bloch wave functions. The existence is determined by the light polarization and specific material symmetry, based on the magnetic group theory. In general, for a magnetic system, both circularly and linearly polarized light could exert an effective magnetic field and a magnetic "velocity" (magnetization variation rate over time, serving as an effective torque) to reorient the magnetization direction. They are contributed by spin and orbital angular momenta simultaneously. Aided by group theory and first-principles calculations, we illustrate this theory using a showcase example of monolayer NiCl2, showing that light irradiation effectively generates an out-of-plane effective magnetic torque, which lifts its in-plane easy magnetization. According to magnetic dynamic simulations, under light with a modest intensity, this switching could occur on the order of 0.1-1 ns time scale, demonstrating its ultrafast nature that is desirable for quantum manipulation.

Newton's second law in spin-orbit torque

Spin-orbit torque (SOT) refers to the excitation of magnetization dynamics via spin-orbit coupling (SOC) under the application of a charged current. In this work, we introduce a simple and intuitive description of the SOT in terms of spin force. In Rashba SOC system, the damping-like SOT can be expressed as [Formula: see text], in analogy to the classical torque-force relation, where R _c is the effective radius characterizing the Rashba splitting in the momentum space. As a consequence, the magnetic energy is transferred to the conduction electrons, which dissipates through Joule heating at a rate of [Formula: see text], with j _e being the applied current. Finally, we propose an experimental verification of our findings via measurement of the anisotropic magnetoresistance effect.

A Multithread Nested Neural Network Architecture to Model Surface Plasmon Polaritons Propagation

Surface Plasmon Polaritons are collective oscillations of electrons occurring at the interface between a metal and a dielectric. The propagation phenomena in plasmonic nanostructures is not fully understood and the interdependence between propagation and metal thickness requires further investigation. We propose an ad-hoc neural network topology assisting the study of the said propagation when several parameters, such as wavelengths, propagation length and metal thickness are considered. This approach is novel and can be considered a first attempt at fully automating such a numerical computation. For the proposed neural network topology, an advanced training procedure has been devised in order to shun the possibility of accumulating errors. The provided results can be useful, e.g., to improve the efficiency of photocells, for photon harvesting, and for improving the accuracy of models for solid state devices.