Converting Non-Equilibrium Charge Density into Spin Current
The interconversion between charge and spin degrees of freedom is of both fundamental and technological relevance in spintronics. While a non-equilibrium spin density and a charge current are related by the well-known Rashba-Edelstein effect, here I will show our recent results reporting on the generation of a time-dependent spin current due to a periodic modulation of the charge density. By using the Boltzmann transport equation, we show that when the chemical potential is varied, a spin current is generated in the time scale it takes for the system to re-equilibrate in the new chemical potential. The effect is ubiquitous in many systems with spin-momentum locking, and we propose a simple device scheme to measure the spin accumulation resulting from such time-dependent spin current. Our findings show novel fundamental insights between charge-to-spin conversion mechanisms and put forward an all-electrical way to generate spin currents without the need for charge currents, magnetic materials or optical methods.
Marc Vila Tusell is a postdoc at the Lawrence Berkeley National Laboratory and the department of physics of the University of California, Berkeley, working with Professor Joel Moore. He completed his bachelor in Nanoscience and Nanotechnology from the Autonomous University of Barcelona and obtained his Ph.D. in theoretical physics from the same university in 2020. His Ph.D. research, carried out at the Catalan Institute of Nanoscience and Nanotechnology, focused on the theoretical exploration of spin transport in two-dimensional quantum materials such as graphene, transition metal dichalcogenides and topological insulators. Currently, he is interested in transport properties of magnetic materials and spin-orbitronics, i.e. the usage of spin-orbit coupling to envision spintronic applications and topological states of matter.
Curvature-Induced Radial and Lateral Heterogeneity of Grafted Polymers
Polymer grafted nanoparticles (PGNPs) have gained prominence as building blocks to generate functional single-component composites (SCCs), as they can offer high inorganic loadings with polymeric processability. Understanding the phase behavior of grafted polymers on a single chain level has been proven essential to engineer surface modifications and PGNP-based SCCs. As the nanoparticle size increases beyond a few to tens of nanometers, the surface curvature reduces substantially. We hypothesize that the increased local flatness will affect the lateral organization of the grafted polymer chains to form pseudo-faceted nanoparticles. Here we tested the hypothesis in the regime where the ratio of particle diameter to polymer radius of gyration in the range of ten to hundred, d/Rg = 10–100, and experimentally demonstrated that d/Rg has a direct impact on PGNP assembly and how the resultant assemblies dissipate external stresses. Nanoindentation experiments on thin film and bulk PGNP composites demonstrated that in addition to composition, the polymer chain arrangements between PGNPs also have an effect on the mechanical properties. Single particle indentation also revealed different stages of energy dissipation associated with chain conformation and organization. The deformation behavior of PGNP film indicated an anisotropic orientation of the grafted polymers, a deviation from previously reported d/Rg ≈ 1 systems. Present studies clearly showed the need to explore PGNP-based SCCs with particle size in the hundreds of nanometers where new and emergent phenomena may arise when local chain arrangements in both radial and lateral directions are taken into consideration. This introduces a novel framework to engineer functional PGNP-based SCCs.
Tiffany Chen is a 5th-year Chemistry Ph.D. student in Ting Xu's group studying the self-assembly of polymer grafted nanoparticles and their properties. She obtained her B.S. in Chemistry at UC San Diego in 2017, where she worked for Michael Sailor on surface modification of porous silicon nanomaterials. In her free time, she enjoys puzzles, arts and crafts, and baking.