Magnetic Skyrmions and Topological Insulators for Spintronics Applications

To increase the memory storage and processing capabilities of computers, the density of transistors need to be scaled up. One of the main bottlenecks of increasing the density is the heat generation and energy consumption of the devices, which limit how small we can go. One alternative is to use spins instead of electrons to process and store information. The field of using spins for computing is known as spintronics. However, there are challenges in generating spin current and high density spintronics devices. Topological phases of matter offer exciting properties that can be used in spintronics and address some of the challenges.

We develop and use a range of tools to cover the analysis of the devices going from material level to transport and dynamics to circuit level analysis. At the material level we use ab-initio results as an input for Non Equilibrium Green Function (NEGF) formalism and Landau Lifshitz Gilbert (LLG) equation to study quantum transport and magnetodynamics, which in turn act as an input for circuit level analysis.

Using LLG, we study the magnetic skyrmions, which are topological quasiparticles in magnetic moment space. We propose and investigate the underlying physics of a type of self-focusing skyrmions and their possible applications as reconfigurable logic units. Also, we propose an unconventional application for skyrmion for temporal computing using the dynamical properties of skyrmions. We design and study the control circuit and its energy consumption, going all the way from LLG calculations to circuit simulation and compact modeling. In addition, to control and tune the motions of skyrmions, we develop a numerical tool based on mathematical models to investigate the positional lifetime of skyrmions in the presence of notches and imperfections of their host material.
We turn to topological insulators (TI) as an option to generate spin current. We use tight binding models fitted to ab-initio calculations from literature as our toy model and use it in the NEGF formalism to simulate the quantum transport of TI channels. Finally, we study FM/TI heterostrucres and propose a device based on their reciprocal interaction. We solve NEGF-LLG equations self consistently and combine it with Fokker-Planck equations to estimate the device performance.