Dynamics of the Chirality Induced Spin Selectivity Effect under Non-Equilibrium

Sammanfattning

Over the past two decades, chirality induced spin selectivity (CISS) has emerged as its own field of research. As a phenomenon, it reveals how the shape of molecules interplay with electron dynamics, showcasing how a helical molecule acts as a filter for electron spins, and thus, provides valuable insights into the correlation between molecular structure and electron properties. The interpretation is that the influence of the helical molecular structure, along with spin-orbit interaction and non-equilibrium conditions causes the charge-carrying electrons to become spin-polarized. Consequently, the structure of these molecules effectively filters electrons based on their spin direction. In this project, we investigate the time evolution of the probability densities for each spin as well as the spin polarization in a simplified model of the helical molecule under non-equilibrium. The problem is treated both analytically for a simpler case and numerically for a more general one. In the more general case, the solutions are divided into two parts, namely 1) The unperturbed system, to determine the properties of the system, and 2) The perturbed system, to investigate consequences of different types of perturbations. Two types of sources of perturbation were considered, namely metals, both magnetic and non-magnetic, and external electric fields, where these are assumed both constant and time-dependent, such as harmonic or decaying. The results from the analytical and numerical models turned out to give essentially the same results, however a larger molecule than the very smallest was required to display the expected symmetry of spin polarization between helicities. The properties of the unperturbed system were consistent withprevious research, and the perturbations had a varying effect, with the magnetic metals producing distinct changes to the spin polarization while the electric field mostly shifted the total charge.