Deliverable D3.1 : Report on ab-initio modelling for spin-based THz emitters

Work package 3 : Theoretical Fundamentals (TF)

Date: January 31, 2020

Abstract:

In this deliverable, we report on:

(1)  ab initio calculations that have been performed to obtain accurate values of the decisive materials’ quantities in spin-to-charge conversion processes. The responsible quantities are the spin Hall effect (SHE) and the spin Rashba-Edelstein effect (SREE), that convert electric current to spin current and spin accumulation. The inverse of these quantities plays a role in the spin-current driven THz emission. Specifically, we investigate from first-principles the SHE and SREE for thin Pt/3d-metal bilayers, such as Pt/Ni and Pt/Co, as well as, for comparison, Pt/Cu and Pt/Pt (without symmetrybreaking at the interface). We furthermore report investigations for the orbital Hall effect (OHE) and the orbital Rashba-Edelstein effect (OREE) that convert charge current in an orbital current and an orbital polarization. The influence of these orbital components on THz emission is as yet unknown. Our atom-resolved calculations determine which of
the effects is largest at the interface and how they contribute to the spin-orbit torque (SOT) acting on the magnetization of the 3d layer. (UU)

(2)   We further study current-induced generation of spin and orbital polarization in the symmetry-broken antiferromagnets (AFM) CuMnAs and Mn2Au, in the full frequency range. We find that the OREE gives the largest contribution in these materials. (UU)

(3) Ab initio calculations have furthermore been performed to compute the spin transparency at the Co/Pt interface. These spin transparencies have been employed to develop a simplified model to predict the THz emission from Co/Pt bilayers that can be compared with the more elaborate superdiffusion model. (CNRS-UMPhy, UU) (4) Lastly, we report on the electronic properties of bilayer systems that contain layers
of Bi or BiSb to study the interfacial Rashba effect and the influence of topological interfaces on spin-charge conversion in Co/BiSb bilayers. (CNRS-UMPhy, VSB)