We will perform a computational study of real-time charge and spin dynamics in realistic microscopic models of transition metal dichalcogenides (TMDC) on metal substrates and of TMDC/metal heterostructures. Thereby we will unveil the interplay between strain, spin-orbit coupling, and an applied time-dependent field or bias. We plan to go beyond the simple geometries where a uniform strain is applied to the TMDC, and allow for more complex systems with a non-uniform strain field, resulting in uniform or space-modulated pseudo-magnetic fields. One of our major objectives is to find a strategy to control the valley depolarization time. There are a series of control “knobs” that we can use. The obvious one is the temperature, but we can also use other external parameters such as strain (one-dimensional, two-dimensional, or non-uniform) or the interaction of the TMDC with the substrate. In fact, the coupling to the metallic substrate (magnetic or non-magnetic) may allow us to engineer the magnetization, spin-orbit coupling and electron-phonon interactions within the TMDC layer. Another important question we will address is the possibility to inject charge and spin currents from/to the TMDC.
Our main tools will be both time-dependent density functional theory (TDDFT) and time-dependent density functional tight-binding theory (TD-DFTB). The first approach will be mainly used to benchmark small systems. The TD-DFTB tool, whose development is a major part of the project, will allow us to study large systems containing thousands of atoms (a few nm in the parallel directions) over very long time-scales (on the order of ps), thereby providing access to the interplay between electron relaxation and transport, as well as to magnon and phonon dynamics.
Propagators for the time-dependent Kohn–Sham equations: Multistep, Runge–Kutta, exponential Runge–Kutta, and commutator free Magnus methods
A. Gómez Pueyo, M. A. L. Marques, A. Rubio, and A. Castro
J. Chem. Theory Comput. 14, 3040 (2018) - DOI: 10.1021/acs.jctc.8b00197