Frontiers in Physics (Aug 2023)
Manipulation of magnetization and spin transport in hydrogenated graphene with THz pulses
Abstract
Terahertz (THz) field pulses can now be applied in scanning tunneling microscopy (THz-STM) junction experiments to study time-resolved dynamics. The relatively slow pulse compared to the typical electronic time-scale calls for approximations based on a time-scale separation. Here, we contrast three methods based on non-equilibrium Green’s functions: i) the steady-state, adiabatic results, ii) the lowest-order dynamic expansion in the time variation, and iii) the auxiliary mode propagation method without approximations in the time variation. We consider a concrete THz-STM junction setup involving a hydrogen adsorbate on graphene where the localized spin polarization can be manipulated on/off by a local field from the tip electrode and/or a back-gate affecting the in-plane transport. We use steady-state non-equilibrium Green’s function theory combined with density functional theory to obtain a Hubbard model for the study of the junction dynamics. Solving the Hubbard model in a mean-field approximation, we find that the near-adiabatic first-order dynamic expansion in the time variation provides a good description for STM voltage pulses up to the 1 V range.
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