Coherent spin-light-induced mechanisms in the semi-relativistic limit of the self-consistent Dirac-Maxwell equations

TL;DR

This paper develops a semi-relativistic mean-field model based on the Dirac-Maxwell equations, revealing four spin-related mechanisms that influence coherent ultrafast spin dynamics under electromagnetic fields.

Contribution

It introduces an analytical semi-relativistic Hamiltonian derived from the Dirac-Maxwell equations, highlighting new spin mechanisms in light-matter interactions.

Findings

Identification of four spin-related mechanisms affecting ultrafast spin dynamics

Analytical expression for a light-induced mean-field Hamiltonian

Clarification of the roles of light-induced currents and charge densities

Abstract

We present a self-consistent mean-field model based on a two-component Pauli-like equation that incorporates quantum and relativistic effects (up to second-order in 1/c) for both external and internal electromagnetic fields. By taking the semi-relativistic limit of the Dirac-Maxwell equations in the presence of an external electromagnetic field we obtain an analytical expression of a coherent light-induced mean-field Hamiltonian. The latter exhibits several mechanisms that involve the internal mean fields created by all the electrons and the external electromagnetic field (laser). The role played by the light-induced current density and the light-induced second-order charge density acting as sources in Maxwell's equations are clarified. In particular, we identify clearly four different mechanisms involving the spins that may play an important role in coherent ultrafast spin dynamics.