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

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.

Dzyaloshinskii-Moriya interaction induced by an ultrashort electromagnetic pulse: Application to coherent (anti)ferromagnetic skyrmion nucleation

“…The s electrons are assumed to be at the origin of itinerant magnetism, whereas the p − d electrons are localized around their nuclei to form ionic spins that are responsible for localized magnetism. We assume that the delocalized electrons can be modeled by a 2DEG (ultrathin film geometry), and the light-matter interaction is described by a semirelativistic expansion of the Dirac-Maxwell mean-field model [32]. As detailed in the Supplemental Material (SM) [33], and in Ref.…”

“…As detailed in the Supplemental Material (SM) [33], and in Ref. 32, at the lowest order in powers of 1/c, the spin-light interaction Hamiltonian reads,…”

Study Zitterbewegung effect in a quasi one-dimensional relativistic quantum plasma by Dirac-Heisenberg-Wigner formalization

“…in which the coefficients f 's, with f 0 and f 3 as scalars and f 1 and f 2 as pseudoscalares, and g's, with g 1 and g 2 as vectors and g 0 and g 3 as pseudovectors, are dimensionless functions of r, v, and t. All DHW functions are real over the phase space and some of them have clear physical meaning [44] The full set of equations for the 16 components of the DHW function describing the Dirac field is as follows [47] ∂f…”

“…We assume the system is imbedded in a neutralizing background of positive charge. To the best of our knowledge, no deliberation has been made of the ZB effect in quantum relativistic plasma using the combination of Dirac wave functions and the Wigner operator, although a quantum kinetic theory taking spin-orbit coupling and ZB into account for the collective motion of electrons [43] as well as a plasma model including the Darwin term (associated with ZB) [44] were analyzed. Gauge-invariant 2 × 2 Wigner matrix on the basis of the Hamiltonian form of the Klein-Gordon equation and non-Gaussian Dirac spinors with positive relativistic…”

Signatures of relativistic spin-light coupling in magneto-optical pump-probe experiments

“…Notably, at such short time delay there is a non-negligible overlap of the pump and probe beams, suggesting that the interaction of these beams plays a role. The coherent contrib ution to the magnetization dynamics was attributed to relativistic quantum electrodynamics stemming from relativistic effects beyond the common crystalline spin-orbit interaction [45,47,48]. It is already well established that the magnetooptical Kerr effect is a relativistic quantum effect because of its relation to the crystalline spin-orbit coupling [8,49,50].…”