Orbital and spin current density backflow in unidirectional monochromatic electromagnetic fields in vacuum

TL;DR

This paper investigates energy backflow and spin current backflow in unidirectional monochromatic electromagnetic fields, revealing unexpectedly strong spin current backflow and analyzing its relation to local wave properties.

Contribution

It provides a detailed analysis of energy and spin current backflow in 2D monochromatic electromagnetic waves, including electric and magnetic contributions, across different polarization states.

Findings

Spin current backflow is unexpectedly strong.

Energy backflow correlates with local wavenumbers and vortices.

Study includes scalar and vector wave versions.

Abstract

In this study, energy backflow in the Poynting vector, as well as its orbital and spin current density components, has been examined for a 2-dimensional causal unidirectional vector-valued monochromatic electromagnetic wave. Linear transverse electric (TE), transverse magnetic (TM), and circular polarization cases are considered and studied in detail, including both electric and magnetic contributions to the current density components. Spin current backflow has been found to be unexpectedly strong. A study of the energy backflow is also presented in the scalar version of the 2-dimensional monochromatic wave. A detailed study has been carried out of the correlation of the positions of energy backflows with local wavenumbers and their signs, the zeros of appropriate intensities and the presence of vortices.