Plasmonic Vortices Host Magnetoelectric Interactions

TL;DR

This paper demonstrates imaging of dot(E,H) fields in plasmonic vortex cores at nanometer scales, revealing enhanced magnetoelectric interactions relevant for axion-like quasiparticles and ultrafast magnetoelectric phenomena.

Contribution

It introduces a method to image and analyze the magnetoelectric dot(E,H) fields in plasmonic vortices at subwavelength scales using ultrafast photoemission electron microscopy, revealing new symmetry properties.

Findings

Dot(E,H) fields are intensified in plasmonic vortex cores at ~10 nm scale.

Magnetoelectric symmetry class with broken parity and time reversal is identified.

Imaging enables ultrafast microscopy of magnetoelectric responses in materials.

Abstract

The vector cross product and pseudoscalar dot products of electric (E) and magnetic (H) fields are separately finite in vacuum transverse electric and magnetic (TEM) plane waves, and angular momentum structured light. Current theories of interactions beyond the standard model of particle physics invoke non-zero dot(E,H) as the source term in the axion law that describes interactions with the cosmological dark matter axion particles outside of the quartet of Maxwells equations. The non-zero dot(E,H) also drives relativistic spin-charge magnetoelectric excitations of axion quasiparticles at a distinctively higher condensed matter scale in magnetic and topological materials. Yet, how to drive coherent dot(E,H) responses is unknown, and provides motivation to examine the field polarizations in structured light on a deep sub-diffraction limited spatial scale and sub-optical cycle temporal scale by ultrafast nonlinear photoemission electron microscopy. By analytical theory and ultrafast coherent photoemission electron microscopy, we image dot(E,H) fields in surface plasmon polariton vortex cores at subwavelength scales, where we find that the magnetoelectric relative to the dipole density is intensified on a ~10 nm diameter scale as a universal property of plasmonic vortex fields. The generation and nanoscale localization of dot(E,H) fields introduces the magnetoelectric symmetry class, having the parity and time reversal broken, but the joint parity-time reversal symmetry preserved. The ability to image the optical fields of plasmonic vortex cores opens the research of ultrafast microscopy of magnetoelectric responses and interactions with axion quasiparticles in solid state materials.