Total angular momentum dichroism of the terahertz vortex beams at the antiferromagnetic resonances

TL;DR

This study demonstrates that terahertz vortex beams exhibit strong dichroism at antiferromagnetic resonances, with the effect governed by the total angular momentum, revealing new selection rules beyond conventional circular dichroism.

Contribution

The paper introduces the concept of total angular momentum dictating selection rules in AFM resonances using terahertz vortex beams, a novel approach in magnetic resonance studies.

Findings

Strong vortex beam dichroism observed at AFM resonances.

Dichroism magnitude comparable to circular dichroism.

Selection rules governed by total angular momentum j = σ + l.

Abstract

Terahertz vortex beams with different superposition of the orbital angular momentum $l={\pm}1$, ${\pm}2$, ${\pm}3$, and ${\pm}4$ and spin angular momentum ${\sigma}={\pm}1$ were used to study antiferromagnetic (AFM) resonances in TbFe$_3$(BO$_3$)$_4$ and Ni$_3$TeO$_6$ single crystals. In both materials we observed a strong vortex beam dichroism for the AFM resonances that are split in external magnetic field. The magnitude of the vortex dichroism is comparable to that for conventional circular dichroism due to ${\sigma}$. The selection rules at the AFM resonances are governed by the total angular momentum of the vortex beam: $j={\sigma}+l$. In particular, for $l={\pm}2$, ${\pm}3$, and ${\pm}4$ the sign of $l$ is shown to dominate over that for conventional circular polarization ${\sigma}$.