Controlling spin angular momentum and optical chirality via rotational plasmon modes

Circular dichroism (CD) signals in chiral and magneto-optical (MO) materials are governed by two distinct electromagnetic quantities: optical chirality (OC) and spin angular momentum (SAM), respectively. While OC and SAM are inseparable in free-space light, plasmonic nanostructures enable their decoupling in the near field. In this study, we demonstrate that rotational plasmon modes in nanodiscs and nanoholes allow for selective or simultaneous enhancement of OC and SAM. These enhancements result in distinct CD spectral features, whose shapes and signs depend on both the material response (absorptive vs. birefringent) and the field configuration. Our findings offer a framework for interpreting complex CD spectra and designing nanostructures with tailored light-matter interactions.