The study investigates the absorption and emission of chiral light using arrays of graphene nanodisks.
A photonic structure is considered chiral if it cannot be superimposed on its mirror image through translations and rotations. Chiral photonic structures respond differently to left- and right-handed circularly polarized light components, a phenomenon known as circular dichroism. This capability makes these structures ideal tools for detecting and manipulating chiral molecules, which is essential in biotechnology. Furthermore, chiral photonic structures can modify the polarization state of light and generate circularly polarized thermal radiation. This has driven the research and development of various chiral photonic elements, such as emitters, cavities, metasurfaces, and collective modes in periodic systems. An alternative strategy to achieve circular dichroism is the use of materials with a strong magneto-optical response. Graphene, a single layer of carbon atoms, stands out as a promising platform due to its exceptional optical and electronic properties. When a static magnetic field is applied perpendicular to a graphene layer, its optical conductivity acquires off-diagonal Hall components, resulting in an extraordinary magneto-optical response. Additionally, when doped with charge carriers, graphene nanostructures can support localized plasmonic modes, which strongly enhance light-matter interaction in the terahertz and infrared spectral ranges. Thus, when doped and subjected to a magnetic field, graphene nanostructures support magnetoplasmons that enable chiral light-matter interactions. Moreover, their two-dimensional structure and low electronic heat capacity allow strong variations in the optical response with temperature, presenting new opportunities to control and manipulate these plasmons. In this theoretical study, we have investigated how to thermally control the absorption and emission of chiral light using graphene magnetoplasmons. We have found that, at finite temperature and with a static perpendicular magnetic field, the magnetoplasmons of arrays of graphene disks strongly hybridize with transitions between Landau levels, forming thermal hybrid magnetoplasmons (TMPs). These TMPs, when combined with a gold mirror in a Salisbury screen configuration, enable perfect chiral absorption (perfect absorption for only one polarization of light). Additionally, this system generates completely circularly polarized thermal radiation in a single direction, extending graphene's known capability to mediate thermal emission and paving the way for nonreciprocal thermal emitters, thereby advancing solar energy harvesting technologies.
