The interaction between light and 2D materials spans from the ultra-violet spectrum all the way to microwaves. It involves a variety of different physical systems and quasi-particles, such as plasmons, excitons and phonons, which interact strongly with light. These light-matter interactions, can also occur in the form of polaritons, i.e. a quasi-particles that are composed from a photon and an excited state of matter (electron, phonon, exciton, etc). In the group we study the interaction between light and 2D materials, the physical and optical phenomena they inhabit, and their polaritonic nature. We utilize several experimental techniques to perform room-temperature and low-temperature electro-optical spectroscopy, from the visible to the far-infrared spectrum. We develop robust optical methods specifically adapted to 2D material and their atomic dimensions. Doing so allows us to study the extraordinary properties of 2D materials, to push nanophotonics into the atomic scale, and to build atomic-scale electronic and opto-electronic devices.
Plasmons in Graphene
Graphene-plasmon-polaritons, commonly known simply as “graphene-plasmons”, are a type of polaritons that are formed by the coupling of the electromagnetic field oscillations of light with the charge oscillations of the electrons in the graphene. Graphene-plasmons can be described as waves, which are confined to the atomically thin graphene and propagate along it. They have attracted great interest in the last few years, due to their extraordinary properties of extreme confinement and low loss, especially in the MIR/THz spectra. Their polaritonic nature enables them to shrink the long wavelength of MIR/THz light by several orders of magnitude, and to easily break the diffraction limit.
Excitons in monolayer semiconductors
Monolayers of transition-metal-dichalcogenides (TMDs) are direct bandgap 2D materials semiconductors, which support unique excitons, i.e. the excitation of bound electron-hole pairs. These excitons have very large binding energies, and practically dominate the optical response of the TMDs. They can couple very strongly with light and form different types of exciton-polaritons. The lattice structure of these materials yields a broken inversion symmetry and strong spin-orbit coupling, and thus leads to special selection rules for optical excitations. This lifts the valley degeneracy and enables optical access to the different valleys of the TMD, opening the path to valley-physics phenomena.
Wave properties of polaritons
Polaritons are electromagnetic surface waves that propagate at the interface between a metallic and a dielectric material. These waves exhibit unusual and attractive properties, such as high spatial confinement and enhancement of the optical field, and are widely used in a variety of applications, such as sensing metasurfaces, imaging, and subwavelength optics. Owing to the wave nature of polaritons, it is possible to manipulate and control their properties by various manners. We investigate the existense of new polaritons in 2D materials, and thier wave properties, such as their diffraction from periodical structures, holography, beam shaping, and nonlinear wave mixing.