Nano-optics of polaritons in two-dimensional crystals and at the metal/dielectric interface in the mid-to-far infrared

Abstract

Polaritons are quasi-particles originated from the coupling between photons and elementary resonances of matter. In the recent years, research on the wave and corpuscular behavior of different types of polaritons in two-dimensional (2D) crystals has greatly contributed to the understanding of novel aspects of nano-optics. Types of polaritons that have been the protagonist in such studies are the hyperbolic phonon-polaritons (hyperbolic phonon-polariton, HPhP) of 2D crystals of hexagonal-phase boron nitride (hexagonal boron nitride, hBN) and ±-molybdenum trioxide (±-MoO3) and plasmon-polaritons of graphene surfaces (surface plasmon-polaritons, SPP) and the metal/dielectric interface. Amidst the remarkable optical properties and effects featured by those polaritons, one can be highlighted the electronically adjustable wavelength of graphene SSPs, the acceleration of HPhP pulses in 2D crystals supported by metal-dielectric heterostructures, the Cherenkov effect of HPhP modes and configurable waveguiding and topological transition of HPhPs in ±-MoO3 twisted heterostructures. Prospects of applications envisage that, in analogy to the electron for electronics, polaritons can become the information carriers of future ultra-compact optical devices entirely constructed by 2D materials and with operation based on their logical properties. These reasons motivate this research project that aims to study scientific cases associated with 2D systems, not yet explored in the literature, which involve the propagation of polaritons in the high technological interest regions of the mid- and far-infrared (TeraHertz spectral region, THz). In the case 1 propagation of polariton waves in polaritonic media lying on anisotropic substrates and in spectral regions of epsilon near-zero (ENZ) created by phonon resonances will be addressed. Both anisotropic substrates and ENZ resonances can change the polariton wavelength and propagation length in well-defined directions, thus, offering means to induce directionality to these waves. In the case 2 tunable Fabry-Perot polaritonic modes in nanocavities of hyperbolic crystals will be investigated aiming at controlling light in nanocavities of boundary conditions modifiable by electronic stimuli. Such tunable nanocavities present promising nanoantenna functionalities that are highly desirable features of components of future information exchange 2D devices. These cases will be thesis subjects of two doctorates. Samples and devices will be built at the Microscopic Samples Laboratory at Sirius and at the Devices Laboratory of the National Nanotechnology Laboratory (LNNano) and will be supported by researcher Ingrid D. Barcelos (LNLS and researcher associated with this project). The polaritonic responses will be characterized via scattering-scanning near field optical microscopy (s-SNOM) and synchrotron infrared nano spectroscopy (SINS). Both are modern optical imaging techniques that use nanometer probes with high spatial resolution (lateral resolution ~25 nm) and momentum compatible with polaritons in 2D systems. Thereby, SINS and s-SNOM can allow complete mapping of the polaritonic waves in the mentioned cases. SINS and s-SNOM in the mid-infrared will be performed on the Imbuia line of Sirius. The case 1 will be also probed by s-SNOM in THz at the Free Electron Laser in Dresden, Germany, in collaboration with researchers Dr. Lucas Eng and Dr. Susanne Kehr from Dresden University of Technology. The investigation of new nanophotonic phenomena of 2D materials and devices proposed here has real potential to generate significant scientific impact, broaden horizons for future research and serve as a basis for the development of technologies based on polaritons in 2D platforms. (AU)