Phonons polaritons cavity effect in two dimensional hBN and G-hBN heteroestructures

Author(s)

Flávio Henrique Feres

• Document type: Master's Dissertation
• Press: Rio Claro. 2020-10-28.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Geociências e Ciências Exatas. Rio Claro
• Defense date: 2020-05-13
• Advisor: Francisco Carlos Barbosa Maia

Abstract

Optical phenomena of polar van der Waals crystals, on the nanoscale, occur primarily via polaritons, which are quasi-particles originated from the coupling between photons and fundamental resonances of matter. There are different Tipos of polaritons, named according to the presented light-matter interaction: plasmon-polaritons, exciton-polaritons, magnon-polaritons and phonon-polaritons. In this work, we study phonons-polaritons confined in two-dimensional crystals of hexagonal boron nitride (hBN). This crystal pertains to the class of hyperbolic materials, thus, supporting hyperbolic phonon-polaritons (HP²) of subdiffractional wavelength. Hyperbolic polaritons are evanescent modes meaning they are confined to the crystal volume and do not propagate in the free space. Therefore, only near field techniques are able to detect the HP2 waves as the Synchrotron Infrared Nano Spectroscopy (SINS) utilized in this work. By means of SINS, we investigate first the hBN polaritonic response on gold (Au) flat substrates by proposing the Hertzian dipole antenna (HDA) modelling to characterize the HP2 waves. We have recently published this novel approach in journal Nanoscale. Additionally, we study the influence of different type of substrates on HP² waves propagation: (i) in-plane anisotropic substrate composed by Au stripes spaced by Air gaps (Au-Air) and (ii) out-of-plane anisotropic substrate composed by silicon dioxide thin films deposited via sputtering on Au (Au/SiO2). In the first case, we demonstrate the formation of HP² microcavities due to the momentum mismatch at the Au-Air substrate transitions. In the second case, we show modulation of wavelength and group velocity of HP² modes as function of the SiO2 thickness. This work presents pioneer results for the polaritonic area in mid-infrared of two-dimensional crystals (AU)

• FAPESP's process: 18/05425-3 - Cavity effect of the Phonon-Polaritons in Graphene-Hexagonal boron nitride two-dimensional heterostructure
• Grantee: Flávio Henrique Feres
• Support Opportunities: Scholarships in Brazil - Master