Terahertz Twistoptics-Engineering Canalized Phonon Polaritons

Author(s):Show less -

Obst, Maximilian ; Noerenberg, Tobias ; Alvarez-Perez, Gonzalo ; de Oliveira, Thales V. A. G. ; Taboada-Gutierrez, Javier ; Feres, Flavio H. ; Kaps, Felix G. ; Hatem, Osama ; Luferau, Andrei ; Nikitin, Alexey Y. ; Klopf, J. Michael ; Alonso-Gonzalez, Pablo ; Kehr, Susanne C. ; Eng, Lukas M.

• Document type: Journal article
• Source: ACS NANO; v. 17, n. 19, p. 10-pg., 2023-09-22.

Abstract

The terahertz (THz) frequency range is key to studying collective excitations in many crystals and organic molecules. However, due to the large wavelength of THz radiation, the local probing of these excitations in smaller crystalline structures or few-molecule arrangements requires sophisticated methods to confine THz light down to the nanometer length scale, as well as to manipulate such a confined radiation. For this purpose, in recent years, taking advantage of hyperbolic phonon polaritons (HPhPs) in highly anisotropic van der Waals (vdW) materials has emerged as a promising approach, offering a multitude of manipulation options, such as control over the wavefront shape and propagation direction. Here, we demonstrate the THz application of twist-angle-induced HPhP manipulation, designing the propagation of confined THz radiation between 8.39 and 8.98 THz in the vdW material alpha-molybdenum trioxide (alpha-MoO3), hence extending twistoptics to this intriguing frequency range. Our images, recorded by near-field optical microscopy, show the frequency- and twist-angle-dependent changes between hyperbolic and elliptic polariton propagation, revealing a polaritonic transition at THz frequencies. As a result, we are able to allocate canalization (highly collimated propagation) of confined THz radiation by carefully adjusting these two parameters, i.e. frequency and twist angle. Specifically, we report polariton canalization in alpha-MoO3 at 8.67 THz for a twist angle of 50 degrees. Our results demonstrate the precise control and manipulation of confined collective excitations at THz frequencies, particularly offering possibilities for nanophotonic applications. (AU)

• FAPESP's process: 19/14017-9 - From excitons waves to THz-phonons: 2Ds materials nano-optics via synchrotron infrared nanospectroscopy
• Grantee: Raul de Oliveira Freitas
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 22/02901-4 - Nano-optics of polaritons in two-dimensional crystals and at the metal/dielectric interface in the mid-to-far infrared
• Grantee: Francisco Carlos Barbosa Maia
• Support Opportunities: Research Grants - Initial Project