Shaping terahertz waves using anisotropic shear modes in a van der Waals mineral

Author(s)

Kawahala, Nicolas M. ; Matos, Daniel A. ; de Oliveira, Raphaela ; Longuinhos, Raphael ; Ribeiro-Soares, Jenaina ; Barcelos, Ingrid D. ; Hernandez, Felix G. G.

• Document type: Journal article
• Source: NPJ 2D MATERIALS AND APPLICATIONS; v. 9, n. 1, p. 7-pg., 2025-02-19.

Abstract

The interlayer interactions in van der Waals (vdW) materials are imprinted in their low-frequency rigid-layer phonon spectra. Investigating the symmetries of these phonon modes offers a pathway to generate optical anisotropy in the terahertz range. Here, we employ polarization-sensitive terahertz time-domain spectroscopy to study a sample of clinochlore, a naturally abundant, large bandgap vdW mineral. Our measurements revealed a pronounced anisotropic feature in the complex refractive index spectrum near 1.13 THz, consistent with shear modes predicted by our density-functional perturbation theory that accounts for impurities in the mineral. Polarimetry analysis revealed that this shear phonon anisotropy reshapes the polarization state of transmitted terahertz waves, inducing both Faraday rotation and ellipticity. Furthermore, we applied Jones formalism to interpret the phononic symmetries and describe our observations in terms of its polarization eigenstates. These results highlight the potential of exploring vdW minerals as central building blocks for vdW heterostructures with compelling technological 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: 21/12470-8 - Research in quantum materiais involving intense magnetic fields and low temperatures
• Grantee: Gennady Gusev
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 23/04245-0 - Terahertz phonons in quantum materials
• Grantee: Felix Guillermo Gonzalez Hernandez
• Support Opportunities: Regular Research Grants
• FAPESP's process: 23/11158-6 - Time-domain THz spectroscopy in quantum materials
• Grantee: Nícolas Massarico Kawahala
• Support Opportunities: Scholarships in Brazil - Technical Training Program - Technical Training
• 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