PhD Thesis defense: Polaritonic phenomena in twisted van der Waals heterostructures

PhD Program

Speaker

Nathaniel Andrés Capote Robayna
DIPC

When

2024/10/30
12:00

Place

CFM Auditorium

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Nano-optics, Nano-photonics and Nano-plasmonics

Supervisors: Alexey Nikitin (DIPC, Ikerbasque) and Pablo Alonso González (University of Oviedo)

This thesis aims to study the propagation of phonon polaritons - light coupled with matter vibrations - in twisted heterostructures based on van der Waals (vdW) materials. In particular, we focus on α-MoO₃, a material where polaritons exhibit hyperbolic in-plane propagation. Throughout this thesis, we propose different twisted heterostructures designed to manipulate light at the nanoscale. The first heterostructure consists of two twisted α-MoO₃ layers, where, at a specific twist angle, we observe the canalization of light along a single in-plane direction. By adding a third twisted α-MoO₃ layer, we can further manipulate the direction of this in-plane canalized light by varying the rotation angle of the uppermost layer. We also introduce a heterostructure composed of a graphene monolayer on top of an α-MoO₃ layer, demonstrating active control of the polaritons through voltage modulation. Another type of heterostructure investigated includes twisted polaritonic crystals - lattices with periodicities comparable to the polaritonic wavelength - on α-MoO₃ layers, where we show the dependence of Bragg resonances on the orientation of the lattice with respect to the crystallographic axes. Finally, we propose a polaritonic crystal formed by an α-MoO₃ layer on top of a metallic hole array, thus enabling active manipulation of polariton propagation via the rotation angle. Altogether, these findings provide new avenues for manipulating light at the nanoscale via system rotations, contributing to the growing field of twist-optics.