Twisted Polaritonic Crystals in Thin van der Waals Slabs

• Published in: Laser & photonics reviews 2022-09, Vol.16 (9), p.n/a
• Main Authors: Capote‐Robayna, Nathaniel, Matveeva, Olga G., Volkov, Valentyn S., Alonso‐González, Pablo, Nikitin, Alexey Y.
• Format: Article
• Language: English
• Subjects: Bragg resonance; Crystal lattices; Crystals; Excitation; hyperbolic polaritons; polaritonic crystal; Polaritons; twisted lattices
• ISSN: 1863-8880; 1863-8899
• DOI: 10.1002/lpor.202200428

Polaritons – hybrid light–mater excitations – are very appealing for the confinement of light at the nanoscale. Recently, a particular interest has been focused on thin anisotropic slabs of van der Waals (vdW) materials supporting polaritons with hyperbolic dispersion, which can exhibit ultrahigh momenta and strongly directional in‐plane propagation and thus promise novel nano‐optical applications in a planar geometry. However, the excitation and manipulation of in‐plane hyperbolic polaritons have not yet been well studied and understood. Here, twisted polaritonic crystals (PCs) are introduced – lattices with periods comparable to the polaritons wavelength rotated with respect to the natural vdW crystal axes – to efficiently excite and control in‐plane hyperbolic polaritons. A general analytical theory valid for an arbitrary PC made in a thin biaxial slab is developed and the excitation of Bragg resonances tunable by the twisting angle is demonstrated. The findings open novel avenues for both fundamental studies of PCs in vdW crystals and the development of midinfrared sensing and photodetection applications. A new concept of a deeply subwavelength polaritonic crystal made in thin biaxial van der Waals crystal slabs is introduced. The axes of the polaritonic crystal are twisted with respect to the natural in‐plane crystal axes of the slab. Such twisting provides a new degree of freedom for the tunability and control of narrow polaritonic resonances emerging at infrared frequencies.