Super-collimation and negative refraction in hyperbolic Van der Waals superlattices

Abstract

In this paper, we investigate supercollimation and negative group refraction properties of Van der Waals crystals. Van der Waals crystals, such as Bi 2 Se 3 , show both type I and type II hyperbolic dispersion at terahertz (THz) frequencies. An all angle negative group index of refraction is observed at frequencies that exhibit type I hyperbolic dispersion. However, a negative group index of refraction is observed at higher angles in the type II spectral region. The supercollimation effect is achieved at the inversion point of type II and the Reststrahlen band, where the resonance cone angle is close to zero. We further show broadband tunable hyperbolic dispersion from THz to mid infrared frequencies and a widening of the negative group index spectral band using topological insulator–dielectric insulator based superlattice structures.