Topological cutoff frequency in a slab waveguide: penetration length in topological insulator walls

Abstract

Electromagnetic waves propagating in a slab waveguide, whose walls consist of three-dimensional topological insulator, experience a topological cutoff frequency, ω θ . Once ω θ depends upon the penetration length of the metallic surface states into the bulk, l, our findings suggest TI-made waveguides as useful apparatus to estimate the microscopic quantity l by measuring the optical response carried out by the macroscopic signature of ω θ .