Calculation of divergent photon absorption in ultrathin films of a topological insulator

TL;DR

This paper investigates the unique linear and nonlinear photon absorption properties of ultrathin topological insulator films, revealing divergent and enhanced absorption features that can be tuned for advanced nanophotonic applications.

Contribution

It provides the first detailed calculations of divergent and enhanced photon absorption in ultrathin topological insulator films, highlighting their potential for tunable nanophotonic devices.

Findings

Divergent edge singularity in one-photon absorption

Significant enhancement in two-photon absorption

Tunable resonance frequencies via surface state coupling

Abstract

We perform linear and non-linear photon absorption calculations in topological insulator ultra-thin films on a substrate. Due to the unique band structure of the coupled topological surface states, novel features are observed for suitable photon frequencies, including a divergent edge singularity in one-photon absorption process and a significantly enhancement in two-photon absorption process. The resonanct frequencies can be controlled by tuning the energy difference and coupling of the top and bottom surface states. Such unique linear and nonlinear optical properties make ultra-thin films of topological insulators promising material building blocks for tunable high-efficiency nanophotonic devices.