# A tunable flat terahertz lens using Dirac semimetals: a simulation study

## TL;DR

Researchers designed a tunable terahertz lens using Dirac semimetals and photonic crystals through simulations.

## Contribution

A novel tunable flat terahertz lens design using Dirac semimetals and graded index photonic crystals is proposed.

## Key findings

- The lens design uses Dirac semimetals to achieve tunability via Fermi energy level changes.
- Simulations show the structure works for both transverse magnetic and transverse electric polarizations.
- The graded index photonic crystal enables light focusing with slight rod radius variations.

## Abstract

We propose and design a flat and tunable terahertz lens achieved through a two-dimensional photonic crystal composed of an array of rods made of a Dirac semimetal placed in air as the background medium. The structure of interest is a graded index photonic crystal, made possible by the slight variations in the rods’ radii in a direction perpendicular to the direction of the light propagation. Dirac semimetals' ability to respond to variations in their Fermi energy level manifested as a change in the refractive index provides the tunability of our proposed lens. The interaction of electromagnetic waves with the designed structure is investigated for both transverse magnetic and transverse electric polarizations using two-dimensional finite-difference time-domain method.