Giant Photonic Response of Mexican-hat Topological Semiconductors for Mid-infrared to THz Applications

TL;DR

This paper shows that Mexican-hat band structure topological insulators exhibit giant optical responses in the mid-infrared to THz range, offering promising applications in photonics and quantum technologies.

Contribution

It identifies and characterizes Mexican-hat band structure topological insulators with large optical responses suitable for MIR/FIR/THz applications.

Findings

Optical responses of MHBS TIs are 10-100 times larger than normal semiconductors.

Discovered MHBS TIs with bandgaps 0.05-0.5 eV and high absorption coefficients.

Potential for enhanced MIR/FIR/THz photonic devices.

Abstract

The mid-infrared (MIR), far-infrared (FIR) to terahertz (THz) frequencies are the least developed parts of the electromagnetic spectrum for applications. Traditional semiconductor technologies like laser diodes and photodetectors are successful in the visible light range, but are still confronted with great challenges when extended into the MIR/FIR/THz range. In this paper, we demonstrate that topological insulators (TIs), especially those with Mexican-hat band structure (MHBS), provide a route to overcome these challenges. The optical responses of MHBS TIs can be one to two orders of magnitude larger than that of normal semiconductors at the optical-transition edge. We explore the databases of topological materials and discover a number of MHBS TIs whose bandgaps lie between $0.05\sim 0.5~\rm eV$ and possess giant gains (absorption coefficients) on the order of $10^4 \sim 10^5~\rm cm^{-1}$ at the transition edge. These findings may significantly boost potential MIR/FIR/THz applications such as photon sources, detectors, ultrafast electro-optical devices, and quantum information technologies.