Thermoelectric Effects and Topological Insulators

TL;DR

This review explores how topological insulators exhibit unique thermoelectric properties due to their boundary states, size effects, and topological nature, highlighting potential for enhanced thermoelectric performance and future research directions.

Contribution

It summarizes recent findings on thermoelectric effects in topological insulators, emphasizing size-dependent properties and experimental observations of unconventional phenomena.

Findings

Size effects significantly influence $zT$ in TIs.

Unconventional thermoelectric phenomena observed in 3D TIs.

Surface states can be detrimental if high mobility is not utilized.

Abstract

The recent discovery of topological insulator (TI) offers new opportunities for the development of thermoelectrics, because many TIs (like Bi$_2$Te$_3$) are excellent thermoelectric (TE) materials. In this review, we will first describe the general TE properties of TIs and show that the coexistence of the bulk and boundary states in TIs introduces unusual TE properties, including strong size effects and anomalous Seebeck effect. Importantly, the TE figure of merit $zT$ of TIs is no longer an intrinsic property, but depends strongly on the geometric size. The geometric parameters of two-dimensional TIs can be tuned to enhance $zT$ to be significantly greater than 1. Then a few proof-of-principle experiments on three-dimensional TIs will be discussed, which observed unconventional TE phenomena that are closely related to the topological nature of the materials. However, current experiments indicate that the metallic surface states, if their advantage of high mobility is not fully utilized, would be detrimental to TE performance. Finally we provide an outlook for future work on topological materials, which offers great possibilities to discover exotic TE effects and may lead to significant breakthroughs in improving $zT$.