Topological Insulators for Thermoelectrics: A Perspective from Beneath the Surface

Thermoelectric properties of topological insulators have traditionally been examined in the context of their metallic surface states. However, recent studies have begun to unveil intriguing thermoelectric effects emerging from bulk electronic states, which have largely been overlooked in the past. Charge transport phenomena through the bulk are especially important under typical operating conditions of thermoelectric devices, necessitating a comprehensive review of both surface and bulk transport in topological insulators. Here, we review thermoelectric properties that are uniquely observed in topological insulators, placing special emphasis on unconventional phenomena emerging from bulk states. We demonstrate that unusual thermoelectric effects arising from bulk states, such as band inversion-driven warping, can be discerned in experiments using a rather simple analysis of the weighted mobility. We believe that there is still plenty to uncover within the bulk, yet our current understanding can already inspire new strategies for designing and discovering topological insulators for next-generation thermoelectrics.