In-plane transport and enhanced thermoelectric performance in thin films of the topological insulators Bi_2Te_3 and Bi_2Se_3

TL;DR

This paper investigates in-plane transport in thin films of topological insulators Bi_2Te_3 and Bi_2Se_3, revealing how surface state hybridization affects thermoelectric performance and conductivity behavior.

Contribution

It provides new insights into how surface state hybridization influences thermoelectric efficiency and localization phenomena in thin topological insulator films.

Findings

Hybridization induces a tunable band gap affecting thermoelectric performance.

Conductivity transitions from anti-localization to localization with changing conditions.

Surface states contribute significantly to in-plane transport properties.

Abstract

Several small-bandgap semiconductors are now known to have protected metallic surface states as a consequence of the topology of the bulk electron wavefunctions. The known "topological insulators" with this behavior include the important thermoelectric materials Bi_2Te_3 and Bi_2Se_3, whose surfaces are observed in photoemission experiments to have an unusual electronic structure with a single Dirac cone. We study in-plane (i.e., horizontal) transport in thin films made of these materials. The surface states from top and bottom surfaces hybridize, and conventional diffusive transport predicts that the tunable hybridization-induced band gap leads to increased thermoelectric performance at low temperatures. Beyond simple diffusive transport, the conductivity shows a crossover from the spin-orbit induced anti-localization at a single surface to ordinary localization.