Topological surface Dirac states (TSDSs) generated in three-dimensional topological insulators (3D-TIs) are currently of significant interest for new science and advanced technologies. In contrast to many other thermoelectric materials, 3D-TIs exhibit a significant potential to achieve a large enhancement in thermoelectric power factor (PF=σS2) due to their special topological symmetry. However, only limited experiments and discussions have been made so far for elucidating the thermoelectric properties of TSDS. Herein, we report a large S and PF observed for high-quality single-crystal flakes of Sn-Bi1.1Sb0.9TeS2 (Sn-BSTS). Accurate interpretations that the energy-dependent relaxation times τ(E) play an important role in thermoelectrical transport of 3D-TIs are provided. Among 3D-TIs, Sn-BSTS has the highest bulk insulation and shows intrinsic TSDS transport without bulk contributions, along with its hallmark of quantum integer Hall effect at high temperatures. Based on the longitudinal/transverse electrical transport and the thermoelectric coefficient, τ(E)∝E0.21 is accurately deduced. As a consequence of the energy-dependent τ(E), a large enhancement in both S and PF is obtained (S=58μVK-1 and PF=5.0mWm-1K-2 at 77 K), leading to a large increase of 160% for S and 280% for PF when compared to those of graphene at 77 K. The potential thermoelectric performance of the pure TSDS is discussed based on the Boltzmann transport equations.
ASJC Scopus subject areas
- Materials Science(all)
- Physics and Astronomy (miscellaneous)