Enhanced Topological Surface State Mediated Transport Elevates Thermoelectric Performance in SnSb2Te4 Quantum Material

The discovery of topological quantum materials harboring Dirac-like massless surface states with high charge carrier mobility presents an exciting opportunity for unlocking superior thermoelectric (TE) performance, contingent upon accessing the unique properties of nontrivial topological surface states (TSS). However, harnessing these exotic TSS properties necessitates precise positioning of the Fermi level (EF) within the insulating bulk band gap. Unfortunately, inherent bulk defects often result in the EF being submerged deep into the bulk bands, rendering the contribution of TSS to electronic transport negligible. Herein, to address this challenge, we devised a novel strategy to augment TSS-mediated electronic transport in a topological insulator, SnSb2Te4, by fine-tuning the EF within the valence band through iodine (I) doping. Through extensive investigation of low-temperature electronic and magneto-transport, we have successfully demonstrated the systematic access to TSS upon I doping, unveiling fascinating quantum diffusive transport phenomena. Our findings reveal a gradual enhancement in the phase coherence length originating from TSS-mediated weak antilocalization, accompanied by a simultaneous reduction in bulk-state-dominated electron–electron interactions upon I doping, significantly elevating carrier mobility. Moreover, while aliovalent doping of I– at the Te2– site orchestrates an optimized p-type carrier concentration, leading to an amplified Seebeck coefficient, the introduction of I doping-induced point defects disrupts phonon propagation in the inherently low thermally conductive SnSb2Te4. As a result, we achieved a promising TE figure of merit of zT ∼0.55 in I-doped SnSb2Te4.