Bulk-surface coupling in dual topological insulator Bi₁Te₁ and Sb-doped Bi₁Te₁ single crystals via electron-phonon interaction

Abstract Recently, B i 1 T e 1 has been proved to be a dual topological insulator (TI), a new subclass of symmetry-protected topological phases, and predicted to be higher order topological insulator (HOTI). Being a dual TI (DTI), Bi 1 Te 1 is said to host quasi-1D surface states (SSs) due to weak TI phase and topological crystalline insulating SSs at the same time. On the other hand, HOTI supports topologically protected hinge states. So, B i 1 T e 1 is a unique platform to study the electrical signature of topological SS (TSS) of fundamentally different origins. Though there is a report of magneto-transport measurements on large-scale Bi 1 Te 1 thin films, the Bi 1 Te 1 single crystal is not studied experimentally to date. Even the doping effect in a DTI Bi 1 Te 1 is missing in the literature. In this regard, we performed the perpendicular and parallel field magneto-transport measurement on the exfoliated microflake of Bi 1 Te 1 and Sb-doped Bi 1 Te 1 single crystals, grown by the modified Bridgmann method. Our metallic sample shows the weak anti-localization behavior analyzed by the multi-channel Hikami-Larkin-Nagaoka equation. We observed the presence of a pair of decoupled TSS. Further, we extracted the dephasing index ( β ) from temperature (T)-dependence of phase coherence length (L ϕ ), following the power law equation (L ϕ ∝ T − β ). The thickness-dependent value of β indicates the transition in the dephasing mechanism from electron-electron to electron-phonon interaction with the increase in thickness, indicating the enhancement in the strength of bulk-surface coupling. Sb-doped system shows weakened bulk-surface coupling, hinted by the reduced dephasing indices.