Bulk-surface coupling in dual topological insulator Bi₁Te₁and Sb-doped Bi₁Te ₁ single crystals via electron-phonon interaction

Abstract Recently, Bi1Te1 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, Bi1Te1is said to host quasi-1D surface states (SS) due to weak TI phase and topological crystalline insulating (TCI) surface states at the same time. On the other hand, HOTI supports topologically protected hinge states. So, Bi1Te1 is a unique platform to study the electrical signature of topological SS of fundamentally different origins. Though there is report of magneto-transport measurements on large scale Bi1Te1thin film, the Bi1Te1 single crystal is not studied experimentally till date. Even doping effect in a dual TI Bi1Te1 is missing in literature. In this regard, we performed the perpendicular and parallel field magneto-transport measurement on the exfoliated microflake of Bi1Te1 and Sb-doped Bi1Te1 single crystals, grown by modified Bridgmann method. Our metallic sample shows the weak anti-localization behavior analyzed by multi-channel Hikami-Larkin-Nagaoka equation. We observed the presence of a pair of decoupled topological surface states. Further, we extracted the dephasing index (β) from temperature (T)-dependence of phase coherence length (Lφ), following the power law equation (Lφ / ∝T−β). The thickness dependent value of p indicates the transition in dephasing mechanism from electron-electron to electron-phonon interaction with increase in thickness, indicating the enhancement in the strength of bulk-surface coupling.