Unconventional Topological phase transition in Bi2Te3 family under vacuum anneal

Topological insulators are celebrated for their protected topological surface states, typically manifesting as Dirac cones within the fundamental band gap at time-reversal invariant momentum points in the three-dimensional (3D) Brillouin zone. While the existence of a single strong topological gap, characterized by a non-trivial Z invariant, is well-established for many TIs like Bi2Te and Bi2Se3, identifying systems with multiple strong topological gaps near the Fermi level remains rare. Here, we report the successful fabrication and comprehensive characterization of BiTe, demonstrating it to be a remarkable material possessing three distinct strong topological gaps, each hosting a surface-state Dirac cone. Previous efforts to synthesize such superlattice compounds (Bi)(Bi2Te3) have faced challenges with precise stoichiometric control during growth. Utilizing in-situ annealing of molecular beam epitaxy-grown Bi2Te3 films on Al2O3 substrates. This method uniformly converts Bi2Te3 into high-quality Bi4Te3 across the entire film, offering a significant improvement over prior complex fabrication strategies. Through structural, electronic, and topological investigations, including angle-resolved photoemission spectroscopy, we confirm the phase purity and emergent topological properties of the synthesized Bi4Te3. Our findings establish Bi4Te3 as a compelling platform for exploring novel topological phenomena arising from the interplay of multiple topological gaps and their associated surface states. This work not only provides a robust fabrication pathway for complex topological superlattices but also expands the understanding of topological phases in the Bi-Te material system.