Visualizing Tailored Spin Phenomena in a Reduced-Dimensional Topological Superlattice.

Emergent topological insulators (TIs) and their design are in high demand for manipulating and transmitting spin information toward ultralow-power-consumption spintronic applications. Here, distinct topological states with tailored spin properties can be achieved in a single reduced-dimensional TI-superlattice, (Bi2 /Bi2 Se3 )-(Bi2 /Bi2 Se3 )N or (□/Bi2 Se3 )-(Bi2 /Bi2 Se3 )N (N is the repeating unit, □ represents an empty layer) by controlling the termination via molecular beam epitaxy. The Bi2 -terminated superlattice exhibits a single Dirac cone with a spin momentum splitting ≈0.5 Å-1 , producing a pronounced inverse Edelstein effect with a coherence length up to 1.26 nm. In contrast, the Bi2 Se3 -terminated superlattice is identified as a dual TI protected by coexisting time reversal and mirror symmetries, showing an unexpectedly long spin lifetime up to 1 ns. The work elucidates the key role of dimensionality and dual topological phases in selecting desired spin properties, suggesting a promise route for engineering topological superlattices for high-performance TI-spintronic devices.