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

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Topological insulators (TIs) are crucial for advanced spintronic applications requiring efficient spin manipulation.
• Designing TIs with specific spin properties is essential for developing ultralow-power consumption devices.
• Superlattices offer a platform for engineering novel material properties.

Purpose of the Study:

• To achieve distinct topological states with tailored spin properties in reduced-dimensional TI-superlattices.
• To investigate the effect of controlling termination on the topological and spin properties of TI-superlattices.
• To explore the potential of these engineered materials for high-performance spintronic devices.

Main Methods:

• Fabrication of TI-superlattices, (Bi₂ /Bi₂ Se₃ )-(Bi₂ /Bi₂ Se₃ )_N or (□/Bi₂ Se₃ )-(Bi₂ /Bi₂ Se₃ )_N, using molecular beam epitaxy.
• Control of superlattice termination (Bi₂ or Bi₂ Se₃) to achieve distinct topological states.
• Characterization of spin properties, including spin momentum splitting, inverse Edelstein effect, and spin lifetime.

Main Results:

• Bi₂-terminated superlattices exhibit a single Dirac cone with significant spin momentum splitting (≈0.5 Å^-1) and a pronounced inverse Edelstein effect (coherence length up to 1.26 nm).
• Bi₂ Se₃-terminated superlattices function as dual topological insulators, protected by time reversal and mirror symmetries, with exceptionally long spin lifetimes (up to 1 ns).
• Demonstrated the critical role of dimensionality and dual topological phases in selecting specific spin properties.

Conclusions:

• Controlling termination in TI-superlattices enables the engineering of distinct topological states and spin properties.
• These engineered superlattices show great promise for developing high-performance topological spintronic devices.
• The findings provide a new route for designing advanced materials for ultralow-power spintronics.