In-Plane Anisotropy in the Layered Topological Insulator Ta₂Ni₃Te₅ Investigated via TEM and Polarized Raman...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Layered Ta2M3Te5 (M = Pd, Ni) materials are platforms for studying 2D topological insulators (2DTIs).
• These 2DTIs possess exotic properties like spin-momentum locking and Dirac fermions, crucial for advanced electronics.
• Ta2Ni3Te5 exhibits superconductivity under pressure and predicted second-order topology, yet its detailed properties remain underexplored.

Purpose of the Study:

• To investigate the anisotropic crystalline and phononic properties of exfoliated few-layer Ta2Ni3Te5.
• To establish a reliable method for determining sample orientation using Raman spectroscopy.
• To advance the fundamental understanding of Ta2Ni3Te5 as a 2D topological insulator.

Main Methods:

• Transmission electron microscopy (TEM) and electron diffraction for structural analysis.
• Polarized Raman spectroscopy (PRS) to probe vibrational modes and anisotropy.
• Angle-resolved PRS to assign vibrational symmetries and analyze orientation-dependent responses.

Main Results:

• TEM revealed structural anisotropy with preferential [010] crystal orientation.
• Raman spectroscopy identified 15 vibrational modes, including 3 ultralow-frequency modes.
• Angle-resolved PRS assigned 11 modes to Ag and 2 to B3g symmetries, demonstrating orientation-dependent responses.
• Linear dichroism and excitation energy dependence were observed in Raman scattering.

Conclusions:

• The study confirms the anisotropic nature of Ta2Ni3Te5.
• Raman spectroscopy offers a rapid, non-destructive fingerprint for determining sample orientation.
• These findings significantly enhance the fundamental understanding of Ta2Ni3Te5 for 2D topological insulator applications.