Robust second-order topological insulator in 2D van der Waals magnet CrI₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Physics

Background:

• Two-dimensional (2D) chromium triiodide (CrI₃) is a key material for spintronics and topological physics research.
• Previous studies suggested that 2D CrI₃ monolayers and bilayers were topologically trivial.

Purpose of the Study:

• To investigate the hidden band topology of 2D CrI₃.
• To determine if 2D CrI₃ exhibits non-trivial topological properties.
• To explore the potential of 2D CrI₃ for spintronics applications.

Main Methods:

• Band structure calculations
• Topological invariant analysis (second Stiefel-Whitney number)
• Identification of unique topological states (edge and corner states)

Main Results:

• 2D CrI₃ monolayer and bilayers are identified as second-order topological insulators (SOTIs) with a non-zero second Stiefel-Whitney number (w₂ = 1).
• The non-trivial topology is confirmed by the presence of floating edge states and in-gap corner states.
• These SOTI properties are robust against both ferromagnetic and antiferromagnetic transitions.

Conclusions:

• 2D CrI₃ possesses a non-trivial band topology, functioning as a robust magnetic SOTI.
• The findings offer a deeper understanding of 2D CrI₃'s electronic properties.
• This work presents 2D CrI₃ as a promising material for future spintronics applications.