Intrinsic High Chern Numbers in Two-Dimensional M_{2}X_{2} Materials

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Monolayer M₂X₂ compounds share a common lattice structure but exhibit distinct quantum anomalous Hall (QAH) phases.
• The underlying mechanisms for these distinct Chern numbers (C) are not fully understood.
• Exploring these mechanisms is crucial for understanding and engineering topological materials.

Purpose of the Study:

• To identify and elucidate the generic band-inversion mechanisms responsible for different Chern numbers in monolayer M₂X₂ compounds.
• To provide a unified explanation for QAH phases in related 2D systems.
• To offer practical guidance for designing and screening materials with tunable high-Chern-number topological properties.

Main Methods:

• First-principles calculations to investigate electronic band structures.
• Symmetry analysis to understand topological properties.
• Tight-binding models to capture low-energy electronic behavior.
• Analysis of orbital composition and symmetry representations of 3d states near the Fermi level.

Main Results:

• Two distinct band-inversion mechanisms identified, governed by orbital composition and symmetry.
• Dominance of dₓz and d<0xE1><0xB5><0xA7>z orbitals leads to a doubly degenerate Γ-point inversion, resulting in C=1.
• Inversions at Γ-X and Γ-Y momenta, driven by other orbital compositions, yield C=2 through additive Berry-curvature contributions.
• The proposed mechanisms consistently explain QAH phases in various 2D systems, including LiFeSe, KTiSb, MgFeP, and Janus M₂X₂ derivatives.

Conclusions:

• The identified band-inversion mechanisms provide a fundamental understanding of distinct Chern numbers in M₂X₂ materials.
• This work offers practical insights for the rational design and discovery of novel topological insulators.
• The findings pave the way for engineering materials with tunable high-Chern-number topological states for potential applications.