Two-Dimensional Altermagnetic Iron Oxyhalides: Real Chern Topology and Valley-Spin-Lattice Coupling

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Altermagnets are a novel class of collinear magnetic materials with unique spin-split band structures.
• Topological insulating states are rare in intrinsic altermagnetic systems.
• Exploring new materials for topological states is crucial for quantum technologies.

Purpose of the Study:

• To identify new 2D altermagnetic materials exhibiting topological insulating states.
• To investigate the properties of monolayer Fe2X2O for potential spintronics and valleytronics applications.
• To explore the interplay of altermagnetism, topology, and multiferroicity.

Main Methods:

• First-principles calculations were used to predict material properties.
• Analysis of electronic band structures and topological invariants (real Chern numbers).
• Investigation of spin-polarized valleys and their coupling to external stimuli (light, strain).

Main Results:

• Monolayer Fe2X2O (X = Cl, Br, I) identified as 2D altermagnetic real Chern insulators.
• Materials exhibit d-wave altermagnetic ordering, semiconducting band gaps, and nontrivial real Chern numbers.
• Discovery of spin-polarized topological corner modes and spin-polarized valleys with strong coupling.
• Demonstration of valley-selective excitation and strain-induced valley polarization.
• In Fe2Cl2O, coexistence of magnetism and ferroelasticity, with strain-tunable Néel vector.

Conclusions:

• Monolayer Fe2X2O represents a new family of 2D altermagnetic real Chern insulators.
• These materials possess unique properties for spintronics and valleytronics, including topological corner modes and valley-selective phenomena.
• The interplay of altermagnetism, topology, and multiferroicity in these 2D materials opens new avenues for fundamental research and device applications.