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

Abstract

Altermagnets, a novel class of collinear magnetic materials, exhibit unique spin-split band structures, yet topological insulating states in intrinsic altermagnetic systems are rare. Here, we identify monolayer Fe${}_2{X}_2$O ($X$ = Cl, Br, I) as a new family of 2D altermagnetic real Chern insulators. These materials display robust $d$-wave altermagnetic ordering, semiconducting band gaps, and nontrivial real Chern numbers per spin channel, yielding spin-polarized topological corner modes. They also feature spin-polarized valleys with strong altermagnetism-valley-spin-lattice coupling, enabling valley-selective excitation via linear dichroism and strain-induced valley polarization. In multiferroic Fe${}_2$Cl${}_2$O, magnetism coexists with ferroelasticity, and an applied strain can switch the Néel vector. These findings position 2D iron oxyhalides as a promising platform for exploring altermagnetism and magnetic topological states for spintronics and valleytronics.

24 pages, 5 figures