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arXiv · 2608.07374

Type-II Mirror Chern Insulator in Altermagnets

Amrita Mukherjee·Pritesh Srivastava·Rahul Verma·Bahadur Singh
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Abstract

Altermagnets with momentum-dependent spin splitting despite zero net magnetization can support unique topological states under broken time-reversal symmetry. We predict a mirror-symmetry-protected topological crystalline insulator with momentum-separated edge modes in a two-dimensional altermagnet. Using a square-octagon lattice model, we show that altermagnetic order generates symmetry-related valley-polarized Dirac nodes, which are gapped by spin-orbit coupling to yield a mirror Chern insulator with $C_{\mathcal{M}}=2$. In contrast to conventional mirror Chern insulators, where the two mirror-protected edge modes cross at the same momentum to form a Dirac cone, altermagnetic spin splitting and valley-selective band inversion separate these edge modes in momentum. We refer to this phase as a type-II mirror Chern insulator. We further propose a PbSe/$\mathrm{V_2Se_2O}$ heterobilayer as a candidate material for realizing this phase through the altermagnetic proximity effect. Our results establish altermagnetism as a route to mirror-protected topological phases with momentum-separated edge modes.

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Amrita Mukherjee, Pritesh Srivastava, Rahul Verma, Bahadur Singh. 2026-08-07. Type-II Mirror Chern Insulator in Altermagnets. https://arxiv.org/abs/2608.07374

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