Dual Topology as a Fingerprint of Relativistic Altermagnetism in AgF$_2$ Monolayer

TL;DR

This paper reveals that monolayer AgF$_2$ exhibits a dual topological state with non-trivial electron and magnon topology, driven by a ferroelastic distortion, leading to observable thermal Hall effects and hybrid quantum phenomena.

Contribution

It demonstrates the existence of a dual topological state in AgF$_2$, unifying electron and magnon topology driven by a ferroelastic transition, a novel finding in quantum materials.

Findings

Valence bands with Chern numbers $C^E=\pm3$

Magnon spectrum with topological gap and $C^M=\pm1$

Experimental fingerprint in transverse thermal Hall effect

Abstract

Altermagnets have emerged as a fertile ground for quantum phenomena, but topological phases unifying different quasiparticles remain largely unexplored. Here, we demonstrate that monolayer AgF$_2$ hosts a dual topological state, driven by a single ferroelastic distortion. This polar transition breaks inversion symmetry and unleashes relativistic spin-orbit effects, simultaneously imparting non-trivial topology to electrons and magnons. The result is valence bands with opposite Chern numbers, $C^E=\pm3$, and a magnon spectrum with a full topological gap and chiral bands, $C^M=\pm1$. This work realizes topological altermagnonics in a tangible material platform, with a clear experimental fingerprint in the transverse thermal Hall effect. The coexistence of fermionic and bosonic topology in AgF$_2$ opens new directions for designing intrinsically hybrid quantum matter.