Tunable Chirality of Floquet Quantum Anomalous Hall Effect in an Altermagnetic Fe2Te2O Monolayer.

Abstract

Altermagnetism is a newly identified magnetic phase, constituting a third class of magnets with momentum-dependent spin splitting but vanishing net magnetic moment. Here, unlike the widely considered circularly polarized light that yields a normal insulating phase, we put forward that Floquet engineering under elliptically polarized light induces Floquet quantum anomalous Hall (QAH) effect in two-dimensional (2D) altermagnets with out-of-plane magnetization. Notably, Floquet-Bloch band engineering enables switchable chirality via manipulating the intensity and/or polar angle. Furthermore, we identify the Fe2Te2O monolayer as a realistic candidate hosting nontrivial phenomena, where topological phase transitions from a topological crystalline insulator (TCI) to a QAH insulator and between QAH insulators with opposite chirality emerge, as confirmed by first-principles calculations. These findings establish the feasibility of realizing the QAH effect in 2D altermagnets and provide an experimentally accessible avenue toward next-generation high-speed, optically controlled topological electronic devices.