Floquet Topological Phases and Anomalous Hall Signatures in Irradiated Two-dimensional $d_{xy}$-Wave Altermagnets

Abstract

We study Floquet topological phases in two-dimensional $d_{xy}$-wave altermagnets driven by off-resonant circularly polarized light and subject to an out-of-plane magnetization induced via extrinsic exchange coupling from a proximate ferromagnet. Using a lattice Floquet formulation, we show that the system is governed by a driving parameter $β$ that controls the emergence of distinct gap-closing points and associated topological phases. For $|β|>1$, topology is dominated by anisotropic Dirac points at high symmetry points, leading to Chern phases with $|\mathcal{C}|=2$. For $|β|<1$, light-induced off-symmetry $G$ points appear in four families in the Brillouine zone, enabling higher Chern phases up to $|\mathcal{C}|=4$. Low-energy analysis reveals that high symmetry points host anisotropic massive Dirac fermions, while $G$ points realize generalized two-dimensional anisotropic Dirac points with fully momentum-dependent pseudospin structure, leading to distinct Berry curvature distributions. In the metallic regime, the anomalous Hall conductivity provides an experimental signature of these Floquet topological phases, exhibiting sharp features associated with Berry curvature accumulation near local gap-closing regions.