Diverse Landscape of Tunable Magnetic, Topological, and Ferroelectric States in 2D Ti(3)Se(3)Te(2).

2D layered materials provide a powerful platform for exploring the intertwined physics of magnetism, topology, and ferroelectricity. Here, using first-principles calculations, we reveal a rich landscape of tunable quantum phases and ferroelectric states in the 2D van der Waals material TiSeTe, controlled by magnetization orientation, stacking configuration, and interlayer sliding. For the monolayer, TiSeTe is identified as a dynamically stable ferromagnet whose magnetization direction drives a phase transition between a trivial metal and a quantum anomalous Hall insulator with a nonzero Chern number. In bilayers, two distinct stacking configurations lead to markedly different behaviors: (i) the AA-stacking bilayer stabilizes an altermagnetic ordering and hosts a quantum spin Hall insulating phase characterized by a nonzero spin Chern number; and (ii) the AA'-stacking bilayer exhibits a three-state in-plane ferroelectricity, beyond the two-state out-of-plane ferroelectricity reported in many altermagnetic systems. Sliding-induced switching in this configuration reversibly modulates the in-plane polarization, the easy-magnetization axis, and the spin splitting. These results demonstrate that TiSeTe integrates tunable topological phases, altermagnetism, and sliding-induced three-state in-plane ferroelectricity, establishing it as a versatile van der Waals platform for low-energy spintronic technologies, topological quantum science, and next-generation multifunctional applications.