Hydrogen‐Functionalized Two‐Dimensional H‐Phase Janus TiXYH (X = Cl, Br; Y = P, As): Valley Electronics and Multiple Magnetic States

ABSTRACT

Integrating spin, valley, and topology in a single tunable 2D platform is highly desirable for multifunctional quantum technologies. Here, we identify Janus TiXYH (X = Cl, Br; Y = P, As) as a versatile quantum‐material family in which these degrees of freedom are strongly coupled from the monolayer to the bilayer limit. In the monolayer form, polar TiXYH is an intrinsic ferromagnetic semiconductor with sizable valley polarization and finite Berry curvature, giving rise to an anomalous valley Hall response. More importantly, strain effectively reshapes the band topology and drives a transition toward a quantum anomalous Hall state, enabling topology‐assisted control of valley physics. In bilayers, interlayer sliding introduces switchable ferroelectric polarization and reconfigures the Berry‐curvature distribution, resulting in an electrically reversible layer‐polarized anomalous Hall effect with tunable valley polarization. The Hall response can therefore be switched by reversing the ferroelectric polarization. Moreover, interlayer coupling stabilizes antiferromagnetic ordering, while twisting the bilayer induces a staggered magnetic configuration with altermagnetic characteristics. These results establish Janus TiXYH as a programmable 2D platform for strain‐, electric‐field‐, and stacking‐controlled topological and valley quantum functionalities.