Chiral Magnetism in Intercalated Transition Metal Dichalcogenides Studied by Nonlinear Optics

Transition metal dichalcogenides (TMDCs) intercalated with magnetic atoms have been predicted to host exotic two-dimensional spin textures owing to their strong spin-orbit coupling. One of the anticipated spin textures is chiral helimagnetism in which a periodic rotation of magnetic moments emerges within the plane perpendicular to its propagation direction. While point groups lacking both mirror and inversion symmetries are prerequisites for realizing robust helical structure, systematic experimental studies of the full structural and magnetic symmetries remain missing. Optical second harmonic generation (SHG) probe, which is sensitive to crystallographic and magnetic point group symmetries and capable of coupling to complex spin textures, provides unique opportunities to explore the physics of two-dimensional chiral magnets and serve as guidance to discover new magnetic materials with chirality. Here, we report our studies on helimagnet TMDC candidates, V- and Cr-intercalated NbS₂ and TaS₂, using static and dynamic optical SHG. We will show how we track the complete symmetry evolutions across their magnetic critical temperatures by performing temperature-dependent rotation anisotropy SHG spectroscopy measurements and image the structural and magnetic domains by conducting scanning SHG microscopy measurements.