Electronic, Magnetic, Topological, and Optical Properties

This chapter presents a comprehensive overview of the electronic, magnetic, topological, and optical properties of representative two-dimensional (2D) quantum materials. The discussion begins with Dirac fermion physics and the half-integer quantum Hall effect in graphene, followed by superconductivity and emergent quantum phenomena in twisted bilayer graphene (TBG). The quantum spin Hall effect in graphene-derived systems – such as silicene, germanene, stanene, bismuth bilayers, bismuthene, and 1T′-WTe 2 – is then examined. Distinctive optical responses of transition metal dichalcogenide monolayers, including valley-selective circular dichroism and second-harmonic generation (SHG), are highlighted. Anisotropic electronic properties in phosphorene, 2D ferroelectricity in monolayer group-IV monochalcogenides and α-In 2 Se 3 , and multiferroicity in monolayer NiI 2 are also discussed. The chapter concludes with recent advances in 2D magnetism, encompassing Cr- and Fe-based van der Waals (vdW) magnets, antiferromagnetism in monolayer FePS 3 , and candidate quantum spin liquid behavior in α-RuCl 3 and selected 1T-phase transition metal dichalcogenide monolayers.