Nonlinear Optics in Magic-Angle Twisted Bilayer Graphene

Magic-angle twisted bilayer graphene (MATBG) has emerged as a prototypical platform for exploring the interplay between topology and strong electronic correlations. It hosts a remarkably rich set of ground states, including anomalous Hall phases, superconductivity, correlated insulating states, charge density waves, and inter-valley coherent order. Despite intense experimental and theoretical efforts, the microscopic origins of many of these phases remain unresolved, and the role of topology and quantum geometry is only beginning to be clarified. In this talk, I will demonstrate how nonlinear optical responses provide powerful and selective probes of these emergent states in MATBG. I will focus on two non-linear processes which generate DC transport signatures: the inverse Faraday effect and the circular photogalvanic effect, which respectively probe the system’s magnetic susceptibility and topological properties. I will show how these effects can be used to study and control emergent correlated states. These results establish nonlinear optics as a versatile tool for probing and controlling correlated and topological phases in quantum materials.