Topological Magnetoelectric Effect in Magnetic Topological Insulator Heterostructures

In the presence of time-reversal symmetry (TRS), topological insulators (TIs) support gapless, linearly-dispersed fermion excitations on their surfaces, characterized by spin-momentum locking. Yet, TIs are more fundamentally defined as bulk magnetoelectrics. In TI thin films, where TRS is broken by two-dimensional (2D) surface magnetism to produce an axion insulator phase, a quantized topological magnetoelectric effect (TME) emerges, closely related to the quantum anomalous Hall effect. In this work, by employing state-of the-art first-principles methods combined with atomistic tight-binding models and non-equilibrium Green's functions for quantum transport, we have addressed theoretically some outstanding issues related to the robust realization of the TME in novel 2D van der Waals (vdW) magnetic TI heterostructures. Based on the fundamental understating provided by this study, we have explored the use of the TME as a means of controlling the quantum state of vdW multiferroic junctions in heterostructures consisting of TI thin films coupled to 2D magnetic monolayers. The final goal of the project is the design and characterization of radically new nanospintronic devices that rely on interactions and vertical electronic transport across the vdW gaps of the heterostructures.