Interfacial physics in van der Waals heterostructures

Abstract

Van der Waals layered materials are weakly bonded between layers. They can be exfoliated down to atomically thin flakes with atomically clean surfaces. Unlike conventional two-dimensional (2D) systems, electronic wave functions in these atomically thin materials are directly exposed to the surface. Materials with different properties can be readily stacked together, creating quantum simulators for various new physics. Specifically, symmetry-breaking orders can be introduced in trivial materials through the proximity effect, such as the magnetic proximity effect and superconducting proximity effect. The short-range proximity interaction can strongly modify the material properties and generates exotic quantum states that cannot appear in a single material. A recent revolutionary use of 2D materials is to create a super-lattice potential on the 2D material interfaces. By mis-aligning or mismatching different 2D materials, moire super-lattices are created with lattice constants that are orders of magnitude larger. These moire lattices provide the best solid-state quantum simulators for both strong correlation and topological physics, with temperatures comfortably reachable by current experimental techniques. In this thesis, I will focus on the interface effect of 2D materials heterostructures. Combining electrical transport and tunneling spectroscopy measurements, we study the Berry curvature effect, the proximity effect, and the moire super-lattice effect in various 2D material heterostructures. Firstly, I will introduce the van der Waals 2D materials in general. Secondly, I will show the Berry curvature dipole effects in 1T' WTe2. Thirdly, I will present quasi-particle and Josephson tunneling measurements in superconductor/ferromagnetic insulator heterostructures. Lastly, I will show both theoretical and experimental simulations of topological and correlation physics in twisted homo-bilayer MoTe2 moire lattice and aligned bilayer WTe2/WSe2 moire lattice. This thesis demonstrates the exceptional advantages of 2D materials in building hetero-structures and shows their promising future for solid state simulators for many new physics.