The discovery of two dimensional (2D) atomically thin crystals has changed the way we think about materials. Because all the atoms in any 2D crystal are exposed to our three-dimensional world, it has become possible for the first time to tune the electronic properties of a material without changing its chemical composition, for example by introducing strain, plucking out atoms, or intentionally stacking of 2D crystals in various ways. When two such crystals are placed on top of each other, their mutual Van der Waals interactions can radically change their properties, leading to essentially new materials in terms of the electronic band structure. One of the simplest techniques, changing the relative orientation of superposed 2D crystals, has proven to be especially impactful and has taken center stage recently following the surprising discovery of interaction induced insulating states and superconductivity in twisted bilayer graphene. In this talk I will discuss the rapidly evolving field of twisted 2D crystals from its serendipitous discovery to recent developments.
