ABSTRACT
Beautiful moiré patterns can be created by stacking and twisting two-dimensional crystals, such as graphene or transition metal dichalcogenides. One of the most fascinating discoveries in recent years is that electrons are strongly affected by these moiré patterns and often exhibit completely unexpected behaviour. For example, twisted bilayer graphene – composed of two (semi-)metallic graphene layers – was observed to exhibit correlated insulator states as well as superconductivity at a magic twist angle of 1.1 degrees. In my talk, I will describe my group’s efforts to understand the electronic, vibrational and optical properties of moiré materials from an atomistic perspective which is challenging because of the large unit cells in these systems (often containing thousands of atoms). To overcome this difficulty, we use linear-scaling ab initio methods as well as ab initio-derived tight-binding models and effective moiré-scale models. These techniques give detailed insights into the material-specific properties of moiré materials, such as the ordering of K-derived and Gamma-derived valence bands.
BIO
Johannes is currently a Reader in Theory and Simulation in the Department of Materials at Imperial College London. He is the Director of the MSc in Advanced Materials Science and Engineering. He obtained a Ph.D. in theoretical physics from Cornell University in 2010 working in the group of Prof. Tomas Arias. From 2010 to 2014, he was a postdoctoral researcher at UC Berkeley and Lawrence Berkeley National Lab in the groups of Prof. Steven Louie and Prof. Marvin Cohen.