Topological insulator: It acts as an insulator in its interior but whose surface contains metallic states. It means that it conducts electricity only on their surfaces.Research in this relatively new field has so far focused mainly on the fundamental properties of these materials. Graphene: It is the name given to a flat monolayer of carbon atoms tightly packed into a 2D honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities.