Two pieces of graphite rub against each other, and the resistance vanishes as if an invisible film of oil separated them. Previously, this was only seen under a microscope, on tiny contact patches.
Graphene is a carbon film exactly one atom thick. Two such sheets placed on top of each other with a slight twist behave very differently from a single sheet. At an angle of about 1.1 degrees, electrons slow down so much that the material can become a superconductor or an insulator — depending on the conditions.