In graphene each carbon atom has three electrons that are bound to electrons in neighboring atoms, forming chemical bonds. The fourth electron of each atom is “delocalized” throughout the whole graphene sheet, which allows it to conduct electrical current. At the same time, the forbidden zone in the graphene has zero width. If you plot the electron energy and their location in graph form, you get a figure resembling an hour glass, i.e. two cones connected by vertices. These are known as Dirac cones.
Due to this unique condition, electrons in graphene behave very strangely: all of them have one and the same velocity (which is comparable to the velocity of light), and they possess no inertia. They appear to have no mass. And, according to the theory of relativity, particles traveling at the velocity of light must behave in this manner. The velocity of electrons in graphene is about 10 thousand kilometers a second (electron velocities in a typical conductor vary from centimeters up to hundreds of meters per second).
Phagraphene, discovered by Oganov and his colleagues through the use of the USPEX algorithm, as well as graphene, is a material where Dirac cones appear, and electrons behave similar to particles without mass.