Ohm’s law is well-known from physics class. It states that the resistance of a conductor and the voltage applied to it determine how much current will flow through the conductor. The electrons in the material – the negatively charged carriers – move in a disordered fashion and largely independently of each other. Physicists find it far more interesting, however, when the charge carriers influence one another strongly enough for that simple picture not to be correct anymore.
This is the case, for instance, in “Twisted Bilayer Graphene”, which was discovered a few years ago. That material is made from two wafer-thin graphene layers consisting of a single layer of carbon atoms each. If two neighbouring layers are slightly twisted with respect to each other, the electrons can be influenced in such a way that they interact strongly with one another. As a consequence, the material can, for instance, become superconducting and hence conduct current without any losses.
Source: “An insulator made of two conductors”, Zurich ETH News