The intensity of an electric current running through a metal is directly proportional to the voltage applied. This linear relationship, called Ohm’s law, is sometimes taken to be a defining characteristic of metals; the constant ratio of voltage to intensity is the electrical resistance of a given substance.
Jeehoon Kim at Pohang University of Science and Technology in South Korea and his collaborators found that, in a particular type of bismuth antimonide crystal, the electrical resistance is not constant but changes with voltage. This effect is due to a topological quirk in the energy levels of electrons that allows some of these particles to flow without resistance, and the fact that the number of such electrons varies with voltage.
Similar deviations from Ohm’s law in other materials could be used as easier experimental signatures of such topological effects, which have tended to require expensive synchrotrons to demonstrate.