Measurements on micrometer-scale cadmium samples provide definitive evidence of an unusual charge-transport regime in a 3D metal.

In an ordinary metal, electrons undergo collisions with impurities, phonons (lattice vibrations), and material boundaries. By removing momentum from the electrons, these collisions determine the metal’s conductivity. One of these types of collisions—between electrons and phonons—becomes more frequent at high temperatures, further impeding the electron flow and decreasing the metal’s conductivity as it warms. But more than 60 years ago, the physicist Radii Gurzhi predicted that, under certain circumstances, some metals might behave more like classical liquids, in which thermal energy reduces the fluid’s internal resistance to flow, or viscosity, causing conductivity to increase with temperature [1]. Despite having been studied theoretically for decades, the so-called Gurzhi effect was only recently confirmed in graphene [2], following tentative observations in potassium [3].