Ultrafast pulses briefly turn carbon 'buckyballs' into high-temperature superconductor

The most-well-known carbon fullerene, C60, otherwise known as a buckyball, when made into a potassium-containing compound with the chemical formula K3C60, can normally behave as a superconductor below a critical temperature of 20 K. It has now been discovered by an international group of researchers that K₃C₆₀ transforms into a high-temperature superconductor when struck by an ultrafast laser pulse. The material takes on superconductive properties, albeit extremely briefly, up to a temperature of -73°C—almost 100 degrees above the critical equilibrium temperature. The research explains the reason for this mysterious behavior.

K₃C₆₀ is a compound in which purely molecular features coexist alongside metallic properties, a characteristic shared by so-called strongly correlated materials. According to the theory developed by the researchers in this study, the laser beam creates a high-energy molecular excitation—yet to do so, it must absorb heat from the low-energy metallic component, which thus cools. As it is specifically the metallic component involved in conduction, its cooling may lead to a superconductivity phase despite the fact that the external temperature is higher than the critical temperature. The researchers note that this is an example of laser cooling, but with a previously unknown operating mechanism—the phenomenon may enable the manufacture of electronic devices whose properties can be switched by light. Reference: A. Nava et al., Nat. Phys. (2017); doi:10.1038/nphys4288.