Possible light-induced superconductivity in K3C60 at high temperature

Abstract

By exciting high-temperature K3C60 with mid-infrared pulses, a large increase in carrier mobility is obtained, accompanied by the opening of a gap in the optical conductivity; these same signatures are observed at equilibrium when cooling K3C60 below the superconducting transition temperature of 20 kelvin, which could be an indication of light-induced high-temperature superconductivity. The use of light to control the properties of condensed-matter materials is a promising area of research, with the long-term prospect that it might lead to the development of quantum devices driven by light. In particular, it was shown recently that nonlinear excitation of certain phonons in bilayer copper oxides induces superconducting-like optical properties at temperatures far above the material's superconducting transition temperature (Tc). This effect was accompanied by the disruption of competing charge-density-wave correlations, explaining some, but not all, of the experimental results. Andrea Cavalleri and colleagues now report that by exciting metallic K3C60 with mid-infrared optical pulses, they can induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. Strikingly, these same signatures are observed at equilibrium when K3C60 cools below its Tc of 20 K. The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity1. Nonlinear excitation2,3 of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc (refs 4, 5, 6). This effect was accompanied by the disruption of competing charge-density-wave correlations7,8, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. These same signatures are observed at equilibrium when cooling metallic K3C60 below Tc (20 kelvin). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this as a possible explanation of our results.