Observation of ultrafast critical currents in optically-driven high-temperature K₃C₆₀

Most photo-induced functional phases observed quantum materials, which include non-equilibrium ferroelectricity [1], magnetism [2, 3], and superconductivity [4,5,6,7,8,9,10,11], have so far been characterized by measuring their transient optical properties. However, to probe new signatures of the underlying microscopic physics and to open the way to future device applications, it is desirable to integrate and to probe these materials in ultrafast electrical devices. Driven superconductivity is a case in point, as nonlinear transport (critical current) or magnetic field expulsion (Meissner effect) have not been reported to date. Here, we report ultrafast measurements of linear and nonlinear electrical transport in photo-excited thin films of K₃C₆₀, grown by Molecular Beam Epitaxy and patterned with a series of photo-conductive switches connected by high-frequency waveguides. Ultrafast linear and nonlinear transport measurements reveal the emergence of the same critical current response observed immediately below T_c = 20 K. The experiments reported here provide a unique signature of optically induced non-equilibrium superconductivity.

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