Giant resonant enhancement for photo-induced superconductivity in K${}_3$C${}_{60}$

Abstract

Photo-excitation at terahertz and mid-infrared frequencies has emerged as a new way to manipulate functionalities in quantum materials, in some cases creating non-equilibrium phases that have no equilibrium analogue. In K${}_3$C${}_{60}$, a metastable zero-resistance phase was documented with optical properties and pressure dependences compatible with non-equilibrium high temperature superconductivity. Here, we report the discovery of a dominant energy scale for this phenomenon, along with the demonstration of a giant increase in photo-susceptibility near 10 THz excitation frequency. At these drive frequencies a metastable superconducting-like phase is observed up to room temperature for fluences as low as ~400 $\hat{I}¼J/c{m}^2$. These findings shed light on the microscopic mechanism underlying photo-induced superconductivity. They also trace a path towards steady state operation, currently limited by the availability of a suitable high-repetition rate optical source at these frequencies.

35 pages, 13 figures, including supplementary