Application of an intense light field to solids produces enormous and ultrafast nonlinear phenomena such as high-harmonic generation^1,2 and attosecond charge dynamics^3,4. These are distinct from conventional photonics. However, the main targets for investigation have been limited to insulators and semiconductors, although theoretical approaches have also been developed for correlated metals and superconductors⁵. Here, in a layered organic superconductor, a nonlinear charge oscillation driven by a nearly single-cycle strong electric field of >10 MV cm⁻¹ is observed as a stimulated emission. The charge oscillation is different from a linear response and ascribed to a polar charge oscillation with a period of ∼6 fs. This nonlinear polar charge oscillation is enhanced by critical fluctuations near a superconducting transition temperature and a critical end-point of first-order Mott transitions. Its observation on an ultrafast timescale of ∼10 fs clarifies that Coulomb repulsion plays an essential role in the superconductivity of organic superconductors.

将强光场应用于固体会产生巨大且超快速的非线性现象，例如高次谐波产生^1,2和阿秒电荷动力学^3,4。这些不同于常规的光子学。然而，尽管相关金属和超导体^5的理论方法也得到了发展，但研究的主要目标仅限于绝缘体和半导体。在此，在层状有机超导体中，观察到由> 10 MV cm ^-1的近单周期强电场驱动的非线性电荷振荡作为受激发射。电荷振荡不同于线性响应，归因于极性电荷振荡，周期约为6英尺 通过在超导转变温度附近的临界波动和一阶Mott转变的临界端点，可以增强这种非线性极性电荷振荡。它在约10 fs的超快时间尺度上的观测结果表明，库仑斥力在有机超导体的超导性中起着至关重要的作用。