Light incident upon materials can induce changes in their electrical conductivity, a phenomenon referred to as photoresistance. In semiconductors, the photoresistance is negative, as light-induced promotion of electrons across the bandgap enhances the number of charge carriers participating in transport. In superconductors and normal metals, the photoresistance is positive because of the destruction of the superconducting state and enhanced momentum-relaxing scattering, respectively. Here we report a qualitative deviation from the standard behaviour in doped metallic graphene. We show that Dirac electrons exposed to continuous-wave terahertz (THz) radiation can be thermally decoupled from the lattice, which activates hydrodynamic electron transport. In this regime, the resistance of graphene constrictions experiences a decrease caused by the THz-driven superballistic flow of correlated electrons. We analyse the dependencies of the negative photoresistance on the carrier density, and the radiation power, and show that our superballistic devices operate as sensitive phonon-cooled bolometers and can thus offer, in principle, a picosecond-scale response time. Beyond their fundamental implications, our findings underscore the practicality of electron hydrodynamics in designing ultra-fast THz sensors and electron thermometers.

入射到材料上的光会引起其导电性的变化，这种现象称为光阻。在半导体中，光阻为负，因为光诱导的电子跨带隙的促进增加了参与传输的电荷载流子的数量。在超导体和普通金属中，光阻为正，因为超导态的破坏和动量松弛散射的增强分别是正的。在这里，我们报告了掺杂金属石墨烯中与标准行为的定性偏差。我们表明，暴露于连续波太赫兹 （THz） 辐射的 Dirac 电子可以与晶格热解耦，从而激活流体动力学电子传递。在这种状态下，石墨烯收缩的电阻由相关电子的太赫兹驱动的超弹道流引起降低。我们分析了负光阻对载流子密度和辐射功率的依赖性，并表明我们的超弹道器件作为灵敏的声子冷却辐射热计运行，因此原则上可以提供皮秒级响应时间。除了其基本意义之外，我们的研究结果还强调了电子流体动力学在设计超快太赫兹传感器和电子温度计方面的实用性。