Quantum phase transition refers to the abrupt change of ground states of many-body systems driven by quantum fluctuations. It hosts various intriguing exotic states around its quantum critical points approaching zero temperature. Here we report the spectroscopic and transport evidences of quantum critical phenomena of an exciton Mott metal-insulator-transition in black phosphorus. Continuously tuning the interplay of electron-hole pairs by photo-excitation and using Fourier-transform photo-current spectroscopy as a probe, we measure a comprehensive phase diagram of electron-hole states in temperature and electron-hole pair density parameter space. We characterize an evolution from optical insulator with sharp excitonic transition to metallic electron-hole plasma phases featured by broad absorption and population inversion. We also observe strange metal behavior that resistivity is linear in temperature near the Mott transition boundaries. Our results exemplify an ideal platform to investigating strongly-correlated physics in semiconductors, such as crossover between superconductivity and superfluity of exciton condensation.

量子相变是指由量子涨落驱动的多体系统基态的突变。它在接近零温度的量子临界点周围拥有各种有趣的奇异状态。在这里，我们报告了黑磷中激子莫特金属-绝缘体-跃迁的量子临界现象的光谱和传输证据。通过光激发连续调整电子-空穴对的相互作用，并使用傅里叶变换光电流谱作为探针，我们测量了温度和电子-空穴对密度参数空间中电子-空穴状态的综合相图。我们描述了从具有急剧激子跃迁的光学绝缘体到具有广泛吸收和粒子数反转特征的金属电子-空穴等离子体相的演变过程。我们还观察到奇怪的金属行为，即电阻率在莫特转变边界附近的温度呈线性。我们的结果举例说明了研究半导体中强相关物理的理想平台，例如超导性和激子凝聚过剩之间的交叉。