标题： 用超快光电子技术追踪石墨烯中的主要热化事件 显示英文标题

标题： Tracking primary thermalization events in graphene with photoemission at extreme timescales

摘要： 直接和逆向俄歇散射是介导半导体中热载流子热化的主要过程。 这些两种过程涉及通过与第三个载流子交换能量而湮灭或生成一个电子-空穴对，该第三个载流子被加速或减速。 逆向俄歇散射通常被抑制，因为被减速的载流子必须具有高于带隙本身的额外能量。 在无带隙的石墨烯中，逆向俄歇散射在最早的时间延迟时被预测占主导地位。 在这里，使用$<8$飞秒极端紫外脉冲来检测这种不平衡，通过时间-角度分辨光电子能谱跟踪激发电子的数量及其动能。 在泵浦脉冲吸收后大约 25 fs 的时间窗口内，我们观察到导带载流子密度增加，同时平均载流子动能减少，这表明弛豫实际上是由逆向俄歇散射主导的。 通过光电子能谱在极端时间尺度上测量载流子散射，将为皮赫兹电子学中固体电子性质的超快控制提供指导。 显示英文摘要

摘要： Direct and inverse Auger scattering are amongst the primary processes that mediate the thermalization of hot carriers in semiconductors. These two processes involve the annihilation or generation of an electron-hole pair by exchanging energy with a third carrier, which is either accelerated or decelerated. Inverse Auger scattering is generally suppressed, as the decelerated carriers must have excess energies higher than the band gap itself. In graphene, which is gapless, inverse Auger scattering is instead predicted to be dominant at the earliest time delays. Here, $<8$ femtosecond extreme-ultraviolet pulses are used to detect this imbalance, tracking both the number of excited electrons and their kinetic energy with time- and angle-resolved photoemission spectroscopy. Over a time window of approximately 25 fs after absorption of the pump pulse, we observe an increase in conduction band carrier density and a simultaneous decrease of the average carrier kinetic energy, revealing that relaxation is in fact dominated by inverse Auger scattering. Measurements of carrier scattering at extreme timescales by photoemission will serve as a guide to ultrafast control of electronic properties in solids for PetaHertz electronics.