Exploring low-loss two-dimensional plasmon modes is considered central for achieving light manipulation at the nanoscale and applications in plasmonic science and technology. In this context, pump–probe spectroscopy is a powerful tool for investigating these collective modes and the corresponding energy transfer processes. Here, I present a first-principles study on non-equilibrium Dirac plasmon in graphene, wherein damping channels under ultrafast conditions are still not fully explored. The laser-induced blueshift of plasmon energy is explained in terms of thermal increase of the electron–hole pair concentration in the intraband channel. Interestingly, while damping pathways of the equilibrium graphene plasmon are entirely ruled by scatterings with acoustic phonons, the photoinduced plasmon predominantly transfers its energy to the strongly coupled hot optical phonons, which explains the experimentally-observed tenfold increase of the plasmon linewidth. The present study paves the way for an in-depth theoretical comprehension of plasmon temporal dynamics in novel two-dimensional systems and heterostructures.

探索低损耗二维等离子体模式被认为是实现纳米级光操纵和等离子体科学和技术应用的核心。在这种情况下，泵浦探针光谱是研究这些集体模式和相应的能量转移过程的有力工具。在这里，我提出了石墨烯中非平衡狄拉克等离子体的第一性原理研究，其中超快条件下的阻尼通道仍未得到充分探索。激光诱导的等离子体能量蓝移可以用带内通道中电子-空穴对浓度的热增加来解释。有趣的是，虽然平衡石墨烯等离子体的阻尼路径完全由声子散射控制，光致等离子体主要将其能量转移到强耦合的热光学声子，这解释了实验观察到的等离子体线宽增加了十倍。本研究为深入理解新型二维系统和异质结构中的等离子体时间动力学铺平了道路。