报 告 人：Sheng Meng, Institute of Physics, Chinese Academy of Sciences

报告地点：物理楼W101报告厅

内容摘要：Photoexcitation and the resultant attosecond quasiparticle dynamics is a powerful means in distinguishing different interactions and manipulating the states of matter, especially in complex quantum materials, thus giving rise to a new focused area of “attosecond condensed matter physics”. Here we give some examples of such a field by investigating photoexcitation-induced correlated electron-lattice dynamics at the attosecond timescale with the recently developed new theoretical tools incorporating both nonadiabatic electron-nuclear couplings and nuclear quantum effects. In particular, we uncover the attosecond ultrafast processes of exciton formation, evolution and dissociation in monolayer hexagonal boron nitride, and the subsequent exciton-exciton interference phenomenon, where the resulting oscillatory signals of electron occupation allow us to extract phase information of exciton envelope function. Another example is the attosecond process of high harmonics generation (HHG) in solids. The lack of consideration for couplings between HHG and other quasiparticles, such as phonons, impedes our understanding of many-body interactions in HHG. Coherent phonons are revealed to effectively affect HHG via the adiabatic band modulation induced by phonon deformation effects and the nonadiabatic nonequilibrium distribution of photocarriers in multiple valleys. The adiabatic and nonadiabatic mechanisms leave their fingerprint via influencing the phonon period and phase delay in the oscillation of HHG intensity, both of which are experimentally measurable. Investigation of these quantities enables the direct probing of the exciton-exciton and electron-phonon interactions in materials.