University of Pittsburgh

报告人简介：

Prof. Hrvoje Petek obtained BS degree (1980) form MIT, and PhD degree (1985) from the University of California Berkeley both in chemistry. He worked with Keitaro Yoshihara as the National and Yamada Science Foundations postdoctoral fellow and Research Associate at the Institute of Molecular Science, Japan (1985-1992). He was a Senior Research Scientist at the Hitachi Advanced Research Laboratory (1993-2000), where he initiated research on ultrafast electron dynamics in the solid state. He is continuing this research as a Professor of Physics and RK Mellon Chair of Physics and Astronomy since 2000. Petek has been recognized with the Alexander von Humboldt Research Award (2000), Morino Award (2014), Ahmed Zewail Award in Ultrafast Science and Technology (2019), and as distinguished Scientist of the Chinese Academy of Sciences (2022). He is a Fellow of the American Physical Society, and American Academy of Arts and Sciences, the Editor-in-Chief of Progress in Surface Science, and a member of numerous advisory boards.

报告摘要：

When illuminated by light, free electrons in a metal screen the applied optical field by inducing the screening charge density on the Fermi screening length scale. We consider the screening charge density to consist of free electrons that are dressed by the optical field. They are often described by a theoretical cartoon but never quantitatively examined in the process of screening. We perform two photon photoemission spectroscopy as a function of the optical field strength on attosecond time scale projecting the coherently dressed electrons into the photoemission continuum for electron energy, momentum, and time analysis.1 The photoemission spectra of silver in the near-UV region show a field strength-dependent transformation from Bloch bands to a delocalized electron distribution that has lost character of the single particle band structure of silver. The optical field appears to induce a phase transition from a lattice-periodic band structure to a correlated photon-electron state. Interferometric measurements show that the optical field dressed state appears and decays on sub-optical cycle, attosecond time scale. Spectroscopic evidence shows a significant role of the A2 ponderomotive/diamagnetic response of the electronic system, where A is the electromagnetic vector potential.

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邀请人：孟胜（8264 9396）

联系人：胡颖（8264 9361）