Abstract :

One of the defining properties of metals is the ability to reflect light with nearly perfect efficiency and fidelity from clean, polished metal surfaces. This property has made metallic mirrors an essential and valued accessory as well as the first optical instrument in daily use for more than 5000 years. As most budding physicists learn, the canonical description of reflection of light is given by Maxwell's equations; they describe the response of free electrons in a metal to an external field in terms of perfect screening of the electromagnetic field and consequent induced currents, which regenerate the field in the form of coherent reflection. Yet the microscopic description of the quantum mechanical interaction of light quanta, photons, with metals has been hardly explored. In this talk I will present the latest results on the coherent light-metal surface interactions probed by multi-photon multidimensional photoemission spectroscopy. A femtosecond laser pulse with ~2 eV photon energy excites electrons from a surface state below the Fermi level of single crystal Ag(111) surface by several quanta to an energy level above the vacuum potential, where it is emitted into the vacuum. The analysis of photoelectron distribution with respect to energy and momentum reveals features that are characteristic of an exciton, a quasiparticle not yet observed in metals. Further analysis with respect to time reveals the dynamics of this transient excitonic state, which is intimately responsible for the coherent response of metals.

ABOUT THE SPEAKER :

Hrvoje Petek is the R. K. Mellon Chair of Physics and Astronomy and Professor of Chemistry at the University of Pittsburgh. He vas born in Yugoslavia and at 11 emigrated the USA. He received his degrees in Chemistry from MIT (BS; 1980) and U.C. Berkeley (PhD; 1985). From 1985 to 1993 he was first a postdoctoral fellow and then a Research Associate at the Institute for Molecular Science in Okazaki, Japan. In 1993 he joined the Hitachi Advanced Research Laboratory as a Group Leader. There he initiated his current research on ultrafast electronic spectroscopy, microscopy, and dynamics of solids and solid surfaces. From 2000 he joined the University of Pittsburgh as a Professor of Physics. He has received various Awards including the Alexander von Humboldt Award, Chancellor's Distinguished Research Awards, American Physical Society Fellowship, Morino Award, and others. Since 2006 he has been the Editor-in-Chief of Progress in Surface Science