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SYED: Symposium Electron-driven processes: Atomic-scale insights from theory and experiment
SYED 1: Symposium Electron-driven processes
SYED 1.3: Hauptvortrag
Donnerstag, 19. März 2020, 10:30–11:00, HSZ 01
Light MATTERs!!! — •Hrvoje Petek1, Andi Li1, Zehua Wang1, and Marcel Reutzel1,2 — 1Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA — 2Present address: I. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany
Light interacting with solid-state matter under perturbative conditions excites primarily electric dipole transitions between k-vector dependent eigenstates of the periodic lattice potentials. A time-periodic light potential, however, can modify the electronic band structure of a solid through nonperturbative interactions entangling the light-matter interaction, and opening a route to tailor material properties with light at will. I will describe two examples: 1) It will happen at zero field strength when the complex dielectric response function Re[є(ω)]∼0 and Im[є(ω)] is small. This happens for ionic solids above the longitudinal optical phonon frequency and for metals where the -є∞(ω)∼єDrude(ω), or near the interband absorption threshold. This epsilon near-zero (ENZ) response coincides with the excitation of collective ion or electron responses, i.e., in case of metals, the bulk plasmon excitation. I will describe the ENZ response of single crystalline, low-index surfaces of Ag, as measured by ultrafast multiphoton photoemission (mPP) spectroscopy. This bulk plasmonic response of Ag is fundamentally responsible for all plasmonic responses of silver, and yet the observed mPP spectra fundamentally contradict significant aspects that we expect from theory. 2) I will also report the high field response of Cu(111) surface where light is sufficiently strong to dress the electronic bands through Floquet engineering and Stark shift effects. The optical dressing opens the way to modify quasiparticles in solids at will, where, for example, electrons can be transformed into holes on subfemtosecond time scale. Our studies inform how light, electronic, and atomic degrees of freedom in solids can overcome their natural performance boundaries.