Dresden 2020 – scientific programme

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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: Invited Talk

Thursday, March 19, 2020, 10:30–11:00, HSZ 01

Light MATTERs!!! — •Hrvoje Petek¹, Andi Li¹, Zehua Wang¹, and Marcel Reutzel^1,2 — 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)∼є_Drude(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.