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O: Fachverband Oberflächenphysik
O 23: Ultrafast Electron Dynamics at Surfaces and Interfaces III
O 23.4: Talk
Tuesday, March 19, 2024, 11:15–11:30, MA 041
Nonperturbative Floquet-Landau-Zener Mechanism in Multiphoton Photoemission on Metal Surface — •Yun Yen1,2, Marcel Reutzel3, Andi Li4, Hrvoje Petek4, and Michael Schüler1,5 — 1Laboratory for Materials Simulations, Paul Scherrer Institute, Villigen PSI, Switzerland — 2Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland — 3Physikalisches Institut, Georg-August-Universitat Gottingen, Gottingen, Germany — 4Department of Physics and Astronomy and Pittsburgh Quantum Institute, University of Pittsburgh, Pittsburgh, Pennsylvania, USA — 5Department of Physics, University of Fribourg, Fribourg, Switzerland
In the Floquet engineering picture, time periodic optical fields perturbatively replicate states shifted by photon energy quanta, and cause field-dependent Autler-Townes splitting. As the field intensifies, light matter interaction shows more non-perturbative nature. Here we reveal the onset of non-perturbative responses in multiphoton photoemission (mPP) process for a driven two-level system of Cu(111) surface states. With strong enough driving, Floquet side bands form avoided crossing gaps, and thus lead to Landau-Zener (LZ) non-adiabatic tunneling within subcycle time scale. We further simulate the population dynamics with instantaneous Floquet state (IFS) formalism, and successfully reproduce experimental mPP features. Interpretation of the mPP process by Floquet-LZ theory elaborates the importance of non-adiabatic dynamics in strong field regime.
Keywords: Floquet; Photoemission; Landau-Zener; Strong field; light-matter interaction