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Project E5: Time-resolved spectroscopy of photo-induced transitions and electronic excitations in quasi-1D metal wires on semiconductors

Manuel Ligges, Ralph Ernstorfer, Uwe Bovensiepen, Martin Wolf

Our project aims at understanding the ultrafast dynamics of elementary scattering processes and photoinduced transitions in quasi-1D metallic wires on semiconductor surfaces. We will study the dynamics of electron-electron and electron-phonon scattering as well as the time-dependent evolution of the electronic band structure after optical excitation using femtosecond time- and angle-resolved photoemission spectroscopy (trARPES) and twophoton photoelectron spectroscopy (tr2PPE). Our femtosecond time- and momentumresolved studies complement the corresponding experimental projects using (static) photoemission in thermal equilibrium, optical, and transports methods as well as the theoretical projects. Time-resolved experiments will be first performed on the established, prototypical material systems of In/Si(111) and Pb/Si(557) to establish and test the connection between the dynamical properties probed in this project in the time domain to transport and optical properties also analyzed within the Research Unit. Subsequently we aim at analyzing Au, Pt, and Silicide wires. The goals of the project are as follows: (i) Determination of the unoccupied electronic band structure, providing a benchmark for theory. (ii) Analysis of the ultrafast momentum-dependent population dynamics in unoccupied bands. These are expected to present a pronounced anisotropy depending on the momentum change parallel or perpendicular to the chain direction. (iii) Investigation of the non-adiabatic energy relaxation to gain insight into the anisotropy of electron-phonon mediated relaxation processes and the coupling of electronic states and coherently excited phonon modes. Such analysis requires knowledge of the adiabatic temperature and doping dependence of metal-insulator transitions, which we will obtain from temperature-dependent static ARPES.

(Panels (E) to (I) show the momentum-dependent
dynamics of the CDW melting in TbTe3)