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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 30: SrTiO₃: A Versatile Material from Bulk Quantum Paraelectric to 2D Superconductor III (joint session TT/KFM/MA/O)

KFM 30.3: Talk

Friday, March 22, 2024, 10:00–10:15, H 0104

Low-energy excitations at SrTiO₃(001) surfaces in absence and presence of a two-dimensional electron gas — •Hannes Herrmann, Anne Oelschläger, and Wolf Widdra — Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany

The low-energy excitations of SrTiO₃, a large-bandgap oxide perovskite, are dominated by phonons and phonon polaritons. At the surface they couple to dipole-active surface phonon polaritons that are bound to the SrTiO₃-vacuum interface. These excitations can be addressed by surface vibrational spectroscopy techniques as, e.g., high-resolution electron energy loss spectroscopy (HREELS).
Here we will present HREELS studies that identify all SrTiO₃(001) dipole-active excitations, including their specific line shapes and will discuss the electron-phonon coupling to a two-dimensional electron gas. The latter are prepared with variable charge-carrier concentrations either by annealing under ultrahigh-vacuum condition or by growth of an ultrathin layers of EuO on top. With formation of the 2DEGs, the discrete surface phonon polaritons couple to the electron-hole pair continuum as is witnessed by a substantial line broadening and asymmetric Fano-like line shapes. A quantitative description that accounts for all details of the line shape paves the way for an in-situ analysis of the 2DEG charge carrier dynamics.

Keywords: SrTiO3; phonons; HREELS; Oxide surfaces; electronic structure