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Surface vibrations, polaritons and their coupling to a 2D electron gas: interface-bound vibrations at the SrTiO3(001)
Hannes Herrmann1, Anne Oelschläger1, Wolf Widdra1
1Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, von-Danckelmann-Platz 3, 06198 Halle, Germany. wolf.widdra@physik.uni-halle.de.
None:
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 such as, e.g., high resolution electron energy loss spectroscopy (HREELS). The HREELS experiments identify all SrTiO3(001) dipole-active surface excitations, including their specific line shape and their electron-phonon coupling to a two-dimensional electron gas (2DEG). The latter is prepared by a surface reduction via annealing under ultrahigh-vacuum conditions. With formation of the 2DEG, 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 shape.
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