Browsing by Author "Lubk, Axel"

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  • Item
    Open Access
    Data corresponding to the publication "Optical and acoustic plasmons in the layered material Sr2RuO4"
    (Technische Universität Dresden, 2025-03-21) Schultz, Johannes; Lubk, Axel; Jerzembeck, Fabian; Kikugawa, Naoki; Knupfer, Martin; Wolf, Daniel; Büchner, Bernd; Fink, Jörg
    We use momentum-dependent electron energy-loss spectroscopy in transmission to study collective charge excitations in the layer metal Sr2RuO4. This metal has a transition from a perfect Fermi liquid below T~30 K into a "strange" metal phase above T~800 K. We cover a complete range between in-phase and out-of-phase oscillations. Outside the classical range of electron-hole excitations, leading to a Landau damping, we observe well-defined plasmons. The optical (acoustic) plasmon due to an in-phase (out-of-phase) charge oscillation of neighbouring layers exhibits a quadratic (linear) positive dispersion. Using a model for the Coulomb interaction of the charges in a layered system, it is possible to describe the range of optical plasmon excitations at high energies in a mean-field random phase approximation without taking correlation effects into account. In contrast, resonant inelastic X-ray scattering data show at low energies an enhancement of the acoustic plasmon velocity due to correlation effects. This difference can be explained by an energy dependent effective mass which changes from ~ 3.5 at low energy to 1 at high energy near the optical plasmon energy. There are no signs of over-damped plasmons predicted by holographic theories.
  • Item
    Open Access
    Supplementary Material to "Geometry Dependent Localization of Surface Plasmons on Random Gold Nanoparticle Assemblies"
    (Technische Universität Dresden, 2025-01-13) Kalady, Mohammed Fayis; Lubk, Axel
    Assemblies of plasmonic nanoparticles (NPs) support hybridized modes of localized surface plasmons (LSPs), which delocalize in geometrically well-ordered arrangements. Here, the hybridization behavior of LSPs in geometrically completely disordered arrangements of Au NPs fabricated by an e-beam synthesis method is studied. Employing electron energy loss spectroscopy in a scanning transmission electron microscope in combination with numerical simulations, the disorder-driven spatial and spectral localization of the coupled LSP modes that depend on the NP thickness is revealed. Below 0.4nm sample thickness (flat NPs), localization increases towards higher hybridized LSP mode energies. In comparison, above 10nm thickness, a decrease of localization (an increase of delocalization) with higher mode energies is observed. In the intermediate thickness regime, a transition of the energy dependence of the localization between the two limiting cases, exhibiting a transition mode energy with minimal localization, is observed. This behavior is mainly driven by the energy and thickness dependence of the polarizability of the individual NPs.