Optical and acoustic plasmons in the layered material Sr_2RuO_4
arxiv(2024)
摘要
We use momentum-dependent electron energy-loss spectroscopy in transmission
to study collective charge excitations in the "strange" layer metal
Sr_2RuO_4. We cover a complete range between in-plane and out-of-plane
oscillations. Outside of 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) dispersion. Using a model for
the Coulomb interaction of the charges in a layered system, it is possible to
describe the complete range of plasmon excitations in a mean-field random phase
approximation without taking correlation effects into account. There are no
signs of over-damped plasmons predicted by holographic theories. This indicates
that long wavelength charge excitations are not influenced by local correlation
effects such as on-site Coulomb interaction and Hund's exchange interaction.
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