Optical and acoustic plasmons in the layered material Sr${}_2$RuO${}_4$

Abstract

We use momentum-dependent electron energy-loss spectroscopy in transmission to study collective charge excitations in the layer metal Sr${}_2$RuO${}_4$. This metal has a transition from a perfect Fermi liquid below $T\approx 30$K into a "strange" metal phase above $T\approx 800$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 $\approx$ 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.

References in corpus (22)

• Janus-faced influence of the Hund's rule coupling in strongly correlated materials
• Universality of the Mott-Ioffe-Regel limit in metals
• Fermi Surface, Surface States, and Surface Reconstruction in Sr2RuO4
• How bad metals turn good: spectroscopic signatures of resilient quasiparticles
• The Electronic Nature of High Temperature Cuprate Superconductors
• Planckian dissipation, minimal viscosity and the transport in cuprate strange metals
• Three dimensional collective charge excitations in electron-doped cuprate superconductors
• Anomalous density fluctuations in a strange metal
• Photoemission Quasi-Particle Spectra of Sr${}_2$RuO${}_4$
• Detection of Acoustic Plasmons in Hole-Doped Lanthanum and Bismuth Cuprate Superconductors Using Resonant Inelastic X-Ray Scattering
• Optical Response of Sr${}_2$RuO${}_4$ Reveals Universal Fermi-liquid Scaling and Quasiparticles Beyond Landau Theory
• Theory of the density fluctuation spectrum of strongly correlated electrons
• Plasmon excitations in layered high-Tc cuprates
• Acoustic plasmons and conducting carriers in hole-doped cuprate superconductors
• Improved Single-Crystal Growth of Sr${}_2$RuO${}_4$
• Anomalous attenuation of plasmons in strange metals and holography
• Gapped collective charge excitations and interlayer hopping in cuprate superconductors
• On the engineering of higher-order Van Hove singularities in two dimensions
• The fate of quasiparticles at high-temperature
• Impact of electron correlations on two-particle charge response in electron- and hole-doped cuprates
• Propagating charge carrier plasmon in Sr2RuO4
• Evidence for an orbital dependent Mott transition in the ladders of (La,Ca)${}_x$Sr${}_{14-x}$Cu${}_{24}$O${}_{41}$ derived by electron energy-loss spectroscopy