Abstract
Electron correlations play a dominant role in the charge dynamics of the cuprates. We use resonant inelastic X-ray scattering (RIXS) to track the doping dependence of the collective charge excitations in electron doped La{}_{2-x}Ce{}_{x}CuO{}_{4} (LCCO). From the resonant energy dependence and the out-of-plane momentum dependence, the charge excitations are identified as three-dimensional (3D) plasmons, which reflect the nature of the electronic structure and Coulomb repulsion on both short and long lengthscales. With increasing electron doping, the plasmon excitations increase monotonically in energy, a consequence of the electron correlation effect on electron structure near the Fermi surface (FS). Importantly, the plasmon excitations evolve from a broad feature into a well-defined peak with much increased life time, revealing the evolution of the electrons from incoherent states to coherent quasi-particles near the FS. Such evolution marks the reduction of the short-range electronic correlation, and thus the softening of the Mottness of the system with increasing electron doping.
Highlights
The electronic behavior of metals is usually described using the standard Fermi liquid theory in terms of a single-particle spectral function of well-defined electron-like quasiparticles and a twoparticle excitation spectrum dominated by long-lived collective charge excitations called plasmons.[1,2] It is, generally agreed that Fermi liquid theory breaks down in the hightemperature superconducting cuprates and the search for a fully satisfactory replacement theory remains one of the most studied problems in condensed matter physics.[3]
A key issue cuprates is limited h!aqs-spparocevedaccmesusc. hOpmtiocrael techniques are intrinsically limited to q % 0.5,6 electron energy loss spectroscopy (EELS) has no such restriction in principle, accessing c-axis dispersion remains difficult.[7,8,9,10]
We use dynamical mean field theory (DMFT) calculations to evaluate the evolution of the charge fluctuations with electron correlations
Summary
The electronic behavior of metals is usually described using the standard Fermi liquid theory in terms of a single-particle spectral function of well-defined electron-like quasiparticles and a twoparticle excitation spectrum dominated by long-lived collective charge excitations called plasmons.[1,2] It is, generally agreed that Fermi liquid theory breaks down in the hightemperature superconducting cuprates and the search for a fully satisfactory replacement theory remains one of the most studied problems in condensed matter physics.[3]. We find that a reduced effective mass and increased electronic quasiparticle coherence near the FS are the dominant effects and that electron correlations control the region of reciprocal space in which the layered electron gas model is applicable. All these effects are signs of a crossover from Mott physics to an itinerant picture, as doping drives the system from a high-temperature-superconducting to a metallic state
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