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arXiv:1709.09468 · Physical review. B./Physical review. B

Dual structure in the charge excitation spectrum of electron-doped cuprates

Matías Bejas, Hiroyuki Yamase, Andrés Greco

Published Dec 28, 2017• 20 citations
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Abstract

Motivated by the recent resonant x-ray scattering (RXS) and resonant inelastic x-ray scattering (RIXS) experiments for electron-doped cuprates, we study the charge excitation spectrum in a layered $t\text{\ensuremath{-}}J$ model with the long-range Coulomb interaction. We show that the spectrum is not dominated by a specific type of charge excitations, but by different kinds of charge fluctuations, and is characterized by a dual structure in the energy space. Low-energy charge excitations correspond to various types of bond-charge fluctuations driven by the exchange term ($J$ term), whereas high-energy charge excitations are due to usual on-site charge fluctuations and correspond to plasmon excitations above the particle-hole continuum. The interlayer coupling, which is frequently neglected in many theoretical studies, is particularly important to the high-energy charge excitations.

DOI
10.1103/physrevb.96.214513

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Predictions are made for the momentum- and carrier-dependent degradation of the Mott gap upon doping in high-T(c) cuprates as would be observed in Cu K-edge resonant inelastic x-ray scattering (RIXS). The two-dimensional Hubbard model with second- and third-nearest-neighbor hopping terms has been studied by numerical exact diagonalization. Special emphasis is placed on the particle-hole asymmetry of the Mott gap excitations. We argue that the Mott gap excitations observed by RIXS are significantly influenced by the interaction between charge carriers and antiferromagnetic correlations.
We study the density-density correlation function in a large-N scheme of the t-tA-J-V model.When the nearestneighbor Coulomb interaction V is zero, our model exhibits phase separation in a wide doping region and we obtain large spectral weight near momentum q ¼ ð0; 0Þ at low energy, which originates from the proximity to phase separation.These features are much stronger for electron doping than for hole doping.However, once phase separation is suppressed by including a finite V, the low-energy spectral weight around q ¼ ð0; 0Þ is substantially suppressed.Instead a sharp zero-sound mode is stabilized above the particle-hole continuum.We discuss that the presence of a moderate value of V, which is frequently neglected in the t-J model, is important to understand low-energy charge excitations especially close to q ¼ ð0; 0Þ for electron doping.This insight should be taken into account in a future study of x-ray scattering measurements.
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