d-wave bond-order charge excitations in electron-doped cuprates

We study charge excitation spectra in the two-dimensional t-J model on a square lattice to explore a charge-order tendency recently found in electron-doped cuprates around the carrier density 0.15. The static susceptibility of d-wave charge density, which corresponds to the nematic susceptibility at the momentum transfer q = (0, 0), shows two characteristic peaks at momenta of the form q(1) = (q', q') and q(2) = (q, 0). These two peaks originate from the so-called 2k(F) scattering processes enhanced by the d-wave character of the bond-charge density. The peak at q(1) is much broader, but develops to be very sharp in the vicinity of its instability, whereas the peak at q(2) becomes sharper with decreasing temperature, but does not diverge. The equal-time correlation function, which is measured by resonant x-ray scattering, exhibits a momentum dependence similar to the static susceptibility. We also present energy-resolved charge excitation spectra. The spectra show a V-shaped structure around q = (0, 0) and bend back toward close-to-zero energy due to the charge-order tendency at q(1) and q(2). The resulting spectra form gap-like features with a maximal gap at q approximate to q(1)/2 and q(2)/2. We discuss implications for the recent experiments in electron-doped cuprates. Copyright (C) EPLA, 2015