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

Abstract

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 dwave charge density, which corresponds to the nematic susceptibility at the momentum transfer q = (0, 0), shows two characteristic peaks at momenta of the form q1 = (q ′ , q ′ ) and q2 = (q, 0). These two peaks originate from the socalled 2kF scattering processes enhanced by the d-wave character of the bond-charge density. The peak at q1 is much broader, but develops to be very sharp in the vicinity of its instability, whereas the peak at q2 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 q1 and q2. The resulting spectra form gap-like features with a maximal gap at q ≈ q1/2 and q2/2. We discuss implications for the recent experiments in electron-doped cuprates.

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

“…This subleading mode may correspond to the CO features observed in RXS experiments 15 , as was discussed in Ref. 27; see also Sec. III E and Sec.…”

“…28 by employing a model different from that in Ref. 27. On the other hand, high-energy spectrum revealed a quasi-linear dispersive mode around q = (0, 0) with an energy gap about 300 meV (Ref.…”

“…In Ref. 27 it was discussed that the observed shortrange CO is a d-wave bond order and its modulation vector is determined by 2k F scattering processes that connect the two Fermi momenta on the boundary of the Brillouin zone (BZ).…”

“…However, more work would be necessary before reaching such a conclusion. First, the CO was studied in the two-dimensional (2D) t-J model 27,31 , whereas the high-energy mode was analyzed in the layered t-J-V model 29 , with V being the long range Coulomb interaction. Thus, it is not clear whether the obtained insight about the CO in the 2D t-J model remains valid also in a more realistic model such as the layered t-J-V model.…”

Charge-Density-Excitation Spectrum in the t–t′–J–V Model

“…showed that the present large-N framework can capture short-range charge order recently observed by resonant x-ray scattering 13,21 and also a mysterious mode around q = (0, 0)…”