Spin and bond-charge excitation spectra in correlated electron systems near an antiferromagnetic phase

Magnetic and bond-charge interactions can arise from the same microscopic interaction. Motivated by this observation, we compute magnetic and bond-charge excitation spectra on an equal footing by introducing a simple effective model on a square lattice, which describes antiferromagnetic and d-wave superconducting phases around half-filling on the electron-doped side. The magnetic excitation spectrum Imχ(q,ω) has strong weight around q=(π,π) in low energy, and its intensity map exhibits a pencil-tip-like shape in q-ω space. Around q=(0,0) magnetic excitations show a steep dispersion toward the (π,π) and (π,0) directions, which is very similar to a spin-wave dispersion although the system is nonmagnetic. Bond-charge excitations are characterized by four different symmetries and studied for all possible couplings. Bond-charge fluctuations with three different symmetries have large spectral weight around q=(π,π) in a relatively low-energy region and extend widely more than the magnetic excitation spectrum. The d-wave symmetry of bond-charge excitations also has sizable spectral weight along the direction (π/2,π/2)-(0,0)-(π/2,0) in a low-energy region and exhibits softening around q≈(0.5π,0), whereas no such softening is present in the other symmetries. These results capture the essential features observed in electron-doped cuprates and may motivate an experimental test of bond-charge excitations around q=(π,π) on top of the strong magnetic excitations there as well as additional softening in the d-wave channel in the (π,π)-(π/2,π/2) region at low temperatures near the magnetic phase. We extend the present analysis to the hole-doped side and highlight a contrast to the electron-doped side, which includes incommensurate correlations, electronic nematic correlations, and spin and bond-charge resonance modes in the superconducting state.