Nonlocal excitations and 1/8 singularity in cuprates

Abstract

Momentum-dependent excitation spectra of the two-dimensional Hubbard model on a square lattice have been investigated at zero temperature on the basis of the full self-consistent projection operator method in order to clarify nonlocal effects of electron correlations on the spectra. Intersite antiferromagnetic correlations are found to cause shadow bands and enhance the Mott-Hubbard splittings near the half-filling. Furthermore, nonlocal excitations are shown to move the critical doping concentration δ h *, at which the singular quasiparticle peak is located just on the Fermi level, from δ h * = 0.153 (the single-site value) to δ h * = 0.123. The latter suggests the occurrence of an instability such as the stripe at δ h * = 1/8.