Quasiparticle bands in plane-chain coupled cuprates

The dispersion spectrum of single hole in a bilayer composed of plane and chain, each described by t-J model, coupled by t(perpendicular to)-J(perpendicular to) interactions between them, is calculated in terms of self-consistent Born approximation. It was found that for a weak interlayer coupling the two different quasiparticle bands, plane-like and chain-like bands, show a minimum at (pi/2, pi/2) and a maximum at (0, 0) or (pi, pi). In plane-like dispersion we can find an anomalous "flat" region near Fermi surface along the antiferromagnetic Brillouin zone boundary, which favors the formation of the van-Hove singularities. With increasing interlayer coupling, a large modification of the dispersions is carried out, the minimum deviates from (pi/2, pi/2) and the energy gap of the two bands decreases and finally disappears when the vertical coupling is larger enough. The shapes of the QP bands are sensitive to the vertical hopping t(perpendicular to) rather than the vertical exchange energy J(perpendicular to). As the interlayer coupling increases, the shapes of the two QP bands suggest that the chain-like band approaches to that of quasi-one dimensional model, and the plane-like band undergoes the one layer t - t'-J models' band.