Quasiparticle bands in plane-chain coupled cuprates

The dispersion spectrum of single hole in a bilayer composed of plane and c hain, each described by t-J model, coupled by t(perpendicular to)-J(perpend icular to) interactions between them, is calculated in terms of self-consis tent Born approximation. It was found that for a weak interlayer coupling t he 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-li ke dispersion we can find an anomalous "flat" region near Fermi surface alo ng the antiferromagnetic Brillouin zone boundary, which favors the formatio n of the van-Hove singularities. With increasing interlayer coupling, a lar ge modification of the dispersions is carried out, the minimum deviates fro m (pi/2, pi/2) and the energy gap of the two bands decreases and finally di sappears 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 coupli ng increases, the shapes of the two QP bands suggest that the chain-like ba nd approaches to that of quasi-one dimensional model, and the plane-like ba nd undergoes the one layer t - t'-J models' band.