ELECTRONIC STRUCTURE OF LADDER CUPRATES

We study the electronic structure of the ladder compounds SrCu 2 O 3 and Sr 14-x Ca x Cu 24 O 41 . Our local-density approximation calculations for SrCu2O3 give similar Cu 3d bands near the Fermi energy as reported for Sr 14-x Ca x Cu 24 O 41 . The hopping parameters estimated by fitting these bands show a strong anisotropy between the t ⊥ and t ‖ intraladder hopping and small interladder hopping. A downfolding method shows that this anisotropy arises from the ladder structure. The conductivity perpendicular to the ladders is computed assuming incoherent tunneling giving a value close to experiment.