Electronic structure of the two-legged ladder compound La1−xSrxCuO2.5

The band properties of La1−xSrxCuO2.5, an orthorhombic cuprate that contains a pair of nearly orthogonal two-legged ladders and undergoes an insulator-metal transition near x ≈ 0.2, have been calculated using the linear augmented-plane-wave method. The undoped x = 0 results feature four half-filled σ∗ bands that exhibit anisotropic (i.e., v∥v⊥ ≈ 4) rather than one-dimensional (1D) characteristics near EF. A tight-binding analysis shows that, for ladders in the x−y plane, the σ∗ bands at EF reflect a ∼50-50 O(2p)Cu(3d) admixture, with d(x2−y2) orbitals dominating (∼75%) the 3d fraction, but containing sufficient d(yz) − d(3z3−r2) hybridization (∼12%+12%) to wash out most 1D features via interladder coupling.