Electronic and magnetic structure of the undoped two and three-leg ladder cuprates in an itinerant electrons model

We study the electronic and magnetic structure of the undoped ideal two and three-leg ladder cuprates by assuming a moderate on site coulombic repulsi on. This analysis is an extension of the Fermi liquids studies proposed for the CuO2 plane in view to explain the high T-c superconductivity and the c ompetition with the antiferromagnetic phase. At zero doping, the quasi-one- dimensionality of the structure results in SDW correlations with different (commensurate) vectors according to the number of legs, which contrasts wit h the predictions made from the Heisenberg model. At mean field, and for n = 3 (Sr2Cu3O5), we predict a magnetic ordered state, detected by mu Sr and NMR measurements with critical temperatures consistent with our assumptions on the physical parameters, the modulation vector being pi/2. The presence of several bands at the Fermi level explains why there is no observable ga p in the static susceptibility measurements. For n = 2, we predict a gap co nsistent with experimental Curie susceptibility. But the expected magnetic instability is detected only in La2Cu2O5, where the interladder coupling is stronger. In every case the one-dimensional van Hove singularities are far from the Fermi level, making difficult the obtaining of high T-c supercond uctivity.