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

摘要

We study the electronic and magnetic structure of the undoped ideal two and three-leg ladder cuprates by assuming a moderate on site coulombic repulsion. This analysis is an extension of the Fermi liquids studies proposed for the CuO_2 plane in view to explain the high T_c superconductivity and the competition 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 lags, which contrasts with the predictions made from the Heisenberg model. At mean field, and for n = 3 (Sr_2Cu_3O_5), 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 gap in the static susceptibility measurements. For n = 2, we predict a gap consistent with experimental Curie susceptibility. But the expected magnetic instability is detected only in La_2Cu_2O_5, 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 superconductivity.