A novel basis for the study of Heisenberg spin ladders

We employ a novel plaquette basis to investigate static and dynamic properties of Heisenberg spin ladders; these materials share some of the important features of high-temperature superconductors. Insights afforded by this new basis suggest a very efficient truncation scheme for more precise calculations. When the small truncation errors are accounted for using recently developed contractor renormalization techniques, very accurate results requiring a small fraction of the computational effort of exact calculations are obtained. These methods allow us to determine the energy/site, the spin gap, and the spin response for up to 2 x 16 ladders.