A NOVEL BASIS FOR THE STUDY OF HEISENBERG SPIN LADDERS

We employ a novel plaquette basis to investigate static and dynamic pr operties of Heisenberg spin ladders; these materials share some of the important features of high-temperature superconductors. Insights affo rded by this new basis suggest a very efficient truncation scheme for more precise calculations. When the small truncation errors are accoun ted for using recently developed contractor renormalization techniques , very accurate results requiring a small fraction of the computationa l 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.