Finite-size calculations of spin-lattice relaxation rates in Heisenberg   spin-ladders
  Calculations of nuclear spin-lattice relaxation rates are carried out by means of exact diagonalization on small (2 x 6) antiferromagnetic Heisenberg ladders, using the simplest forms permitted by symmetry for the hyperfine couplings for the three nuclear sites in Cu2O3 ladders. Several values of the rung/chain exchange ratio have been considered. Comparisons with experimental results, field theoretic calculations, and the Gaussian approximation highlight some open problems. 
Martin P. Gelfand (1) and Mohan Mahadevan (1) ((1) Department of   Physics, Colorado State University)