Universality Classes of Diagonal Quantum Spin Ladders
  We find the classification of diagonal spin ladders depending on a characteristic integer $N_p$ in terms of ferrimagnetic, gapped and critical phases. We use the finite algorithm DMRG, non-linear sigma model and bosonization techniques to prove our results. We find stoichiometric contents in cuprate $CuO_2$ planes that allow for the existence of weakly interacting diagonal ladders. 
M.A. Martin-Delgado, J. Rodriguez-Laguna, G. Sierra