Thermodynamics of the t-J Ladder: A Stable Finite Temperature Density   Matrix Renormalization Group Calculation
  Accurate numerical simulations of a doped t-J model on a two-leg ladder are presented for the particle number, chemical potential, magnetic susceptibility and entropy in the limit of large exchange coupling on the rung using a finite temperature density matrix renormalization group (TDMRG) method. This required an improved algorithm to achieve numerical stability down to low temperatures. The thermal dissociation of hole pairs and of the rung singlets are separately observed and the evolution of the hole pair binding energy and magnon spin gap with hole doping is determined. 
Beat Ammon, Matthias Troyer, T.M. Rice and N. Shibata