  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.
