  Low temperature properties of antiferromagnetic two-leg spin-1/2 ladders with
bond randomness and site dilution (or doping with nonmagnetic impurities) are
studied using the real-space renormalization-group technique. We find that for
non zero doping concentrations the systems are driven into a phase dominated by
large effective spins, i.e. the Large Spin phase. The susceptibility follows a
universal Curie-like 1/T behavior at low temperature,regardless of the doping
concentrations (as long as it is nonzero) and the strength of bond randomness.
Very similar behavior has been found in ladders that are doped with magnetic
impurities that carry spin-1.
