Large Spin Formation and Thermodynamic Properties of Disordered Spin Ladders with Site Dilution

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.