EFFECTS OF RANDOMNESS IN GAPPED ANTIFERROMAGNETIC QUANTUM SPIN CHAINS

The effects of bond randomness are studied for spin chains with excita tion gaps in the pure case. Systems with enforced topological structur e like the spin-1/2 chain with enforced dimerization and spin-1 chain in the Haldane gapped phase appear very stable against randomness. On the other hand, systems with spontaneously generated topological order like the spin-1/2 chain with spontaneous dimerization are found to be unstable even for weak randomness despite the gap. (C) 1996 American Institute of Physics.