DMRG study of the S=1/2 Heisenberg chains with bond alternation and randomness on the strong bonds Original Research Article

The S=1/2 Heisenberg chains with bond alternation and randomness on the strong bonds are studied by the density matrix renormalization group method. It is assumed that the eventh bond is antiferromagnetic with strength J and oddth bond can take the values ±J′(J′>J>0) randomly. The ground state of this model interpolates between the Haldane phase and the dimer phase via a randomness dominated intermediate phase. From energy gap distribution and mean field treatment of the interchain coupling, we discuss the possibility of magnetic order induced by randomness in the intermediate regime. The relationship with the recent experiment for (CH3)2CHNH3Cu(ClxBr1−x)3 is also discussed.