Antiferromagnetically coupled alternating spin chains - art. no. 134408

The effect of antiferromagnetic interchain coupling in alternating spin-(1, 1/2) chains is studied by means of spin-wave theory and density-matrix reno rmalization group (DMRG). In particular, two limiting cases are investigate d, the two-leg ladder and its two-dimensional (2D) generalization. Results of the ground-state properties like energy, spin gap, magnetizations, and c orrelation functions are reported for the whole range of the interchain cou pling J(perpendicular to). For the 2D case the spin-wave results predict a smooth dimensional crossover from 1D to 2D keeping the ground state always ordered. For the ladder system, the DMRG results show that any J(perpendicu lar to) > 0 drives the system to a gapped ground state. Furthermore the beh avior of the correlation functions closely resemble the uniform spin-1/2 la dder. For J(perpendicular to) lower than 0.3, however, the gap behaves quad ratically as Delta similar to0.6J(perpendicular to)(2). Finally, it is argu ed that the behavior of the spin gap for an arbitrary number of mixed coupl ed spin chains is analogous to that of the uniform spin-1/2 chains.