A PLANE OF WEAKLY COUPLED HEISENBERG-CHAINS - THEORETICAL ARGUMENTS AND NUMERICAL-CALCULATIONS

The S = 1/2, nearest-neighbour, quantum Heisenberg antiferromagnet on the square lattice with spatially anisotropic couplings is reconsidere d, with particular attention to the following question: at T = 0, does Neel order develop at infinitestinal interchain coupling, or is there a non-zero critical coupling? A heuristic renormalization-group argum ent is presented which suggest that previous theoretical answers to th is question are incorrect or at least incomplete, and that the answer is not universal but rather depends on the microscopic details of the model under considerations. Numerical investigations of the nearest-ne ighbour model are carried out via zero-temperature series expansions a bout Ising and dimer Hamiltonians. The results are entirely consistent with a vanishing critical interchain coupling ratio R(c); if R(c) is finite, it is unlikely to substantially exceed 0.02.