Spinless fermions versus spin waves in describing antiferromagnetic Heisenberg ladders

We investigate magnetic properties of the spin-1/2 two-leg Heisenberg ladder antiferromagnet developing two formulations, one of which starts from the Jordan-Wigner transformation along an elaborately ordered path, and the other of which modifies the conventional spin-wave theory so as to restore the sublattice symmetry. The static and dynamic quantities are calculated and a novel field dependence of the nuclear spin-lattice relaxation rate, which is peculiar to one-dimensional spin-gapped antiferromagnets, is pointed out in particular. (C) 2003 Elsevier B.V. All rights reserved.