Exact solution of an S=1/2 Heisenberg antiferromagnetic chain with long-ranged interactions.

The S=½ Heisenberg Hamiltonian H = ½ N - 1Σn = 1NΣm = 1 Jn σM · σm+n with Jn=J0/sin2 (nπ/N), is shown to have a simple singlet ground state in the form of a Jastrow function. The spectrum and correlations are explicitly known and the magnetic susceptibility is shown to be Pauli type at T=0. The model has a striking similarity to the nearest-neighbor isotropic Heisenberg model and may be viewed as a discretized version of the Sutherland-Calogero-Moser system.