We investigate the algebraic structure of the supersymmetric t−J model in one dimension. We prove that the Bethe ansatz states are highest-weight vectors of an spl(2,1) superalgebra. By acting with shift operators we construct a complete set of states for this model. In addition we analyse the multiplet structure of the anti-ferromagnetic ground state and some low-lying excitations. It turns out that the ground state is a member of a quartet.
Nuclear Physics B. Amsterdam. Vol. 396, no. 2/3 (May 1993), p. 611-638