Magnetization Plateaux in Bethe Ansatz Solvable Spin-S Ladders

We examine the properties of the Bethe ansatz solvable two- and three-leg spin-S ladders. These models include Heisenberg rung interactions of arbitrary strength and thus capture the physics of the spin-S Heisenberg ladders for strong rung coupling. The discrete values derived for the magnetization plateaux are seen to fit with the general prediction based on the Lieb-Schultz-Mattis theorem. We examine the magnetic phase diagram of the spin-1 ladder in detail and find an extended magnetization plateau at the fractional value 〈M〉 = 1/2 in agreement with the experimental observation for the organic polyradical spin-1 ladder compound BIP-TENO