Heisenberg spin chains with four-spin couplings

Mustansir Barma

Z. Song

Martin Reigrotzki, Hirokazu Tsunetsugu, Thomas Maurice Rice

The properties of antiferromagnetic Heisenberg S= 1/2 ladders with two, three and four chains are expanded in the ratio of the intrachain and interchain coupling constants. A simple mapping procedure is introduced to relate the four- and two-chain ladders, which keeps to moderate values of the expansion parameters. A second-order calculation of the spin gap to the lowest triplet excitation in the two- and four-chain ladders is found to be quite accurate, even at the isotropic point where the couplings are equal. Similar expansions and mapping procedures are presented for the three-chain ladders, which are in the same universality class as single chains.

Ute L ow

Holger Frahm, Claus Rödenbeck

We show that the solutions of the Yang-Baxter equation invariant under the action of the Yangian Y ( sl 2 ) lead to inhomogeneous vertex models. Starting from a four-dimensional representation of Y ( sl 2 ), we obtain an integrable family of coupled Heisenberg spin-½ chains. Some thermodynamical properties of this model are studied by means of the algebraic Bethe ansatz.

Adriana Moreo