Snakes and Ladders

M. A. Martin-Delgado, R. Shankar, G. Sierra

We map spin ladders with $n_l$ legs and couplings $J^{\prime }$ across all rungs and $J(1\pm \gamma )$ along the legs, staggered in both directions, to a sigma model. Setting its $\theta =(2m+1)\pi$ (w…