Abstract
We map spin ladders with legs and couplings across all rungs and along the legs, staggered in both directions, to a sigma model. Setting its (where it is known to be gapless), we locate the critical curves in the versus plane at each , and spin . The phase diagram is rich and has some surprises: When two gapped chains are suitably coupled, the combination becomes gapless. With , , and to control, the prospects for experimentally observing any one of these equivalent transitions are enhanced. We interpret our results in the framework of the resonating valence bond description of ladders.
- Received 8 May 1996
DOI:https://doi.org/10.1103/PhysRevLett.77.3443
©1996 American Physical Society