Phase Transitions in Staggered Spin Ladders

M. A. Martín-Delgado, R. Shankar, G. Sierra
1996 Physical Review Letters  
We map spin ladders with n l legs and couplings J 0 across all rungs and J͑1 6 g͒ along the legs, staggered in both directions, to a sigma model. Setting its u ͑2m 1 1͒p (where it is known to be gapless), we locate the critical curves in the g versus J 0 ͞J plane at each n l , and spin S. The phase diagram is rich and has some surprises: When two gapped chains are suitably coupled, the combination becomes gapless. With n l , g, and J 0 ͞J to control, the prospects for experimentally observing
more » ... y one of these equivalent transitions are enhanced. We interpret our results in the framework of the resonating valence bond description of ladders. [S0031-9007(96)01410-X] PACS numbers: 75.10.Jm, 75.30.Ds, 75.50.Ee With this paper we contribute to the explosive growth in the theoretical and experimental studies of antiferromagnetic spin chains and ladders. Recall Haldane's [1] mapping of the spin-S Heisenberg chain with Hamiltonian H J X n
doi:10.1103/physrevlett.77.3443 pmid:10062221 fatcat:qio6juii5zd7zhnnycj57e2mv4