Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Snakes and Ladders   We map spin ladders with $n_l$ legs and couplings $J'$ across all rungs and
$J(1 \pm \gamma)$ along the legs, staggered in both directions, to a sigma
model. Setting its $\theta = (2m+1)\pi$ (where it is known to be gapless), we
locate the critical curves in the $\gamma$ versus ${J'\over J}$ 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,
\gamma $ and $J'/J$ to control, the prospects for experimentally observing any
one of these equivalent transitions seem bright. We discuss the order
parameters and the behavior of holes in the RVB description.

18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
0
The categories of this paper are: hep-ph