Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Weak-coupling calculation of the gap structure of doped n-leg Hubbard
  ladders   In weak coupling, the spin gap in doped, even, n-leg periodic Hubbard ladders
reflects the energy to break a pair into separate quasiparticles. Here we
investigate the structure of the gap within a spin-fluctuation exchange
approximation. We also calculate the amplitude for removing a singlet pair from
two lattice sites separated by a distance (l_x,l_y), which describes the
internal structure of a pair.

23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
3
The categories of this paper are: physics
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga