Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum effects in a weakly-frustrated S=1/2 two-dimensional Heisenberg
  antiferromagnet in an applied magnetic field   We have studied the two-dimensional S=1/2 square-lattice antiferromagnet
$Cu(pz)_2(ClO_4)_2$ using inelastic neutron scattering and series expansion
calculations. We show that the presence of antiferromagnetic next-nearest
neighbor interactions enhances quantum fluctuations associated with resonating
valence bonds. Intermediate magnetic fields lead to a selective tuning of
resonating valence bonds and a spectacular inversion of the zone-boundary
dispersion, providing novel insight into 2D antiferromagnetism in the quantum
limit.

37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org