Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetization plateaux, Haldane-like gap, string order and hidden
  symmetry in a spin-1/2 tetrameric Heisenberg antiferromagnetic chain   The ground-state properties of a spin $S=1/2$ tetrameric Heisenberg
antiferromagnetic chain with alternating couplings AF$_{1}$-AF$_{2}$-AF$_{1}$%
-F (AF and F denote antiferromagnetic and ferromagnetic couplings,
respectively) are studied by means of the density matrix renormalization group
method. Two plateaux of magnetization $m$ are found at $m=0$ and 1/4% . It is
shown that in such a spin-1/2 AF system, there is a gap from the singlet ground
state to the triplet excited states in the absence of a magnetic field. The
spin-spin correlation function decays exponentially, and the gapped states have
a nonvanishing string order, which measures a hidden symmetry in the system. By
a dual transformation, the string order is transformed into a ferromagnetic
order and the hidden symmetry is unveiled to be a $Z_{2}\times Z_{2}$ discrete
symmetry, which is fully broken in the gapped states. This half-integer spin
Heisenberg AF chain is in a Haldane-like phase, suggesting that the present
findings extend the substance of Haldane's scenario. A valence-bond-solid state
picture is also proposed for the gapped states.

20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th