Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Emergent spin-$1$ Haldane gap and ferroelectricity in a frustrated
  spin-$1/2$ ladder   We report experimental and theoretical evidence that
Rb$_2$Cu$_2$Mo$_3$O$_{12}$ has a nonmagnetic tetramer ground state of a two-leg
ladder comprising antiferromagnetically coupled frustrated spin-$1/2$ chains
and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin
excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya
interaction are identified in inelastic neutron-scattering and electron spin
resonance spectra. A tiny magnetic field generates ferroelectricity without
closing the spin gap, indicating a novel class of ferroelectricity induced by a
vector spin chirality order.

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The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
37
The categories of this paper are: supr-con