Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum melting of magnetic long-range order near orbital degeneracy.
  Classical phases and Gaussian fluctuations   We study the effective spin-orbital model derived for the d9 ions in a
three-dimensional perovskite lattice, as in KCuF_3, where at each site the
doubly degenerate eg orbitals contain a single hole. The model describes the
superexchange interactions that depend on the pattern of orbitals occupied. We
present the ground state properties of this model, depending on the splitting
between the eg orbitals E_z, and the Hund's rule coupling in the excited d8
states, J_H. The classical phase diagram consists of six magnetic phases which
all have different orbital ordering: two antiferromagnetic (AF) phases with
G-AF order and either x2-y2 or 3z2-r2 orbitals occupied, two phases with mixed
orbital (MO) patterns and A-AF order, and two other MO phases with either C-AF
or G-AF order. All of them become degenerate at the multicritical point
M=(E_z,J_H)=(0,0). Using a generalization of linear spin-wave theory we study
both the transverse excitations which are spin-waves and
spin-and-orbital-waves, as well as the longitudinal (orbital) excitations. The
transverse modes couple to each other, and the spin-and-orbital-wave turns into
a soft mode near the M point. Therefore, quantum corrections to the
long-range-order parameter are drastically increased near the orbital
degeneracy, and classical order is suppressed in a crossover regime between the
G-AF and A-AF phases in the (E_z,J_H) plane. This behavior is reminiscent of
that found in frustrated spin models, and we conclude that orbital degeneracy
provides a new and physically realizable mechanism which stabilizes a spin
liquid ground state due to inherent frustration of magnetic interactions. We
also point out that such a disordered magnetic phase is likely to be realized
in LiNiO_2.

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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
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The categories of this paper are: cs
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: acc-phys
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph