Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Bilayer Kitaev models: Phase diagrams and novel phases   Kitaev's honeycomb-lattice spin-$1/2$ model has become a paradigmatic example
for $\mathbb{Z}_2$ quantum spin liquids, both gapped and gapless. Here we study
the fate of these spin-liquid phases in differently stacked bilayer versions of
the Kitaev model. Increasing the ratio between the inter-layer Heisenberg
coupling $J_\perp$ and the intra-layer Kitaev couplings $K^{x,y,z}$ destroys
the topological spin liquid in favor of a paramagnetic dimer phase. We study
phase diagrams as a function of $J_\perp/K$ and Kitaev coupling anisotropies
using Majorana-fermion mean-field theory, and we employ different expansion
techniques in the limits of small and large $J_\perp/K$. For strongly
anisotropic Kitaev couplings, we derive effective models for the different
layer stackings which we use to discuss the quantum phase transition out of the
Kitaev phase. We find that the phase diagrams depend sensitively on the nature
of the stacking and anisotropy strength. While in some stackings and at strong
anisotropies we find a single transition between the Kitaev and dimer phases,
other stackings are more involved: Most importantly, we prove the existence of
two novel macro-spin phases which can be understood in terms of Ising chains
which can be either coupled ferromagnetically or remain degenerate, thus
realizing a classical spin liquid. In addition, our results suggest the
existence of a flux phase with spontaneous inter-layer coherence.

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The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
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The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
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The categories of this paper are: nlin
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The categories of this paper are: hep-lat
3
The categories of this paper are: physics