Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Bond ordering and phase transitions in Na$_{2}$IrO$_{3}$ under high
  pressure   The Kitaev model of spin-1/2 on a honeycomb lattice supports degenerate
topological ground states and may be useful in topological quantum computation.
Na$_{2}$IrO$_{3}$ with honeycomb lattice of Ir ions have been extensively
studied as candidates for the realization of the this model, due to the
effective $J_{\text{eff}}=1/2$ low-energy excitations produced by spin-orbit
and crystal-field effect. As the eventual realization of Kitaev model has
remained evasive, it is highly desirable and challenging to tune the candidate
materials toward such end. It is well known external pressure often leads to
dramatic changes to the geometric and electronic structure of materials. In
this work, the high pressure phase diagram of Na$_{2}$IrO$_{3}$ is examined by
first-principles calculations. It is found that Na$_{2}$IrO$_{3}$ undergoes a
sequence of structural and magnetic phase transitions, from the magnetically
ordered phase with space group $C2/m$ to two bond-ordered non-magnetic phases.
The low-energy excitations in these high-pressure phases can be well described
by the $J_{\text{eff}}=1/2$ states.

8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex