Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quasiparticle coherence and the nature of the metal-insulator phase
  transition in Na$_x$CoO$_2$   Layered cobaltates embody novel realizations of correlated quantum matter on
a spin-1/2 triangular lattice. We report a high-resolution systematic
photoemission study of the insulating cobaltates (Na1/2CoO2 and K1/2CoO2).
Observation of single-particle gap opening and band-folding provides direct
evidence of anisotropic particle-hole instability on the Fermi surface due to
its unique topology. Kinematic overlap of the measured Fermi surface is
observed with the $\sqrt{3}$x$\sqrt{3}$ cobalt charge-order Brillouin zone near
x=1/3 but not at x=1/2 where insulating transition is actually observed. Unlike
conventional density-waves, charge-stripes or band insulators, the on-set of
the gap depends on the quasiparticle's quantum coherence which is found to
occur well below the disorder-order symmetry breaking temperature of the
crystal (the first known example of its kind).

26
The categories of this paper are: bayes-an
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
3
The categories of this paper are: physics
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio