Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nodes in the gap structure of the iron-arsenide superconductor
  Ba(Fe_{1-x}Co_x)_2As_2 from c-axis heat transport measurements   The thermal conductivity k of the iron-arsenide superconductor
Ba(Fe_{1-x}Co_x)_2As_2 was measured down to 50 mK for a heat current parallel
(k_c) and perpendicular (k_a) to the tetragonal c axis, for seven Co
concentrations from underdoped to overdoped regions of the phase diagram (0.038
< x < 0.127). A residual linear term k_c0/T is observed in the T = 0 limit when
the current is along the c axis, revealing the presence of nodes in the gap.
Because the nodes appear as x moves away from the concentration of maximal T_c,
they must be accidental, not imposed by symmetry, and are therefore compatible
with an s_{+/-} state, for example. The fact that the in-plane residual linear
term k_a0/T is negligible at all x implies that the nodes are located in
regions of the Fermi surface that contribute strongly to c-axis conduction and
very little to in-plane conduction. Application of a moderate magnetic field
(e.g. H_c2/4) excites quasiparticles that conduct heat along the a axis just as
well as the nodal quasiparticles conduct along the c axis. This shows that the
gap must be very small (but non-zero) in regions of the Fermi surface which
contribute significantly to in-plane conduction. These findings can be
understood in terms of a strong k dependence of the gap Delta(k) which produces
nodes on a Fermi surface sheet with pronounced c-axis dispersion and deep
minima on the remaining, quasi-two-dimensional sheets.

12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph