Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coexistence of Fermi arcs and Fermi pockets in a high Tc copper oxide
  superconductor   In the pseudogap state of the high-Tc copper-oxide (cuprate) superconductors,
angle-resolved photoemission (ARPES) measurements have seen an Fermi arc, i.e.,
an open-ended gapless section in the large Fermi surface, rather than a closed
loop expected of an ordinary metal. This is all the more puzzling because Fermi
pockets (small closed Fermi surface features) have been suggested from recent
quantum oscillation measurements. The Fermi arcs have worried the high-Tc
community for many years because they cannot be understood in terms of existing
theories. Theorists came up with a way out in the form of conventional Fermi
surface pockets associated with competing order, with a back side that is for
detailed reasons invisible by photoemission. Here we report ARPES measurements
of La-Bi2201 that give direct evidence of the Fermi pocket. The charge carriers
in the pocket are holes and the pockets show an unusual dependence upon doping,
namely, they exist in underdoped but not overdoped samples. A big surprise is
that these Fermi pockets appear to coexist with the Fermi arcs. This
coexistence has not been expected theoretically and the understanding of the
mysterious pseudogap state in the high-Tc cuprate superconductors will rely
critically on understanding such a new finding.

2
The categories of this paper are: math
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th