Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pseudogaps in Underdoped Cuprates   It has become clear in the past several years that the cuprates show many
unusual properties, both in the normal and superconducting states, especially
in the underdoped region. In particular, gap-like behavior is observed in
magnetic properties, c-axis conductivity and photoemission, whereas in-plane
transport properties are only slightly affected by the pseudogap. I shall argue
that these experimental evidences must be viewed in the context of the physics
of a doped Mott insulator and that they support the notion of spin charge
separation. I shall review recent theoretical developments, concentrating on
studies based on the t-J model. I shall describe a model based on quasiparticle
excitations, which predicts the doping dependence of T_c and anomalous
energy-gap-to-T_c ratios. Finally, I shall outline how the model may be derived
from a microscopic formulation of the t-J model. After a brief review of the
U(1) formulation, I shall explain some of the difficulties encountered there,
and how a new SU(2) formulation can resolve some of the difficulties.

3
The categories of this paper are: physics
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org