Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Correlation between superfluid density and Tc of underdoped YBa2Cu3O6+x
  near the superconductor-insulator transition   We report measurements of the ab-plane superfluid density Ns (magnetic
penetration depth, \lambda) of severely underdoped films of YBa2Cu3O6+x, with
Tc's from 6 to 50 K. Tc is not proportional to Ns(0); instead, we find Tc ~
Ns^{1/2.3 +/- 0.4}. At the lowest dopings, Tc is as much as 5 times larger than
the upper limit set by the KTB transition temperature of individual CuO2
bilayers.

12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
18
The categories of this paper are: econ
2
The categories of this paper are: math
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th