Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum critical behaviour in the superfluid density of strongly
  underdoped ultrathin cuprate films   A central issue in the physics of high temperature superconductors is to
understand superconductivity within a single copper-oxide layer or bilayer, the
fundamental structural unit in the cuprates, and how it is lost with
underdoping. As mobile holes are removed from the CuO_2 planes, the transition
temperature T_C and superfluid density n_S decrease in a surprisingly
correlated fashion in crystals and thick films. We seek to elucidate the
intrinsic physics of bilayers in the strongly underdoped regime, near the
critical doping level where superconductivity disappears. We report
measurements of n_S(T) in films of Y_{1-x}Ca_xBa_2Cu_3O_{7-\delta} as thin as
two copper-oxide bilayers with T_C's as low as 3 K. In addition to seeing the
two-dimensional (2D) Kosterlitz-Thouless-Berezinski transition at T_C, we
observe a remarkable scaling of T_C with n_S(0) that demonstrates that the
disappearance of superconductivity with underdoping is due to quantum
fluctuations near a T = 0 2D quantum critical point.

8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math