Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vanishing of phase coherence in underdoped Bi_2Sr_2CaCu_2O_8+d   Coherent time-domain spectroscopy is used to measure the screening and
dissipation of high-frequency electromagnetic fields in a set of underdoped
Bi_2Sr_2CaCu_2O_8+d thin films. The measurements provide direct evidence for a
phase-fluctuation driven transition from the superconductor to normal state,
with dynamics described well by the Berezinskii-Kosterlitz-Thouless theory of
vortex-pair unbinding.

6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
24
The categories of this paper are: dg-ga