Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phase fluctuations versus Gaussian fluctuations in optimally-doped
  YBa$_2$Cu$_3$O$_7$   We analyze recent torque measurements of the magnetization $M_d$ vs. magnetic
field $H$ in optimally doped YBa$_2$Cu$_3$O$_{7-y}$ (OPT YBCO) to argue against
a recent proposal by Rey et al that the magnetization results above $T_c$ are
consistent with Gaussian fluctuations. We find that, despite its strong
interlayer coupling, OPT YBCO displays an anomalous non-monotonic dependence of
$M_d$ on $H$ which represents direct evidence for the locking of the pair
wavefunction phase $\theta_n$ at $T_c$ and the subsequent unlocking by a
relatively weak $H$. These unusual features characterize the unusual nature of
the transition to the Meissner state in cuprate superconductors. They are
absent in low-$T_c$ superconductors to our knowledge. We also stress the
importance of the vortex liquid state, as well as the profiles of the melting
field $H_m(T)$ and the upper critical field curve $H_{c2}(T)$ in the $T$-$H$
plane. Contrary to the claims of Rey et al, we show that the curves of the
magnetization and the Nernst signal illustrate the inaccessibility of the
$H_{c2}$ line near $T_c$. The prediction of the $H_{c2}$ line by Rey et al is
shown to be invalid in OPT YBCO.

10
The categories of this paper are: q-bio
19
The categories of this paper are: eess
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys