Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of a New Mechanism of Spontaneous Generation of Magnetic
  Flux in a Superconductor   We report the discovery of a new mechanism of spontaneous generation of a
magnetic flux in a superconductor cooled through $T_c$. The sign of the
spontaneous flux changes randomly from one cooldown to the next, and follows a
Gaussian distribution. The width of the distribution increases with the size of
the temperature gradient in the sample. Our observations appear inconsistent
with the well known mechanisms of flux generation. The dependence on the
temperature gradient suggests that the flux may be generated through an
instability of the thermoelectric superconducting-normal quasiparticle
counterflow.

25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex