Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pinning effects on flux flow instability in epitaxial Nb thin films   The flux flow properties of epitaxial niobium films with different pinning
strengths are investigated by dc electrical resistance measurements and mapped
to results derived within the framework of a theoretical model. Investigated
are the cases of weak random pinning in as-grown films, strong random pinning
in Ga ion-irradiated films, and strong periodic pinning induced by a nanogroove
array milled by focused ion beam. The generic feature of the current-voltage
curves of the films consists in instability jumps to the normal state at some
instability current density $j^\ast$ as the vortex lattice reaches its critical
velocity $v^\ast$. While $v^\ast(B)$ monotonically decreases for as-grown
films, the irradiated films exhibit a non-monotonic dependence $v^\ast(B)$
attaining a maximum in the low-field range. In the case of nanopatterned films,
this broad maximum is accompanied by a much sharper maximum in both,
$v^\ast(B)$ and $j^\ast(B)$, which we attribute to the commensurability effect
when the spacing between the vortex rows coincides with the location of the
grooves. We argue that the observed behavior of $v^\ast(B)$ can be explained by
the pinning effect on the vortex flow instability and support our claims by
fitting the experimental data to theoretical expressions derived within a model
accounting for the field dependence of the depinning current density.

0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas