Researchers
studying a superconducting strip observed an intermittent motion of
magnetic flux which carries vortices inside the regularly spaced weak
conducting regions carved into the superconducting material. These
vortices resulted in alternating static phases with zero voltage and
dynamic phases, which are characterised by non-zero voltage peaks in the
superconductor. This study, which is about to be published in EPJ B¹,
was carried out by scientists from the Condensed Matter Theory Group of
the University of Antwerp, Belgium, working in collaboration with
Brazilian colleagues.
Superconductors,
when subjected to sufficiently strong magnetic fields, feature vortices
that carry quantized amounts of magnetic flux, although the natural
tendency of superconductors is to expel such flux. The authors relied on
the Ginzburg-Landau theory to study the dynamic of the nanometric- to
millimetric-scale-width superconducting strip, which was subjected to a
magnetic field applied at a right angle and a current applied alongside
its length.
Typically,
weakly acting superconducting regions are natural impediments for the
passage of electrical current. However, the authors found that they also
work as efficient pathways for vortices to enter and exit the
superconducting strip. The increasing magnetic field also increases the
density of mutually repelling vortices, which stimulates vortex motion
across the strip in the presence of an external current. At the same
time, the barrier for vortex entry and exit on the strip boundaries is
also dependent on the magnetic field. This interplay of
magnetic-field-dependent barriers and vortex-vortex interaction results
in an on/off vortex motion in increasing magnetic fields.
Due
to the simple geometry of the strip, these results can be confirmed
experimentally in magnetoresistance measurements. These findings could
be applicable in gate devices used to control various modes of on/off
states in electrical systems which operate in specific windows of
temperature, applied magnetic field, current and voltage.
Source: Springer
