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Researchers create conveyer belt
for magnetic flux vortices in superconductors
If blown up in size, it would not have a chance in
the car factory, but the microscopic conveyer belt built by
Simon Bending's team in the Department of Physics at the
University of Bath and
collaborators in Japan and the USA, could just be the next big thing for
improving devices relying on the elusive properties of superconductors (Nature
Materials, Advanced Online Publication March 12 2006). It's not your standard
rubber band on cylinders though – it moves in an erratic way, a quick jolt to
the left, a smooth slide to the right. Who would want to be on such a thing?
Tiny swirls of electric currents, it seems. These
so-called vortices are the closest things to 'hurricanes' for the
superconducting researcher and engineer, and no less threatening. That's because
the zero resistance to current flow in even the best superconductors breaks down
once vortices enter and start to move around. Their motion can also lead to
unpredictable 'noise' if it takes place near the most sensitive regions of
superconducting devices. Bending has now shown that it is possible to move
vortices around inside a superconductor almost at will using his shaky conveyer
belt. In this way they can either be removed entirely or at least left where
they cause the least harm.
The asymmetry in its movement is the key to
success, since it ensures that the vortices all move in one direction, even
though the belt itself moves back and forth. The reason behind this is that the
vortices can only follow along during the smooth slides to the right, and not
during the jolts in the other direction. The conveyer belt thus acts in some
sense as a rectifier, just like the diodes known from electronics.
The mind-boggling part is now that the conveyer
belt is assembled out of a line of vortices itself, created and controlled by a
time-varying magnetic field. As the researchers show, this way "bad" vortices
can be completely removed out of targeted regions inside the superconductor, and
the vortices induced to create the conveyer belt can be readily removed from the
sample afterwards if need be.
Using this trick, superconducting devices, such
as filters for telecommunications or ultra-sensitive magnetic field probes,
could be improved by removing vortices - naturally caused by the earth's
magnetic field or man-made disturbances – from regions critical to device
operation.
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