Research
Interests
Time-Dependent Response of Superconducting Vortices:
Superconductors expel magnetic fields.
This famous effect is called the Meissner effect, and is the reason
why superconductors float when placed over a magnet. When
the magnetic field is strong enough, superconductivity is destroyed.
In some kinds of superconductor ("type II" superconductors),
this occurs gradually. For magnetic fields of intermediate
strength, the field penetrates through the superconductors in
narrow flux-bundles, or "vortices". They are called
vortices because electrical currents circulate around the vortex
cores much like water circulates around the core of a whirlpool
in your bathroom sink, or air circulates around the core of a
tornado.
This figure shows a numerical simulation of
the superconducting fluid around a pair of vortices. Superconductivity
is destroyed at the vortex core.
One question which has been discussed
for a long time, is how these vortices react when subjected to
an electromagnetic field (for example when you shine light on
them). Why would you do this? In physics, there are
almost never any direct ways of studying the really interesting
problems. We know that superconductivity is a property
of the electrons making up a particular material, and yet it
is not possible to look at the individual electrons themselves.
Instead, we rely on experiments which perturb the superconductor
in some way (for example, by shining light on it) and then look
at the response of thesystem. By comparing with theories
or models of the superconducting state, we learn (indirectly)
about the electrons themselves.
The major complication is that, in
an electromagnetic field, the vortices move. The electrons
no longer behave like individual electrons, but respond collectively
to the field.
Publications:
Electrodynamics of a Clean Vortex
Lattice, W. A. Atkinson and A.
H. MacDonald, Physical Review B 60, 9295--9298
(1999).
Last Modified: 08/15/01