What is Superconductivity?
Superconductivity is a phenomenon displayed by some materials when they
are cooled below a certain temperature, known as the superconducting
critical temperature, Tc.
Below Tc, superconducting
materials exhibit two characteristic properties:
Zero electrical resistance means that no energy is lost as heat as the
material conducts electricity - this has many applications, which you
can read about in the Uses section.
The second of these properties, perfect diamagnetism,
means that the superconducting material will exclude a magnetic field
- this is known as the Meissner effect (after its discoverer), and can
be used to display extraordinary physical effects:
Left: The Meissner effect is used to levitate a superconductor
above a magnet. To re-create this effect yourselves, see Making
your own superconductors.
(Click on the image to see a QuickTime movie
of the Meissner effect - Download Apple's QuickTime plugin from
if you do not already have it)
Superconducting materials can be categorised into
one of two types:
Type I Superconductors - which totally exclude all applied
magnetic fields. Most elemental superconductors are Type I.
Type II Superconductors - which totally exclude low applied
magnetic fields, but only partially exclude high applied magnetic
fields; their diagmagnetism is not perfect but mixed in the presence
of high fields. Niobium is an example of an elemental Type II superconductor.
Both types exhibit perfect electrical conductivity, and can be restored
to 'normal' conductors in the presence of a sufficiently strong magnetic
For further information about Type I and Type II superconductivity, you
might like to look at the relevant section at Superconductor.org
- Type I or Type
To learn why superconductors exhibit these extraordinary properties,
go to the Theory section.