Superconductivity - Part 2 of 3

At higher temperatures, a magnet is shown to rest on top of the superconducting pellet. Once the pellet is cooled sufficiently, the magnet levitates above the pellet.

A pellet of 1-2-3 yttrium barium copper oxide (YBa2Cu3O7-x) is cooled with liquid nitrogen. A magnet placed above the pellet is levitated. At a higher temperature the magnet rests on the pellet, but cooling once again causes the magnet to rise. The levitated magnet is spun with plastic tweezers.


When cooled below a "critical" temperature, some substances lose all resistance to the flow of electrical current, becoming superconductors. A current induced in a superconducting material can flow forever, providing that the temperature remains below the critical temperature. Another property of a superconductor is its interaction with a magnetic field. A magnet induces a current in the superconductor, creating a magnetic field that repels the field of the magnet. This repulsive interaction is responsible for the levitation observed in the demonstration.

It has been determined that substances with the formula YBa2Cu3O7-x behave as superconductors at relatively high temperatures (above the boiling point of liquid nitrogen). The discovery of these materials was an important breakthrough, since liquid nitrogen is cheaper and easier to handle than the liquid helium required to bring low temperature superconductors below their critical temperatures. The designation 1-2-3 refers to the relative amounts of yttrium, barium and copper in the superconductor. Note that the compound is non-stoichiometric; that is, the subscript for oxygen is not an integer (in our compound x is a little less than 0.1). Note also that the material contains a mixture of Cu2+ and Cu3+ ions.

Superconductors are already employed in instruments requiring large magnetic fields, such as nuclear magnetic resonance spectrometers. Other potential applications include resistanceless power transmission cables and levitated vehicles.

  • Design and Demonstration
    • George Lisensky Beloit College, Beloit, WI 53511
  • Text
    • George Lisensky Beloit College, Beloit, WI 53511
    • Nancy S. Gettys University of Wisconsin - Madison, Madison, WI 53706
    • David Phillips Wabash College, Crawfordsville, IN 47933
  • Video
    • Jerrold J. Jacobsen University of Wisconsin - Madison, Madison, WI 53706