2010/04/18:revised
2009/10/09:revised
2008/11/04:revised
2008/05/24
Paper
Preprint

Observation of Superconductivity

Yoshihiko Saito

Osaka Science Museum

Magnet floating above a superconductor. A high-temperature superconductor (HTS) is cooled in liquid nitrogen and repels a neodymium ring magnet. The horizontal movement of the magnet is controlled by a pair of chopsticks. Though it is often explained that this is the Meissner effect, this statement is not correct. Meissener effect is the phenomenon that the magnetic field lines are excluded from a superconductivity object. The repulsion of the magnet is why the magnetic field lines of the magnet are removed from the superconductor.

Let's observe the repulsion of the magnetic field lines.

The superconductor is put in this magnetic field. This magnet is a 100mm cubic neodymium magnet of mgnetic flux dencity about 0.5T at the surface.

It can be seen clearly that the magnetic field lines can not penetrate and avoid the superconductor.
Movie

It cannot be claimed that the repulsion are caused by the Meissner effect, because the repulsion by the Meissner effect can be seen up to about 10-20 mT, which is lower than the external field by the 100mm cubic neodymium magnet. The powerful repulsion is caused by the pinning effect.

If the superconductor is cooled as follows



then


the superconductor is bound to a neodymium ring magnet (the held black object) at a fixed distance for the pinned effect.
Movie1 Movie2

Let's put this superconductor above the 100mm cubic neodymium magnet.

It can be seen that the magnetic field lines of the ring-shaped neodymium magnet have been transplanted.
Movie1 Movie2 Movie3 Movie4

Let't move the HTS in in the horizontal direction.

The magnetic field lines cannot be moved in the HTS. This is the very the pinning effect.
Movie

What will happen if the superconductor is warmed in the room temperature?
Movie1 Movie2

Science Show
Magnetic Field and Superconductivity




Paper

Preprint


Acknowledgments
The author thanks Nippon Steel Corporation for supply of the superconductor.