Lecture 1 : Historical review and a survey of properties of superconductors.
Historical Overview
Superconductivity is an exciting area of physics where truly exotic phenomena can now be demonstrated with relatively inexpensive instruments/equipment. One of the most appealing demnstrations is that of a superconductor moving on magnetic rails in a levitated fashion thereby suggesting futuristic applications.
The video demonstrates some astonishing properties of superconductors. The
black cylindrical pellet is the high-Tc superconductor YBa2Cu3O7 which has a Tc of
about 90K. This pellet forms the bottom of a hollow cylinder of teflon shown
in the video. The shiny rectangular piece is a Nd-Fe-B permanent magnet
which has been magnetised in a direction perpendicular to the bar (unlike a
standard bar magnet). When the superconductor is at room temperature
(about 300K), there is nothing special about it. When it is placed on the
magnet, it just sits on it and the magnetic field penetrates it. When the
superconductor is cooled to 77K by pouring liquid nitrogen in the teflon container,
the black cylindrical pellet becomes superconducting. If the magnet is placed
underneath the superconductor (with some spacer in between) when it is being
cooled, some flux gets “trapped” in the superconductor. If the flux is “pinned”,
then the magnet is forced to remain at the same position even when the
spacer is removed. Even removing the magnet and putting it back while the
superconductor is still cold forces the magnet to take the same position as
before.
