Superconductivity

Certain materials, known as superconductors (hereafter SC's), when cooled below a certain critical temperature (Tc), exhibit extraordinary properties including resistance-less electrical conductivity and reflection of magnetic fields. Unfortunately, known SC's must be cooled far below room temperature. Usually liquid nitrogen is used for the cooling. If room-temperature SC's could be created it would be a huge economic and energy boon.

In high school I made it all the way to the state science fair with a project that was, at heart, stupidly simple, but which used some uncommon materials and machinery.

For the project I asked, "How much longer can the life of a superconductor be extended by insulating it in a vacuum?" I got to play around with lots of fun equipment: a SC, a wicked powerful magnet, liquid nitrogen, and a bell jar and vacuum pump, but in essence, the vacuum pump and bell jar and a thermometer would have done the trick. All I was really testing was rate of heat transfer into a vacuum.

If I had not used an overly complicated setup, however, I would never have stumbled upon an interesting discovery. As I repeatedly cooled the SC beyond Tc (the point of superconductivity), let it warm, measured the amount of time it remained superconductive, then repeated, I found that the SC remained superconductive for shorter and shorter intervals.

However, warming the SC all the way back up to room temperature (instead of just above Tc), before cooling it again "reinvigorated" the superconductor. By reinvigorated, I mean that the SC retained its superconductivity longer when it was warmed up before cooling. Assuming that the SC warmed at the same rate each time after it was cooled, then the Tc, must have risen slightly, resulting in the prolonged superconductivity. This leads to much more interesting questions than my vacuum insulation question:

• Can a period of heating above room temperature before cooling raise the Tc? By how much?
• What is the optimal temperature to heat the SC to before cooling? How high can the Tc be raised?
• Does the rate of heating/cooling affect the Tc?
• Is the assumption that the Tc is being affected accurate or could the heat conductivity of the material be affected by heating?
• What is structurally occurring inside the material due to the heating and cooling?

If anyone has answers to any of these questions, please post them at the bottom of this page or email me.

These questions were re-raised in my mind when I read this fascinating New York Times article on the structure of glass and how much science does not understand about glass. I read: "The final structure of the glass also depends on how slowly it has been cooled." and thought immediately of superconductors. Surely there is a connection here.

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