The Iceman Succumbeth: High-Temperature Superconductivity
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Even before BCS theory came along, scientists began trying to create superconductivity at higher temperatures. They knew that if mercury became superconductive at 4 K, other metals or alloys might, under the right conditions, become superconductive at more reasonable temperatures. Their great hope was to create superconductivity at a temperature of 77 K. While still frigid by most standards, that temperature could be created by liquid nitrogen. And liquid nitrogen is considerably cheaper and easier to work with than liquid helium.
Over the course of the last century, scientists chipped away at the evil Iceman. They made important gains, but it was slow-going. And in the grand scheme of things, they were baby steps. Iceman remained a formidable opponent.
PHYSICS FACTOID: Liquid nitrogen is much more convenient and cheaper than liquid helium because nitrogen is all around us. In fact, although we’re used to equating air with oxygen, nitrogen makes up more than two-thirds of the stuff we breathe into our lungs. Helium, by contrast, is much harder to come by, and must be extracted from gases mined in the Great Plains and elsewhere.
It wasn’t until 1986 that a giant, Armstrongian step was taken in the field.
That year, a pair of IBM scientists published research showing they had achieved superconductivity at about 30 K. More surprising than the temperature reached, though, was the material they reached it with: a ceramic oxide.
Until then, few scientists believed that using ceramics (inorganic non-metals) for superconductivity held much promise. But when others confirmed the IBM results, those doubters changed their minds pretty fast. A mad rush ensued during which researchers across the world renewed their efforts to reach that Holy Grail: superconductivity at 77 K.
Within a year, it happened, and a new field of research was born: high-temperature superconductivity.
In the years since then, scientists have been busy. They continue to push the envelope on superconductivity: As of 2006, the record of 138 K, achieved in 1994, was still standing. (Scientists have actually achieved superconductivity at temperatures as warm as 164 K, but only under high pressure).
But breaking through the high-temperature barrier represents, for our hero, SuperConductivity, the end of a battle with Iceman, not the whole war. The next great achievement – the holier-than-thou grail, if you will – is superconductivity at room temperature, without liquid nitrogen. That is many a scientist’s dream.
Another feat scientists fantasize about is the discovery of how high-temperature superconductivity works. Experts agree that BCS theory only explains superconductivity up to 40 K. A number of researchers have proffered theories to account for superconductivity higher up the Kelvin scale, but none have succeeded in settling the matter within the scientific community.
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