On April 8, 1911, physicist Heike Kamerlingh Onnes of Leiden University used an intricate glass cryostat to cool mercury down to just a few degrees above absolute zero. Then he scribbled down three words that ultimately marked the discovery of an entirely new physical phenomenon.
The phrase, jotted more than halfway down the page of a messy lab notebook, didn’t really match the occasion. What Kamerlingh Onnes wrote was “Mercury practically zero”, or, according to a more literal translation, “Quick[silver] near-enough dull”. But what he saw was the first evidence of superconductivity, the ability of some substances to conduct electricity with no resistance at all.
One hundred years on, superconductivity has proven both invaluable and, at the same time, frustratingly hard to implement commercially. In Science, Adrian Cho gives a good rundown of the scientific implications of the discovery, particularly the theory that emerged some four decades later to explain how electrons pair up in superconducting materials to flow without resistance. Dubbed BCS theory for its three founders – John Bardeen, Leon Cooper, and Robert Schrieffer – the explanation has led to insights into everything from neutron star physics to the fundamental forces of nature.
But real-world applications haven’t quite met expectations. In a recent feature for IEEE Spectrum, Pradeep Haldar and Pier Abetti say Kamerlingh Onnes thought superconductivity would be valuable because it could be used to transmit electricity without losing energy to heat. But, they note, so far superconductivity’s most prominent applications have capitalized on the ability to generate strong magnetic fields, a property that’s been put to use to make MRI devices and powerful particle-steering magnets at accelerators like the Large Hadron Collider.
Superconducting electrical grids aren’t yet a reality. But they are starting to come along. The proposed Tres Amigas Superstation – a hub that would connect the United States’ three power grids – is designed to use superconducting wires to carry large amounts of energy. South Korea plans to use superconducting wire to modernize its electrical grid.
Paul Michael Grant, writing for Physics World, has a great summary of the first century of superconducting science, which includes some notable details that emphasize the inherent messiness of experimentation. Grant points out, for example, that mercury, which becomes a superconductor when its temperature falls below 4.2 Kelvin, was not the best material Kamerlingh Onnes could have studied:
Ironically, had the Leiden team simply wired up a piece of lead or solder lying around the lab – rather than using mercury – their task would have been far easier, because lead becomes superconducting at the much higher temperature of 7.2 K.
And for those who wonder what Kamerlingh Onnes’s “very hard to read” notebooks have to say about the early work, Dirk van Delft and Peter Kes of Leiden University have done a detailed study, outlined in this Physics Today article (a pdf version can be found here).