A hundred years of superconductivity
Heike Kamerlingh Onnes discovered superconductivity on 8 April 1911. Superconductivity can be described as electrical force with zero resistivity. Today, superconducting magnets are an integral part of top-level physical and medical research. Physicist Peter Kes is one of the organisers of a symposium commemorating a hundred years of superconductivity.
The discovery of superconductivity in 1911, in the building that now houses Leiden's School of Law, has become something of a myth in the world of physics. It is said to have been a chance discovery, the result of an apprentice instrument-maker to Kamerlingh Onnes who dropped off to sleep while operating a piece of cooling equipment.
Peter Kes has consulted Kamerlingh Onnes' own notebooks in the Boerhaave Museum: 'It was quite a job to decipher his notes. At the start he was very neat, but once he gets onto his measurements, it all becomes much messier. ' What is clear is that Kamerlingh Onnes was systematically occupied with measuring the electrical resistance of a range of different metals at the lowest possible temperatures.
'Virtually zero' he notes on 8 April 1911 in his notebook when the resistance in mercury at 3 degrees above absolute zero (3.0 kelvin) exhibits no measurable value. These were still the early days of Max Planck and Albert Einstein's quantum theory, but Leiden physicists were already using a primitive quantum model of a metal that predicted an 'unmeasurable' resistance at absolute zero. According to classical physics, the conducting electrons 'freeze', with the result that rather than decreasing, the resistance becomes infinite.
Kes: 'The conclusion was that resistance in gold should also have been 'virtually zero'. But we knew that this was not the case because of impurities in the metal. The importance of this disappearing resistance was not immediately appreciated, because nobody realised that the resistance was literally zero. And, even had Kamerlingh Onnes wanted to, he would not have been able to do anything with his discovery because mercury is difficult to manipulate; you can't simply wind it around a reel.'
|Professor Peter Kes is a busy man. On 8 April there is the symposium on ‘100 Years of Superconductivity’, that he is organising together with Professor Dirk van Delft. On the same day a BBC camera team will be in Leiden filming for a documentary about the history of electricity, a field in which Leiden has played a significant role. And in the summer there is a large international scientific conference in Chicago where Kes will be presented with the Abrikosov Prize in Vortex Physics for his contribution to research on superconductivity.|
Kamerlingh Onnes was awarded the Nobel Prize in 1913 for making helium liquid, and in his acceptance speech he mentioned superconductivity. He even foresaw superconducting magnets with a field strength of 10 tesla, which was considered fantastically high at the time. You can conduct a lot of current through a wire that has no resistance without the wire melting, and the current determines the strength of the magnetic field.
'The disappointment was enormous when this failed,' comments Kes. The first superconductors were only able to resist weak magnetic fields before again acquiring normal resistance. It was only much later that superconducting materials were discovered that are resistant to high magnetic fields, which made field strengths up to above 20 tesla possible.'
At the present time it would impossible to imagine life without superconducting magnets in large particle accelerators, top-level MRI scans and extreme cooling equipment. Leiden researchers, including Tjerk Oosterkamp and Dirk Bouwmeester, are involved in pioneering research in this field. Oosterkamp aims to scan protein molecules with a nanoscale probe to discover their structure, and Bouwmeester wants to discover the basics of quantum theory. Both researchers use extreme magnetic fields to tap heat from their laboratory specimens, so that the temperature can be brought down to millikelvins. Only then can some of nature's secrets be revealed.
Leiden research profile area Fundamentals of Science
(23 March 2011)