- Most chemical elements can become superconductors at sufficiently low temperatures.
- Superconductivity is the ability of certain materials to conduct electric currents with no resistance and extremely low energy losses.
- Levitating trains, highly accurate magnetoencephalograms, and smaller and lighter engines, generators and transformers are some applications of superconductivity.
In the early years of the twentieth century, the Dutch physicist H. Kamerlingh Onnes and his team of researchers began to study the properties of matter at very low temperatures, between -271° C and -259° C. In 1911 they observed that the electrical resistance of mercury tends to zero (disappears) at a temperature of 4.2K (-269o C). They had just discovered superconductivity, a contribution for which they were awarded the 1913 Nobel Prize for Physics.
|What is superconductivity? It is the ability of certain materials, in specific conditions, to conduct electric current without energy loss or resistance.|
Two More Nobel Prizes for Researchers Who Made Further Advances in the Field of Superconductivity
In 1957, J. Bardeen, L. Cooper and R. Schrieffer set forth their theory, known as the BCS theory which, for the first time, explained almost all the properties of superconductive materials. Their work was recognised with the Nobel Prize for Physics in 1972. The BCS theory postulates that in the superconducting phase there is an attractive interaction, brought about by deformations in the metal lattice, between electrons that are bound together into pairs (Cooper pairs). These pairs are able to carry current without any apparent electrical resistance.
In 1986, J. G. Bednorz and K. A. Müller, working in the IBM laboratories in Switzerland, discovered superconductivity in ceramic materials and at transition temperatures that were higher than the previous limit. This was a revolutionary finding as they were soon able to identify materials that were superconductive at temperatures higher than that of the boiling point of liquid nitrogen (-196o C), which meant that they could be cooled much more easily and economically. They were awarded the 1987 Nobel Prize for Physics for their discovery. These families of materials, which have been named “high-temperature superconductors” (HTS), are of great technological interest because of their possibilities for developing new applications of superconductivity.
The Joule Effect and Cooper Pairs
A wire through which an electric current circulates becomes hot (as demonstrated, for example, in the change of colour that occurs in the element of an electric heater or in light bulb filaments). This phenomenon, known as the “Joule Effect”, is a result of electrical resistance, which occurs because the flow of electrons must overcome resistance from the atoms of the material. However, in a superconductor, the electrons bond into pairs (Cooper pairs) that flow through the material (working in concert, and in synchrony with the atomic vibrations), carrying the current with no appreciable electrical resistance.
In other words:
- When resistance drops to zero, a current can circulate within the material without any dissipation of energy because the material has ceased to offer resistance to the current flow.
- The Cooper pairs flow through solid material without creating friction.
The Meissner Effect
Besides carrying electrical currents without resistance, superconductors can expel magnetic fields, a phenomenon known as the “Meissner Effect”.
What Applications Does Superconductivity Have in Our Lives?
Generating and carrying electrical currents with very low energy losses
- Installing superconducting cables in electric transmission networks, which can then carry the same amount of power with a lower energy cost. This benefits the environment.
- Designing much smaller and lighter engines, generators and transformers, for example superconducting motors for ships, and turbines.
Production of large magnetic fields
- Improving magnetic resonance imaging (MRI) equipment in hospitals: superconductive wires of less than 1 mm in diameter allow hundreds of amps to circulate without loss of energy, which makes them ideal for bobbins creating very intense magnetic fields (above two teslas).
A ten-minute journey inside CERN (ATLAS)
- For the large magnets used in particle accelerators, for example that of CERN (European Council for Nuclear Research).
New transport systems
Since superconductors can generate large magnetic fields, it is possible to construct circuits made up of permanent magnets whereby vehicles circulate by means of magnetic levitation (literally), gliding above them. One example of this is the Maglev (magnetic levitation) train which, owing to the elimination of friction with rails, is expected to reach speeds of up to 580 Km per hour on the route from Tokyo to Osaka. It is envisaged that the first commercial Maglev service will be in operation by 2025.
Riding the superconductive Maglev train at more than 500 KM per hour
Design of new electronic devices
These high-performance electronic devices make it possible to detect very small magnetic fields and are used in extremely accurate scientific instruments. For instance, they can detect magnetic fields induced by post-synaptic currents flowing across pyramidal neurons in the brain, and hence are now being used to obtain magnetoencephalograms.
ICMA, Instituto de Ciencia de Materiales de Aragón (Materials Science Institute of Aragon), CSIC, Consejo Superior de Investigaciones Científicas (Council for Scientific Research), University of Zaragoza)
We wish to thank Luis Alberto Angurel, head of the ICMA (Materials Science Institute of Aragon) Superconductivity Group for his help in writing this article.