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A superconductor is a material that, when cooled below a temperature called the critical temperature, suddenly loses all its electrical resistance, allowing it to conduct electricity without loss of energy . These materials also exhibit a very peculiar magnetic property: they are perfectly diamagnetic substances, that is, they exclude magnetic field lines. This means that when placed near a magnet, the magnetic field lines pass through the sides, but do not penetrate the material.
When an electric current is induced in a superconducting material, such as a circular wire, this current continues to flow indefinitely as long as the material remains cold. This current without resistance is called supercurrent and is used, among other things, to generate very strong magnetic fields.
Superconductivity, that is, the property of a material to become a superconductor below the critical temperature, was discovered in 1911 and completely stunned the physicists of the time. It took more than two decades before its diamagnetic properties (called the Meissner effect ) were discovered, and almost half a century before physicists could explain why superconductivity occurs. It was in 1957 when John Bardeen, Leon Cooper and Bob Schrieffer solved the problem, which earned them the Nobel Prize in Physics in 1972.
Critical temperature and high-temperature superconductors
The first superconductor to be discovered has a critical temperature of just 3.6 K, which is equivalent to -269.6 °C. Generating and maintaining such low temperatures is extremely difficult, which has limited the use of superconductors to a handful of very specific applications, as we’ll see later in this article.
For this reason, there are hundreds of scientists around the world who are constantly working on the development of superconductors with a critical temperature close to room temperature. These materials are called high-temperature superconductors.
Early progress raised the critical temperature by a few tens of degrees, but recently a superconductor with a critical temperature of 14.5 °C has been developed for the first time.
types of superconductors
There are basically two types of superconductors, depending on their composition and the way they interact with magnetic fields.
Type I superconductors
These were the first to be discovered. These are pure elements that exhibit the Meissner effect, that is, they repel magnetic fields when they are below the critical temperature. In general, they have a single critical temperature that is characteristic of each material, and the drop in electrical resistance below the critical temperature is abrupt.
Type II superconductors
These consist of mixtures of different elements that combine to form alloys or ceramic materials that exhibit superconductivity. What makes them different from type I superconductors is that the electrical resistance drop is gradual, so they have two critical temperatures: one when the resistance begins to drop and another when it reaches zero.
Another important feature of this type of superconductor is that if a strong enough external magnetic field is applied, the material loses its superconductivity.
Uses of superconductors
particle accelerators
Perhaps the most impressive application of superconductors to date is in the field of scientific research around particle physics. Superconductors are used in the electromagnets that keep the particle beam confined in the Large Hadron Collider, one of the largest machines built by man.
thermonuclear power
Nuclear fusion has been the dream source of clean energy for 100 years. However, to get nuclear fusion to happen and to sustain it, gaseous hydrogen and helium needs to be heated up to 100 million degrees Celsius as it spins inside a hollow donut called a Tokamak, where it is confined by powerful electromagnets made of superconductors. .
quantum computing
One of the most promising implementations of quantum computing uses superconducting circuits, which are essential for its operation.
Medical diagnostic imaging
The development of superconductors has enabled the creation of medical imaging diagnostic devices and techniques that were not possible before. One of these techniques is SQUID magnetoencephalography, which is capable of detecting changes in magnetic fields of one billionth of the magnetic field needed to move a compass needle.
electricity generation
Finally, another recent application is the use of electricity generators made of superconducting wire instead of copper wire. These generators are much more efficient than conventional ones, and much smaller and lighter.
References
Charles Slichter (2007). Introduction to the History of Superconductivity (for physics students and scientists). Retrieved from https://history.aip.org/exhibits/mod/superconductivity/01.html
Castelvecchi, D. (October 2020). First room-temperature superconductor excites—and baffles—scientists. Nature 586, 349. Retrieved from https://www.nature.com/articles/d41586-020-02895-0
Snider, E., Dasenbrock-Gammon, N., McBride, R. et al. (2020). Room-temperature superconductivity in a carbonaceous sulfur hydride. Nature 586, 373–377. Retrieved from https://www.nature.com/articles/s41586-020-2801-z#citeas
