A superconductor is a material that achieves superconductivity, which is a state of matter that has no electrical resistance and does not allow the penetration of magnetic fields. An electric current in a superconductor can persist indefinitely.
Superconductivity can only normally be achieved at very cold temperatures. Superconductors have a wide variety of everyday applications, from MRI machines to super fast maglev trains that use magnets to levitate off-track trains to reduce friction. Now researchers are trying to find and develop superconductors that operate at higher temperatures, which would revolutionize energy transportation and storage.
Who Discovered Superconductivity?
The credit for the discovery of superconductivity lies with the Dutch physicist Heike Kamerlingh Onnes. In 1911, Onnes was studying the electrical properties of mercury in his laboratory at Leiden University in the Netherlands, when he found that the electrical resistance of mercury disappeared completely when the temperature dropped below 4.2 Kelvin, ie , only 4.2 degrees Celsius (7.56 degrees) Fahrenheit) above absolute zero.
To confirm this result, Onnes applied an electric current to a cooled mercury sample and then disconnected the battery. He found that the electric current persisted in the mercury without diminishing, confirming the lack of electrical resistance and opening the door to future superconductivity applications.
History of superconductivity
Physicists spent decades trying to understand the nature of superconductivity and what caused it. They found that many, but not all, elements and materials become superconductors when cooled below a certain critical temperature.
In 1933, physicists Walther Meissner and Robert Ochsenfeld discovered that superconductors “expel” any nearby magnetic field, meaning that weak magnetic fields cannot penetrate much into a superconductor, according to Hyper Physics, an educational site in the department. of Georgia State University of Physics and Astronomy. This phenomenon is called the Meissner effect.
It was not until 1950 that theoretical physicists Lev Landau and Vitaly Ginzburg published a theory on the operation of superconductors, according to Ginzburg’s biography on the Nobel Prize website. Despite being successful in predicting the properties of superconductors, his theory was “macroscopic,” that is, he focused on the large-scale behaviors of superconductors while still knowing what was happening at the microscopic level.
Finally, in 1957, physicists John Bardeen, Leon N. Cooper, and Robert Schrieffer developed a complete microscopic theory of superconductivity. To create electrical resistance, the electrons in a metal must be free to bounce. But when electrons inside a metal become incredibly cold, they can mate and prevent them from bouncing. These pairs of electrons, called Cooper pairs, are very stable at low temperatures and, without “bouncing” electrons bouncing, the electrical resistance disappears. Bardeen, Cooper, and Schrieffer put these pieces together to form their theory, known as the BCS theory, which they published in the journal Physical Review Letters.
How do superconductors work?
When a metal falls below the critical temperature, the electrons in the metal form bonds called Cooper pairs. Blocked in this way, electrons cannot provide any electrical resistance and electricity can flow perfectly through the metal, according to the University of Cambridge.
However, this only works at low temperatures. When the metal heats up too much, the electrons have enough energy to break the bonds of the Cooper pairs and again offer resistance. Therefore, Onnes, in his original experiments, found that mercury behaved like a superconductor at 4.19 K, but not at 4.2 K.
What are superconductors for?
It is very likely that you have encountered a superconductor without realizing it. In order to generate the strong magnetic fields used in magnetic resonance imaging (MRI) and nuclear magnetic resonance imaging (NMR), the machines use powerful electromagnets, as described in the Mayo Clinic. These powerful electromagnets melt normal metals due to the heat of even a little resistance. However, because superconductors have no electrical resistance, no heat is generated and electromagnets can generate the necessary magnetic fields.
Superconducting electromagnets are also used in maglev trains, experimental nuclear fusion reactors and high-energy particle accelerator laboratories, which are also used to power rail guns and coils, mobile phone base stations, fast digital circuits and particle detectors.
Essentially, every time you need a very strong magnetic field or electric current and you don’t want your computer to melt the moment you turn it on, you need a superconductor.
“One of the most interesting applications of superconductors is for quantum computers,” said Alexey Bezryadin, a physicist of condensed matter at the University of Illinois at Urbana-Champaign. Due to the unique properties of superconducting electric currents, they can be used to build quantum computers.
“These computers are made up of quantum bits or qubits. Qubits, unlike classical information bits, can exist in quantum overlay states of being” 0 “and” 1 “at the same time. Superconducting devices can mimic this.” Bezryadin told Live Science. “For example, current in a superconducting loop can flow clockwise and counterclockwise at the same time. This state is an example of a superconducting qubit.”
What’s the latest in superconductor research?
The first challenge for current researchers is to “develop materials that are superconducting under environmental conditions, because currently superconductivity only exists at very low temperatures or at very high pressures,” said Mehmet Dogan, a postdoctoral researcher at the University of California, Berkeley. The next challenge is to develop a theory that explains how new superconductors work and predict the properties of these materials, Dogan told Live Science in an email.
Superconductors fall into two main categories: low temperature superconductors (LTS), also known as conventional superconductors, and high temperature superconductors (HTS) or unconventional superconductors. LTS can be described using BCS theory to explain how electrons form Cooper pairs, while HTS uses other microscopic methods to achieve zero resistance. The origins of HTS are one of the major unsolved problems in modern physics.
Most of the historical research on superconductivity has been in the direction of LTS, because these superconductors are much easier to discover and study, and almost all applications of superconductivity involve LTS.
HTS, on the other hand, is an active and exciting area of current research. Anything that works as a superconductor above 70 K is generally considered HTS. Although it is still quite cold, this temperature is desirable, as it can be achieved by cooling with liquid nitrogen, which is much more common and readily available than the liquid helium needed to cool to even lower temperatures than they need for LTS.
The future of superconductors
The “holy grail” of superconducting research is to find a material that can act as a superconductor at room temperature. So far, the highest superconducting temperature was reached with an extremely pressurized carbon dioxide hydride, which reached superconductivity at 15 ° C (288 K), but needed 267 gigapascals of pressure to do so. This pressure is equivalent to the interior of giant planets like Jupiter, which makes it impractical for everyday applications.
Superconductors at room temperature would allow the electrical transmission of energy without loss or waste, more efficient maglev trains and a more economical and ubiquitous use of magnetic resonance technology. The practical applications of superconductors at room temperature are limitless: physicists only need to find out how superconductors work at room temperature and what the “Goldilocks” material can be to allow superconductivity.