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A superconductor is a material that achieves superconductivity, which is a state of matter that has no electrical resistance and does not allow magnetic fields to enter. An electric current in a superconductor can persist indefinitely.
Superconductivity can usually only 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 trains out of the track to reduce friction. Researchers are now trying to find and develop superconductors that operate at higher temperatures, which would revolutionize the transport and storage of energy.
Who discovered superconductivity?
The credit for the discovery of superconductivity goes to 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 discovered that the electrical resistance of mercury had completely disappeared when it dropped the temperature below 4, 2 Kelvin – that’s just 4.2 degrees Celsius (7.56 degrees Fahrenheit) above absolute zero.
To confirm this result, Onnes applied an electric current to a supercooled mercury sample, then disconnected the battery. He found that the electric current persisted in the mercury without decreasing, confirming the lack of electrical resistance and opening the door to future applications of superconductivity.
History of superconductivity
Physicists have spent decades trying to understand the nature of superconductivity and its causes. They discovered that many, but not all, elements and materials become superconducting when cooled below a certain critical temperature.
In 1933, physicists Walther Meissner and Robert Ochsenfeld discovered that superconductors “expel” any nearby magnetic fields, which means weak magnetic fields cannot penetrate far inside a superconductor, according to Hyper Physics, an educational site of the physics and astronomy department. This phenomenon is called the Meissner effect.
It wasn’t until 1950 that theoretical physicists Lev Landau and Vitaly Ginzburg published a theory of how superconductors worked, according to Ginzburg’s biography on the Nobel Prize’s website. Although successfully predicting the properties of superconductors, their theory was “macroscopic,” meaning that it focused on the large-scale behaviors of superconductors while ignoring what was happening at the microscopic level.
Finally, in 1957, physicists John Bardeen, Leon N. Cooper, and Robert Schrieffer developed a comprehensive microscopic theory of superconductivity. To create electrical resistance, electrons in a metal must be able to bounce freely. But when the electrons inside a metal get incredibly cold, they can pair up, preventing them from bouncing back. These pairs of electrons, called Cooper pairs, are very stable at low temperatures, and without “free” electrons to bounce back, the electrical resistance disappears. Bardeen, Cooper, and Schrieffer put these 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 drops below a critical temperature, the electrons in the metal form bonds called Cooper pairs. Locked in this way, electrons cannot provide any electrical resistance and electricity can pass through metal perfectly, according to the University of Cambridge.
However, it only works at low temperatures. When the metal gets too hot, the electrons have enough energy to break the bonds of the Cooper pairs and start offering resistance again. This is why Onnes, in his original experiments, found that mercury behaves like a superconductor at 4.19 K, but not at 4.2 K.
What are superconductors used 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 (NMRI), the machines use strong electromagnets, as described by the Mayo Clinic. These powerful electromagnets would melt normal metals due to the heat of even a little resistance. However, since superconductors have no electrical resistance, no heat is generated and electromagnets can generate the necessary magnetic fields.
Similar superconducting electromagnets are also used in maglev trains, experimental nuclear fusion reactors, and high-energy particle accelerator laboratories.
Essentially, whenever you need a very strong magnetic field or electric current and you don’t want your equipment to melt the moment you turn it on, you need a superconductor.
“One of the most interesting applications of superconductors is in quantum computers,” said Alexey Bezryadin, condensed matter physicist at the University of Illinois at Urbana-Champaign. Due to the unique properties of electric currents in superconductors, they can be used to build quantum computers.
“Such computers are made up of quantum bits or qubits. Qubits, unlike conventional information bits, can exist in quantum superposition states of being ‘0’ and ‘1’ at the same time. Superconducting devices can exist in quantum superposition states of being ‘0’ and ‘1’ at the same time. emulate that, ”Bezryadin told Live Science. “For example, current in a superconducting loop can flow clockwise and counterclockwise at the same time. Such a state is an example of a superconducting qubit.”
What are the latest advances in superconductor research?
The first challenge for researchers today is to “develop superconducting materials under ambient conditions, because currently superconductivity only exists at very low temperature or at very high pressure”, said Mehmet Dogan, postdoctoral researcher at the University of California at 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 are separated into two main categories: low temperature superconductors (LTS), also called conventional superconductors, and high temperature superconductors (HTS), or unconventional superconductors. LTS can be described by BCS theory to explain how electrons form Cooper pairs, while HTS uses other microscopic methods to achieve zero resistance. One of the major unresolved issues in modern physics is the origins of HTS.
Most of the historical research on superconductivity has been directed towards LTS, as 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 modern research. Anything that operates as a superconductor above 70K is generally considered an HTS. Even though 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 down to even higher temperatures. bass required by LTS.
The future of superconductors
The “holy grail” of superconductor research is to find a material that can act as a superconductor at room temperature. The highest superconducting temperature to date has been achieved with extremely pressurized carbon sulfur hydride, which achieved superconductivity at 59 F (15 C, or about 288 K), but required 267 gigapascals of pressure to do it. This pressure is equivalent inside giant planets like Jupiter, making it impractical for everyday applications.
Superconductors at room temperature would allow electrical transmission of energy without loss or waste, more efficient maglev trains, and cheaper and more ubiquitous use of MRI technology. The practical applications of room temperature superconductors are limitless – physicists just need to understand how superconductors work at room temperature and what the “Goldilock” material might be for superconductivity.
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