The modern world runs on electricity, and wires are what carry that electricity to every light, television, heating system, cell phone and computer on the planet. Unfortunately, on average, about 5% of the power generated at a coal or solar power plant is lost as the electricity is transmitted from the plant to its final destination. This amounts to a 6 billion US dollar loss annually in the U.S. alone. For decades, scientists have been developing materials called superconductors that transmit electricity with nearly 100% efficiency. 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 penetrate. An electric current in a superconductor can persist indefinitely. Superconductivity can only typically be achieved at very cold temperatures. This resistance-free attribute of superconductors’ contrasts dramatically with standard conductors of electricity – like copper or aluminum – which heat up when current passes through them. Electric toasters and older-style incandescent light bulbs use resistance to produce heat and light, but resistance can pose problems for electronics. Semiconductors have resistance below that of conductors, but still higher than that of superconductors. Superconductive materials repel magnetic fields, making it possible to levitate a magnet above a superconductor. Another characteristic of superconductors is that they repel magnetic fields.
The credit for the discovery of superconductivity goes to 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 in the mercury completely vanished when he dropped the temperature to 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 sample of super cooled mercury, and 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. Physicists spent decades trying to understand the nature of superconductivity and what caused it. They found that many elements and materials, but not all, 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, meaning weak magnetic fields can’t penetrate far inside a superconductor. This phenomenon is called the Meissner effect.
It’s very likely that you’ve 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 powerful electromagnet. These powerful electromagnets would melt normal metals due to the heat of even a little bit of resistance. However, because superconductors have no electrical resistance, no heat is generated, and the 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. Superconductors are also used to power railguns and coilguns, cell phone base stations, fast digital circuits and particle detectors. Essentially, any time you need a really strong magnetic field or electric current and 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 for quantum computers,” said Alexey Bezryadin, a condensed matter physicist at the University of Illinois at Urbana-Champaign. Because of the unique properties of electrical currents in superconductors, they can be used to construct quantum computers. “Such computers are composed of quantum bits or qubits. Qubits, unlike classical bits of information, can exist in quantum superposition states of being ‘0’ and ‘1’ at the same time. Superconducting devices can mimic this,” Bezryadin told Live Science. “For example, the current in a superconducting loop can flow clockwise and counterclockwise at the same time. Such a state constitutes an example of a superconducting qubit.” The first challenge for today’s researchers is “to develop materials that are superconductors at ambient conditions, because currently superconductivity only exists either at very low temperatures or at very high pressures. The next challenge is to develop a theory that explains how the novel superconductors work and predict the properties of those materials.
Superconductors are separated 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 by the BCS theory to explain how the electrons form Cooper pairs, while HTS use other microscopic methods to achieve zero resistance. The origins of HTS are one of the major unsolved problems of modern-day physics. Most of the historical research on superconductivity has been in the direction of LTS, because those superconductors are much easier to discover and study, and almost all applications of superconductivity involve LTS. HTS, in contrast, are an active and exciting area of modern-day research. Anything that works as a superconductor above 70 K is generally considered an HTS. Even though that’s still pretty cold, that temperature is desirable because it can be reached by cooling with liquid nitrogen, which is far more common and readily available than the liquid helium needed to cool to the even lower temperatures that are needed for LTS. The “holy grail” of superconductor research is to find a material that can act as a superconductor at room temperatures. To date, the highest superconducting temperature was reached with extremely pressurized carbonaceous sulfur hydride, which reached superconductivity at 59 F (15 C, or about 288 K), but required 267 Giga Pascal of pressure to do it. That pressure is equivalent to the interior of giant planets like Jupiter, which makes it impractical for everyday applications.
Room-temperature superconductors would allow for the electrical transmission of energy with no losses 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 figure out how superconductors work at room temperatures and what the “Goldilocks” material to allow for superconductivity might be. All superconductors are made of materials that are electrically neutral – that is, their atoms contain negatively charged electrons that surround a nucleus with an equal number of positively charged protons. At normal temperatures, electrons move in somewhat erratic paths. They can generally succeed in moving through a wire freely, but every once in a while they collide with the nuclei of the material. These collisions are what obstruct the flow of electrons, cause resistance and heat up the material. The nuclei of all atoms are constantly vibrating. In a superconducting material, instead of flitting around randomly, the moving electrons get passed along from atom to atom in such a way that they keep in sync with the vibrating nuclei. This coordinated movement produces no collisions and, therefore, no resistance and no heat. The colder a material gets, the more organized the movement of electrons and nuclei becomes. This is why existing superconductors only work at extremely low temperatures.
If scientists can develop a room-temperature superconducting materials like Reddmatter, wires and circuitry in electronics would be much more efficient and produce far less heat. The benefits of this would be widespread. If the wires used to transmit electricity were replaced with superconducting materials, these new lines would be able to carry up to five times as much electricity more efficiently than current cables. The speed of computers is mostly limited by how many wires can be packed into a single electric circuit on a chip. The density of wires is often limited by waste heat. If engineers could use superconducting wires, they could fit many more wires in a circuit, leading to faster and cheaper electronics. Finally, with room-temperature superconductors, magnetic levitation could be used for all sorts of applications, from trains to energy-storage devices. With recent advance providing exciting news, both researchers looking at the fundamental physics of high-temperature superconductivity as well as technologists waiting for new applications are paying attention. Researchers are now trying to find and develop superconductors that work at higher temperatures, which would revolutionize energy transport and storage.
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