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Superconductivity is a phenomenon in which an electrical circuit loses its resistance and becomes extremely efficient under certain conditions. There are several ways this can happen that were thought to be incompatible. For the first time, researchers discover a bridge between two of these methods of achieving superconductivity. This new knowledge could lead to a more general understanding of phenomena and one day to applications.
If you are like most people, there are three states of matter in your daily life: solid, liquid and gas. You may be familiar with a fourth state of matter called plasma, which is like a gas that has become so hot that all of its constituent atoms have separated, leaving behind a super hot mess of subatomic particles. But did you know of a so-called fifth state of matter at the opposite end of the thermometer? It is known as Bose-Einstein condensate (BEC).
“A BEC is a unique state of matter in that it is not made up of particles, but rather waves,” said associate professor Kozo Okazaki of the Tokyo University Institute for Solid State Physics. “When they cool down to near absolute zero, the atoms of some materials are smeared into space. This smear increases until the atoms – now more wave-like than particle-like – overlap, becoming indistinguishable from each other. is a single entity with new properties that previous solid, liquid or gaseous states, such as superconducting, lacked. Until recently superconducting BECs were purely theoretical, but we have now demonstrated this in the laboratory with a new material based on iron and selenium (a non-metallic element). “
This is the first time that a BEC has been experimentally verified to function as a superconductor; however, other manifestations of matter, or regimes, can also give rise to superconduction. The Bardeen-Cooper-Shrieffer (BCS) regime is an arrangement of matter in such a way that, when it is cooled to near absolute zero, the constituent atoms slow down and align, which allows electrons to pass more easily. This effectively brings the electrical resistance of such materials to zero. Both BCS and BEC require freezing conditions and both involve slowing down of the atoms. But these regimes are otherwise quite different. For a long time, researchers believed that a more general understanding of superconduction could be achieved if these regimes overlapped in some way.
“Demonstrating the superconductivity of BECs was a means to an end; we really hoped to explore the overlap between BEC and BCS,” Okazaki said. “It has been extremely challenging, but our unique observation apparatus and method has verified it: there is a smooth transition between these regimes. And this suggests a more general theory behind superconduction. It is an exciting time to work in this field. .. “
Okazaki and his team used the ultra-low-temperature, high-resolution laser-based photoemission spectroscopy method to observe how electrons behaved during the transition of a material from BCS to BEC. The electrons behave differently in the two regimes, and the change between them helps fill some gaps in the larger picture of superconduction.
But superconduction is not just a laboratory curiosity; superconducting devices such as electromagnets are already used in applications, the Large Hadron Collider, the largest particle accelerator in the world, is one example. However, as explained above, these require ultra-cold temperatures which prohibit the development of superconducting devices that we might expect to see every day. So it’s not surprising that there is great interest in finding ways to form superconductors at higher temperatures, perhaps someday even at room temperature.
“With conclusive evidence of superconducting BECs, I think it will prompt other researchers to explore superconducting at ever higher temperatures,” Okazaki said. “It may sound like science fiction for now, but if superconduction can occur close to room temperature, our ability to produce energy would greatly increase and our energy needs would decrease.”
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