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The & # 39; electron pairing & # 39; is well above the critical temperature of the superconductor



  A characteristic of superconductivity, which goes beyond the actual superconductivity.
Panice Zhou, a graduate of Rice University, performed and analyzed "shot noise" experiments in which electron pairs were detected in lanthanum-strontium-copper oxide at temperatures above the critical temperature at which the material becomes a superconductor. Zhou measured the current flowing through nanoscale "tunnel junctions" between superconductor layers and showed that the passage of individual electrons could not explain the amount of charge flowing through the junctions. Picture credits: Jeff Fitlow / Rice University

Physicists found "electron pairing", a hallmark of superconductivity, at temperatures and energies far above the critical threshold at which superconductivity occurs.

Doug Natelson of Rice University, co-correspondent of an article on work in the nature of this week said the discovery of Cooper electron pairs "something above the critical temperature will not be crazy for some people surprising Stranger thing is that there are two different scales of energy: there is a higher energy scale on which the pairs form, and a lower energy scale, where everyone decides to band together and act together, coherently behaves that actually leads to superconductivity. "

Electrical resistance is so common in the modern world that most of us assume that computers, smartphones and electrical appliances heat up during use. This heating happens because the current does not flow freely through the metal wires and silicon chips in the devices. Instead, flowing electrons sometimes hit atoms or each other, and every collision generates a little bit of heat.

Physicists have known since 1911 that in materials called superconductors, electricity can flow without resistance. And in 1957 they found out why: Under certain conditions, including typically very cold temperatures, electrons combine in pairs – which is usually forbidden because of their mutual repulsion – and as pairs they can flow freely.

"Superconductivity, the general feeling is that you need couples and that you need to achieve some sort of coherence between them," said Natelson, who had collaborated on research with experts from Rice, the Brookhaven National Laboratory and the University of Connecticut , "The question was a long time:" When do you get couples? "Because in conventional superconductors, once you have formed pairs, coherence and superconductivity would follow."

Electron pairs are named after Leon Cooper, the physicist who first described it. In addition to the explanation of classical superconductivity, physicists believe that Cooper pairs cause high-temperature superconductivity, an unconventional variant discovered in the 1980s. It has been termed "high temperature" because it occurs at temperatures that are still very cold but significantly higher than those of classic superconductors. Physicists have long dreamed of producing high-temperature superconductors that work at room temperature. This evolution would radically change the way energy is generated, moved and used worldwide.

<div data-thumb = "https: //scx1.b -cdn.net/csz/news/tmb/2019/ahallmarkofs.jpg" data-src = "https://scx2.b-cdn.net /gfx/news/hires/2019/ahallmarkofs.jpg "data-sub- The physicists at Rice University (from left) Liyang Chen, Panpan Zhou, and Doug Natelson, as well as colleagues from the Brookhaven National Laboratory and the University of Connecticut, found evidence of electron pairing – a characteristic of superconductivity – at temperatures and energies well above the critical threshold at which superconductivity occurs. The research will be published this week in Nature . Credit: Jeff Fitlow / Rice University ">

<img src = "https://scx1.b-cdn.net/csz/news/800/2019/ahallmarkofs.jpg" alt = "A hallmark of superconductivity, beyond superconductivity itself" title = "Physicist of Rice University ( from left)) Liyang Chen, Panpan Zhou and Doug Natelson and colleagues from the Brookhaven National Laboratory and the University of Connecticut found evidence of electron pairing – a hallmark of superconductivity – at temperatures and energies well above the critical threshold at which the Superconductivity occurs this week in Nature . Photo credits: Jeff Fitlow / Rice University "/>
The physicists at Rice University (left) Liyang Chen, Panpan Zhou, and Doug Natelson, as well as colleagues from the Brookhaven National Laboratory and the University of Connecticut, found evidence of electron pairing – a hallmark of superconductivity – at temperatures and energies far beyond the critical threshold lie superconductivity occurs. The research will be published this week in Nature . Picture credits: Jeff Fitlow / Rice University

While physicists know exactly how and why electron pairings occur in classical superconductors, this does not apply to high-temperature superconductors such as the lanthanum-strontium-copper oxide (LSCO) presented in the new study.

Every The superconductor has a critical temperature at which the electrical resistance disappears. Natelson said that theories and studies on copper oxide superconductors over the past 20 years have suggested that Cooper pairs form above this critical temperature and only become coherently mobile when the material is cooled to critical temperature.

"If that's true, and you already have couples at higher temperatures, the question is," Can you get coherence even at these temperatures? "Natelson said," Can you somehow persuade her to dance in the region? known as Pseudogap, a phase space with higher temperatures and energy scales than the superconducting phase. "

In the study Nature Natelson and colleagues found evidence for this higher energy pairing in the conduction noise of high-purity LCSO2. Samples bred in the laboratory of Ivan Božović, co-author of the study in Brookhaven.

"He breeds the best material in the world and our measurements and conclusions were only possible because of the purity of these samples," Natelson said and his team have made devices called tunnel junctions, and instead of just looking at the electric current, we've looked at fluctuations in the current which are called shot noise.

"In most cases, when measuring the flow you measure a" It's something like the difference between measuring the average daily rainfall at your home and measuring the number of raindrops that fall at a given time. " By measuring the variation in the discrete amount of electrical charge flowing through LCSO transitions, Natelson and colleagues found that the passage of single electrons can not explain the amount of charge that flows through the transitions at temperatures and voltages well above Superconductivity has occurred.

"Part of the charge must be in larger pieces, the pairs," he said. "This is unusual, because in a conventional supercond, if you have the characteristic energy scale associated with superconductivity are exceeded, the pairs are torn apart and there are only individual charges ang ezeigt.

"It looks like LCSO has a different energy scale in which the couples form, but are not yet working together," said Natelson. "So far, people have been theorizing about such things, but this is the first direct proof."

 Measurement of the charge of electrons in a high-temperature superconductor
Schematic representation of the three-layer structure: superconducting lanthanum-strontium-copper oxide (LSCO) above and below and insulating lanthanum-copper oxide (LCO) in between. Credit: Brookhaven National Laboratory

Natelson said it was too early to say whether physicists could use the new insights to make couples flow unhindered at higher temperatures in unconventional superconductors. However, according to Božović, the discovery has "profound effects" on theoretical physicists studying high temperature superconductors and other types of condensed matter.

"In a sense, textbook chapters need to be rewritten," said Božović. "This study indicates that we have a new type of metal that carries a significant portion of the electrical current from electron pairs, and on the experimental side, I expect that finding will cause a lot of rework – for example, using the same technique to test other cuprates or superconductors, insulators and layer thicknesses.


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Further information:
Electron pairing in the pseudogap state by shot noise in copper oxide transitions, Nature DOI: 10.1038 / s41586-019-1486-7 ,, https://nature.com/articles/s41586-019-1486-7

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Rice University




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"Electron pairing" well above the critical temperature of the superconductor (2019, 21 August)
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