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Discovered more than 100 years ago, superconductivity continues to captivate scientists who seek to develop components for highly efficient energy transmission, ultrafast electronics or quantum bits for next-generation computation. However, determining what causes substances to become—or stop being—superconductors remains a central question in finding new candidates for this special class of materials.
In potential superconductors, there may be several ways electrons can arrange themselves. Some of these reinforce the superconducting effect, while others inhibit it. In a new study, scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory have explained the ways in which two such arrangements compete with each other and ultimately affect the temperature at which a material becomes superconducting.
Superconducting - State - Electrons - Cooper - Pairs
In the superconducting state, electrons join together into so-called Cooper pairs, in which the motion of electrons is correlated; at each moment, the velocities of the electrons participating in a given pair are opposite. Ultimately, the motion of all electrons is coupled—no single electron can do its own thing—which leads to the lossless flow of electricity: superconductivity.
Generally, the more strongly the pairs couple and the larger the number of electrons that participate, the higher will be the superconducting transition temperature.
Materials - Superconductors - Elements - Compounds - Elements
The materials that are potential high-temperature superconductors are not simple elements, but are complex compounds containing many elements. It turns out that, besides superconductivity, electrons may exhibit different properties at low temperatures, including magnetism or charge density wave order. In a charge density wave, electrons form a periodic pattern of high and low concentration inside the material. Electrons that are bound in the charge density wave do not participate in superconductivity, and the two phenomena compete.
"If you remove some electrons to put into a charge density wave, the strength of your superconducting effect will diminish," said Argonne materials scientist Ulrich Welp, a corresponding author of the study.
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