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discovered 02_2012

discovered 02.12 FOCUS WWW.Hzdr.DE How is superconductivity destroyed? “Superconductor“ is the term physicists use to refer to substances that do not show any electrical resistance. In the everyday life of an electrical engineer, however, the superconductivity of an electric current without energy dissipation has two flaws: it normally only works at very low temperatures and reacts very sensitively to strong magnetic fields. Therefore, although superconductivity was first observed back in 1911, it is only applied today in very special cases. To overcome these obstacles one must understand the processes at work. “We are therefore examining how superconductivity takes place and how it is destroyed“, says Joachim Wosnitza about the experiments that are being conducted at the HZDR’s High Magnetic Field Laboratory. Theoreticians explain this superconductivity without dissipation using what are known as “Cooper pairs“, which consist of two electrons. Electrons are negatively charged elementary particles that are not only fundamental components of all matter, but also conductors of electric current. In addition, electrons like many other elementary particles also possess a property physicists refer to as “spin“. In the case of electrons this spin can be either up or down. The dance of the electrons If two electrons with an opposite spin are paired, they become a Cooper pair, whereby the net spin then becomes zero and considerable changes take place regarding the pair’s quantum mechanics. Joachim Wosnitza uses an analogy to illustrate this phenomenon: “the Cooper pairs formed in a superconductor join together and as if they were dancers start to move in unison.“ Whereas with normal metals the slightest influence would divert an electron and thus disturb the conductivity of the electric current, the Cooper pairs moving in unison only lose their rhythm with a substantially higher expenditure of energy. Due to the fact that this hardly ever happens at low temperatures, such superconductors are able to conduct the electric current without resistance and thus without energy dissipation. HIGH MAGNETIC FIELD LAB: High magnetic fields like those available at the HZDR have hinted at the existence of the Fulde effect, which was originally proposed back in 1964.