The Winner: Superconductors
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After Heike Kamerlingh Onnes succeeded in extending the range of experiments to much lower temperatures by the liquefaction of the noble gas helium, in 1911 he discovered superconductivity, where electric current flows without detectable resistance. Superconductivity requires that distinct critical values of the temperature and magnetic field are not exceeded. Eventually it was found that a magnetic field is expelled from the interior of a superconductor, referred to as Meissner effect and representing a fundamental property of superconductors. In the mixed state, a type-II superconductor is intersected by the Abrikosov lattice of magnetic flux quanta. Magnetic flux quantization and the Josephson effect are discussed. The first microscopic theory, the BCS theory, explains superconductivity in terms of a macroscopic quantum state formed by pairs of electrons (Cooper pairs) attracted to each other because of their interaction with phonons. The motion of the magnetic flux quanta, caused by the Lorentz force, represents the mechanism limiting the current flowing without resistance.