Superconductivity

Heat is the energy of motion of tiny particles, the vigorous dance of the atoms and molecules that constitute matter. When matter is chilled, the dance becomes torpid. At Absolute Zero ( --273.13 degrees C.) it would cease altogether. Scientists have not attained and do not expect to attain absolute Absolute Zero, but by a laborious process which involves repeated magnetization and demagnetization they have chilled certain salts to .0002 of one degree above Absolute Zero (TIME, Feb.

25, 1935).

An electric current is simply the passage of electrons through a conductor. The greater the number of electrons, the higher the amperage of the current. At normal temperatures the electrons, pushed by the voltage, make the best individual progress they can through the maze of atoms, and they are impeded by the atomic dance. If the conductor is progressively chilled, the resistance to the current should fall off as the atomic dance slows down. In theory, the resistance should diminish in a smooth curve until it vanishes entirely at Absolute Zero, where the electrons would encounter no more opposition than would an army marching through the serried ranks of an enemy frozen stockstill. In practice, the resistance does fall in a smooth curve down to one or two degrees above Absolute Zero where it vanishes abruptly although some slight heat is left in the conductor. Then an electric current started in a ring of lead will keep going around the ring indefinitely. This phenomenon is called superconductivity.

In its leading article last week, Technology Review (Massachusetts Institute of Technology) sets forth a tentative explanation of why superconductivity, the condition of no resistance, occurs before the atomic dance has entirely stopped. At ordinary temperatures the electrons are dispersed and disorganized by the vibration and must make their way alone. But, in the view of Professor John Clarke Slater, head of M. I. T.'s physics department, in the neighborhood of Absolute Zero the atomic interference is so feeble that electrons may combine in large swarms and travel along together like mountain climbers tied together by a rope. By virtue of this "co-operation," the faint show of opposition that might impede one electron impedes the swarm not at all, and electrical resistance is therefore nil.

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