superconductivity

Increase in electrical conductivity at low temperatures. The resistance of some metals and metallic compounds decreases uniformly with decreasing temperature until at a critical temperature (the superconducting point) the resistance suddenly falls to zero. The phenomenon was discovered, at temperatures within a few degrees of absolute zero (0 K/−273.15°C/−459.67°F), by Dutch scientist Heike Kamerlingh Onnes in 1911.

Some metals, such as platinum and copper, do not become superconductive; as the temperature decreases, their resistance decreases to a certain point but then rises again. Superconductivity can be nullified by the application of a large magnetic field. In the superconducting state, an electric current will continue indefinitely once started, provided that the material remains below the superconducting point. In 1986, IBM researchers achieved superconductivity with some ceramics at −243°C/−405°F, opening up the possibility of ‘high-temperature’ superconductivity; a year later Paul Chu at the University of Houston, Texas, USA, achieved superconductivity at −179°C/−290°F, a temperature that can be sustained using liquid nitrogen. Researchers are trying to find a material that will be superconducting at room temperature; so far the highest temperature at which superconductivity has been produced is 138 K/−135°C/−211°F.

In 2001, there was a trial in Detroit, Michigan, USA, in which 30,000 homes received electricity through cables made superconductive with liquid nitrogen. 150,000 homes in Denmark also underwent a similar trial.

Increasingly, high-temperature superconductors are finding commercial applications. Bismuth-based compounds can now be made into superconducting wires and coils which are used in electric power generation applications. Thallium- and yttrium-based compounds can be formed into thin films used in the manufacture of electronic devices. Future products may include superconducting motors, generators, magnets, and power cables.