Electric current certain materials when cooled below a characteristic critical temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of "perfect conductivity" in classical physics. In a semiconductor it is sometimes useful to think of the current as due to the flow
Heike John Heike John Heike John (now Heike Walpot; born 19 June 1960) is a retired German swimmer and former astronaut candidate. She won a bronze medal at the 1977 European Aquatics Championships. She competed at the 1976 Summer Olympics in the 100 m and 200 m backstroke events but did not reach the finals. During her career she won five national titles in the 100 m (1977) and 200 m (1977, 1978) backstroke and 200 m medley (1977, 1978). She missed the 1980 Summer Olympics because of their boycott by West Germany. After her swimming career, she studied medicine at RWTH