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
Harm Kamerlingh Onnes Harm Kamerlingh Onnes Harm Henrick Kamerlingh Onnes (15 February 1893 – 20 May 1985 in Leiden) was a Dutch portrait painter and ceramist, who also produced designs for stamps and stained-glass windows. He is best known for the small, humorous vignettes of everyday life. Kamerlingh Onnes was born in Zoeterwoude in 1893. His father Menso Kamerlingh Onnes was a painter and member of the Hague School, who in 1911 gave his son permission to develop as an artist. He also gave him his first drawing and painting lessons. One of his uncles was the painter Floris Verster, and another uncle