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
Kamerlingh Onnes (crater) Kamerlingh Onnes (crater) Kamerlingh Onnes is a lunar impact crater on the far side of the Moon. It lies less than a crater diameter to the north-northwest of the crater Kolhörster. North of Kamerlingh Onnes lies Shternberg and to the northwest is Weyl. This is a worn and eroded crater formation that is slightly elongated along the east–west direction, giving it a somewhat oval shape. A number of small craters lie along the rim, particularly along the northern side. The interior floor is marked only by a few small craterlets, and some ray material from the crater Ohm to the