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
Wander Johannes de Haas de Haas started paralegal studies in 1895. After completion of two of three parts of the examinations and having worked in a lawyer's office for some time, he decided to change career and become a physicist instead. After passing the qualifications exams for admission to University, he started to study physics at the University of Leiden in 1900 under Heike Kamerlingh Onnes and Johannes Petrus Kuenen. He earned his doctorate in 1912, under Kamerlingh Onnes, with a thesis entitled: "Measurements on the Compressibility of Hydrogen." After getting his degree, de Haas worked in Berlin as a researcher at the Physikalische