Heike Kamerlingh Onnes (Dutch: [ˈɦɛikə ˈkaːmərlɪŋ ˈɔnəs]; 21 September 1853 – 21 February 1926) was a Dutch experimental physicist who became the first to liquefy helium, cooling it to near 1.5 kelvin (K). For this work, he was awarded the Nobel Prize in Physics in 1913.
In 1911, using liquid helium to investigate the electrical conductivity of solid mercury, Kamerlingh Onnes found that its electrical resistance vanishes at 4.2 K, i.e. superconductivity.
The Leiden scale (°L or ÐL) is a temperature scale that was used to calibrate low-temperature indirect measurements in the early 20th century, by providing conventional values (in kelvins, then termed "degrees Kelvin") of helium vapour pressure. The scale dates back at around 1894, when Heike Kamerlingh Onnes established his cryogenics laboratory in Leiden, Netherlands. It was used below −183 °C, the starting point of the International Temperature Scale in the 1930s (Awbery 1934). The boiling points of standard hydrogen (−253 °C), consisting of 75% orthohydrogen and 25% parahydrogen, and oxygen (−183 °C) were used as fixed points, corresponding to zero and 70 on the scale respectively.
Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source.
The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes. Like ferromagnetism and atomic spectral lines, superconductivity is a phenomenon which can only be explained by quantum mechanics. It is characterized by the Meissner effect, the complete cancellation of the magnetic field in the interior of the superconductor during its 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 physics, the Bardeen–Cooper–Schrieffer (BCS) theory (named after John Bardeen, Leon Cooper, and John Robert Schrieffer) is the first microscopic theory of superconductivity since Heike Kamerlingh Onnes's 1911 discovery. The theory describes superconductivity as a microscopic effect caused by a condensation of Cooper pairs. The theory is also used in nuclear physics to describe the pairing interaction between nucleons in an atomic nucleus.
It was proposed by Bardeen, Cooper, and Schrieffer in 1957; they received the Nobel Prize in Physics for this theory in 1972.