Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared. For this discovery, he was awarded the Nobel Prize in Physics in 1913.

In subsequent decades, superconductivity was found in several other materials. In 1913, lead was found to be superconductive at 7 K, and in 1941 niobium nitride was found to be superconductive at 16 K.

The next important step in understanding superconductivity occurred in 1933, when Walter Meissner and Robert Ochsenfeld discovered that superconductors expelled applied magnetic

fields, a phenomenon that has come to be known as the "Meissner effect." In 1935 F. and H. London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current.

In 1950 Lev Landau and Vitalij Ginzburg  formulated what came to be called the phenomenological Ginzburg-Landau theory of superconductivity. This theory had great success in explaining the macroscopic properties of superconductors. In particular, Alexei Abrikosov showed that the theory predicts the division of superconductors into the two categories, now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau having died in 1968).

The complete, microscopic theory of superconductivity was finally proposed in 1957 by John Bardeen, Leon Cooper, and John Schrieffer. It came to be known as the BCS theory. Superconductivity was independently explained by Nikolay Bogolyubov . The BCS theory explained the superconducting current as a superfluid of "Cooper pairs"—pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. In 1959 Lev Gor'kov showed that the BCS theory becomes equivalent to the Ginzburg-Landau theory close to the critical temperature.

In 1962 the first commercial superconducting wire, a niobium-titanium alloy, was developed by researchers at Westinghouse Electric Corporation. In the same year, Brian Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator. This phenomenon, now called the "Josephson effect," is exploited by superconducting devices such as SQUIDs (superconducting quantum interference devices). Josephson was awarded the Nobel Prize for this work in 1973.

Until 1986, physicists had believed that the BCS theory forbade superconductivity at temperatures above about 30 K. But that year it was found by Paul C. W. Chu of the University of Houston that replacing the lanthanum with yttrium  raised the critical temperature to 92 K. This latter discovery was significant because liquid nitrogen could then be used as a refrigerant (the boiling point of nitrogen is 77 K). This is important commercially because liquid nitrogen can be produced cheaply on-site with no raw materials. Many other superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics  

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