Scanning the issue - Special Issue on Applications of Superconductivity

The phenomenon of zero resistance at low cryogenic temperatures was discovered in 1911 by Prof. H. K. Onnes in the Netherlands in the course of studying the low-temperature properties of metals. He tried and failed to make an electromagnet of lead wire, and it was not until 1961 that the method to make superconducting materials for successful high-field magnets was discovered. Meanwhile, in 1933, another important property of superconductors was discovered experimentally by W. Meissner and R. Ochsenfeld; they found that superconductors have the tendency to exclude magnetic field. A certain class of superconductors, called Type I, can almost completely exclude magnetic field and, therefore, have almost perfect diamagnetic properties. Guided by the zero resistance and diamagnetism, a theory was developed by F. London and H. London. Even today, the London theory is used extensively in applied superconductor electronics where magnetic fields are weak. This theory assumed a function representing the superconducting electron fluid that can be thought of as a single giant quantum mechanical wave function that extends throughout the superconductor. It also revealed that magnetic flux is quantized inside superconducting loops. It was later shown that the quantum of magnetic field has the value , where is the electron charge and is Planck’s constant. In 1950, G. L. Ginzburg and L. Landau published a theory that was also phenomenologically based but, unlike the London theory, is useful for situations with strong magnetic fields, such as in the large-scale applications. The concept of electron pairing was introduced in 1956 by L. N. Cooper. The electrons are paired in “momentum space,” and are known as Cooper pairs. In 1957, J. Bardeen,