Superconductivity

The first systematic studies of the dependence of electrical resistance on temperature had been undertaken by L.P. Cailletet (1832–1913), E. Bouty (1846–1922) and Z.F. Wroblewski (1845–1888) in 1885. Their researches led them to the assertion that it would not be unreasonable to expect a zero value for the resistance for a temperature higher than −273°C. The next set of exhaustive measurements of the electrical resistance of various metals were performed by James Dewar (1842– 1923) and John Ambrose Fleming (1849–1945). In 1896 they completed a study of the resistance of mercury at liquid air temperature, and their results indicated that the resistance of mercury could vanish at zero degrees Kelvin.

After having liquefied helium in 1908, Heike Kamerlingh Onnes (1853–1926), in 1911, at Leiden, measured the resistance of platinum and that of puremercury at helium temperatures. He found that at 3K the value of the resistance of pure mercury became 0.0001 times the value of the resistance of solid mercury at 0°C, extrapolated from the melting point. Later that year the phenomenon was reaffirmed at 4.19K. By 1913 it was realized that impurities did not play any role in hindering the disappearance of the ordinary resistance, and the phenomenon was for the first time called the “superconductivity” of mercury [22]. In 1914 Kamerlingh Onnes discovered that an external magnetic field could disturb superconductivity by “generating resistance” in lead and tin. It was, also, found that superconductivity was destroyed when current above a certain threshold value passed through the superconductor.