Before Kamerlign Onnes, in 1908, was able to liquefy helium and bring its temperature down to about 1K, it had been known that the resistance of a metal falls when cooled below room temperature. However, it was not known what value the resistance would approach if the temperature was reduced towards 0K until Onnes, while experimenting with platinum, discovered that, its resistance fell when cooled to a very low value that depended on the metal’s purity.

    As the temperature of mercury was reduced toward 0K, the value of the resistance would fall smoothly until the resistance fell extremely suddenly at about 4K. Below 4K, mercury passed into a new state with electrical properties unlike those previously known: this new state that mercury had entered was called the “superconducting state.”

Title Page
Introduction to Superconductors
Basic Conditions
The Resistance in a Superconductor
The Two Types of Superconductors
Applications of Superconductors