At what temperature do materials become superconductors?
Until 1986, the highest temperature at which any material was known to superconduct was 23 degrees above absolute zero. Most of the over 6,000 known superconductors enter the superconducting state at temperatures well below this value. However, in 1986 a new class of superconducting materials was discovered and, in the years since, a number of superconductors with critical temperatures above 77 K (Celsius degrees above absolute zero) have been identified. The significance of this temperature is that it is the boiling point of liquid nitrogen, an inexpensive and commonplace coolant. Prior to the discovery of these “high-temperature superconductors”, superconductivity required the presence of liquid helium, a costly and difficult-to-use cryogenic liquid.
