The most familiar manifestation of superconductivity is zero electrical resistance, first discovered in mercury by Kammerlingh Onnes in 1908. It took 70 years to develop a satisfactory explanation in terms of "Cooper pairs" or electrons bound together by their mutual distortions of the crystal lattice (sometimes described as "two bowling balls in a waterbed") - the so-called electron-phonon interaction.

It is useful to define a few symbols used in discussing superconductivity. We may then be more precise in describing zero electrical resistance and its natural application: resistance-less wire.

However, an equally interesting property of superconductors (from the point of view of a physicist) is their perfect diamagnetism and its limitation by magnetic flux penetration. I will deal with these phenomena in some detail later.

But first I should complete this mini-survey of the properties of superconductors by listing the most mysterious of all: the phenomenon of macroscopic quantum interference as manifest in what I believe will ultimately prove the most useful of all superconducting devices: the superconducting quantum interference device or SQUID. This and its cousins offer the promise of quantum electronics using superconductors.

But we should not expect the money to start rolling in right away. Consider the example of transistors: from their invention: to their significant impact in the marketplace took nearly 30 years, and they were much easier to understand than superconductors!

Nevertheless, we are already starting to see some significant commercialization of the high-temperature superconductors discovered in 1987.

As of 1985, only a few materials were considered significant superconductors, and those were (not surprisingly) all metals. But in 1986 and 1987 everything changed with the discovery of copper oxide superconductors, which broke the liquid nitrogen barrier for the first time and made the 1900's the century of superconductivity.

Meanwhile superconductivity has been developing in parallel with µSR....

The use of µSR as a probe of the superconducting state was proposed in the early 1970's and first used on Pb(0.9)In(0.1) years before HTSC appeared on the scene. In the years just before 1986, more work was done with µSR on magnetic superconductors like ErRh4B4 which turned out to be a fortuitous ideal preparation for studies of the cuprates, all of which have a magnetic parent state! The action began for the µSR community in 1987 at TRIUMF. But I am getting ahead of myself....

Jess H. Brewer
Last modified: Wed Mar 11 16:32:43 EST 1998 ±