Superconductivity and lattice instabilities

During the past five years four distinct advances in the science of superconductivity have been made (1) Many new superconductors were discovered. Really high critical temperatures have for the first time been discovered in non-cubic materials. (2) Overwhelming evidence for a connection between moderate-to-high-temperature superconductivity and low temperature structural instability was found. Work on both the occurrence and the pressure dependence of superconductivity and lattice instability in zirconium-vanadium, hafnium-vanadium, lanthanum-ruthenium, ruthenium-vanadium, copper-molybdenum-sulfide, copper-molybdenum-selenide, zinc-molybdenum-sulfide, gold-zinc, lanthanum-sulfide, and lanthanum-selenide shows that the connection between the two phenomena is very general. (3) An empirical correlation between the shape of electrical resistivity versus temperature curve of a given superconductor and its transition temperature was developed despite incomplete understanding of its nature, this correlation was found to be useful in predicting superconductivity in some cases. (4) The transition temperatures of magnesium and gold 5 x 10-4 and 2 x 10-4 k, respectively were found by means of extrapolation.