The resistance to electronic conduction in a metal is caused by the scattering of the conducting electrons by phonons as well as by impurities and lattice imperfections. The diamagnetism as well as the absence of resistance of a superconductor below the critical temperature Tc leads to a model of pairs of conducting itinerant electrons of opposite spin captured in a potential well created by cooperative, dynamic atomic displacements. The Bardeen-Cooper-Schrieffer (BCS) model of superconductivity describes opposite-spin Cooper pairs of itinerant electrons captured rather than scattered below Tc by vibrating, cooperative atomic displacements. The concept of capture of pairs of itinerant or molecular orbital electrons by cooperative atomic displacements led Alex Mueller to explore with Bednorz whether dynamic, cooperative Jahn-Teller deformations might capture mobile electron pairs below a higher Tc than predicted by the BCS model. Static cooperative Jahn-Teller distortions of crystals containing Mn(III) or Cu(II) in octahedral sites had been identified as well as the role of dynamic cooperative Jahn-Teller deformations in the creation of chemical inhomogeneities in the ferrimagnetic oxospinels of the first RAM memory of the digital computer. Since superconductive electron pairs would need to be trapped itinerant electrons, a ceramic containing mixed-valent Cu(III)/Cu(II) cations was a logical choice for Alex Mueller to begin his investigation. The discovery of Bednorz and Mueller of high-temperature superconductivity in a copper oxide in 1986 broke the mindset that the BCS mechanism for capturing superconductive electron pairs was the only mechanism for the superconductive phenomenon.
Goodenough, J. B. (2017). Personal reflections on high-Tc superconductivity. In Springer Series in Materials Science (Vol. 255, pp. 73–75). Springer Verlag. https://doi.org/10.1007/978-3-319-52675-1_7