Superconductivity in metallic

A determined search for superconductivity in metallic oxides was initiated in mid-summer of 1983 at the IBM, Zurich Research Laboratories in Riischliken, Switzerland. This research effort was an extension of previous work (145) on oxides, namely, Sr1.xCaxTiOs, which exhibited some unusual structural and ferro-electric transitions (see Section 2.2a). During the summer of 1983, the superconductivity research was focussed on copper-oxide compounds. Muller had projected the need for mixed Cu2+/Cu3+ valence states, Jahn-Teller interactions (associated with Cu2+ ions), and the presence of room temperature metallic conductivity to generate good superconductor candidates. These researchers then became aware of the publication by Michel, Er-Rakho, and Raveau (146) entitled ... 

Barbee III, T.W., Garcia, A. and Cohen, M.L., First-Principles Prediction of High-Temperature Superconductivity in Metallic Hydrogen. Nature 340 369 (1989). 

These last few years superconductivity in metals and alloys has mainly been explained with the help of the so-called Cooper electron pairs. At the low temperatures at which super-conductivity occurs, the metal ions do not vibrate any more. In that case the movement of an electron through the lattice is enough to deform that lattice. The metal ions in the vicinity of the electron move towards that electron and thus provide a net positive charge, causing a second electron to be attracted, (fig. 11.4.13b). In the figure b and c, the metal ions have been reduced in size because the figure is more clear then. 

The point is quite clear. One cannot expect to make any progress toward superconductivity in metallic polymers until there is a major improvement in materials quality to the point where the mean free path is much longer than the characteristic monomer repeat units. When this has been achieved, kpl > 1 and the resistivity will be truly metal-like, decreasing as the temperature decreases. The big unresolved question is how to realize the required improvements in structural order This remains as a major challenge to the field. 

The story of superconductivity in metallic polymers has not yet begun. If and when superconductivity is discovered in this class of materials, that discovery will create a new research opportunity that is both exciting and potentially important. 

C. C. Chen and C. M. Lieber, Isotope Effect and Superconductivity in Metal-doped Ceo, Science 259, 655-658 (1993). 

Chen, C-C. Lieber, C. (1991). Isotope effect and superconductivity in metal-doped Cgo- Science, 259, 655-8. 

The detailed experimental investigations have, at least for CeCu2Si2 and UBej3, spoiled the original hope of finding triplet superconductivity in metals similar to the known case of superfluid He. Apparently the lower symmetry and the lower purity of crystals play an essential role for the superconducting states found in heavy-fermion compounds. We would like to recall a few key observations which underline this conclusion ... 

Superconductivity in metals can be explained satisfactorily by BCS theory, first proposed by John Bardeen, Leon NeU Cooper, and John Roben Schrieffer in 1957. They received the Nobel Prize in Physics in 1972 for their work. BCS theory treats superconductivity using quantum mechanical effects, proposing that electrons with opposite spin can pair due to fundamental attractive forces between the electrons. At temperatures below Tc, the paired electrons resist energetic interference from other atoms and experience no resistance to flow. Superconductivity in ceramics has yet to be satisfactorily explained. 

Superconductivity in Metals and Alloys, PG. de Gennes (Addison-Wesley, Reading, MA, 1966). 

There is a generally accepted theory of superconductivity in metals.This theory is based on the notion that under certain conditions the electrons interact with the lattice of the solid in such a way that two electrons form a pair with opposite spins having a lower energy than two single uncorrelated electrons. The pair of electrons is called a Cooper pair. Unless the pair is broken up, it is not possible for one of the electrons to be scattered by a nucleus. Below a temperature called the transition temperature, there is not enough thermal energy to break up the pair, so that scattering does not occur and an electrical current can flow without observable resistance. 

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