“Introduction to the Structure and Chemistry of Superconducting Materials”, 1997-08 ():
The copper oxide superconductors are the latest and in some ways the most exotic of the series of new superconducting materials discovered during many decades of scientific research in the materials aspects of superconductivity.
This tutorial lecture, summarized in part in the following, was designed to place the cuprate superconductors, for the non-expert, within the context of the superconducting materials which came before and bring all up to date on the latest developments in cuprates, where even after a decade of intensive research, new materials are being discovered which challenge our understanding.
…It would have been useful indeed in the early days of the field to have set up a “commission” to set some minimum standard of data quality and reproducibility for reporting new superconductors. An almost countless number of “false alarms” have been reported in the past decade, some truly spectacular. Koichi Kitazawa from the University of Tokyo coined these reports “USOs”, for Unidentified Superconducting Objects, in a clever cross-cultural double entendre likening them to UFOs (Unidentified Flying Objects, which certainly are their equivalent in many ways) and to “lies” [uso] in the Japanese translation of USO. These have caused great excitement on occasion, but more often distress. It is important, however, to keep in mind what a report of superconductivity at 130K in a ceramic material two decades ago might have looked like to rational people if it came out of the blue sky with no precedent. That having been said, it is true that all the reports of superconductivity in new materials which were later confirmed to be true did conform to some minimum standard of reproducibility and data quality. I have tried to keep up with which of the reports have turned out to be true and which haven’t. There have been two common problems:
Experimental error—due, generally, to inexperienced investigators unfamiliar with measurement methods or what is required to show that a material is superconducting.
This has become more rare as the field matures.
“New” superconductors are claimed in chemical systems already known to have superconductors containing some subset of the components.
This is common even now, and can be difficult for even experienced researchers to avoid. The previously known superconductor is present in small proportions, sometimes in lower Tc form due to impurities added by the experimentalist trying to make a new compound. In a particularly nasty variation on this, sometimes extra components not intentionally added are present—such as Al from crucibles or CO2 from exposure to air some time during the processing. I wish I had a dollar for every false report of superconductivity in a niobium-containing oxide where the authors had unintentionally made niobium nitride in small proportions.