Superconducting materials: the whole story

arXiv:1908.04419 (2019), J Supercond Nov Magn (2019), to be included in Ted@100 Festschrift, a special issue of JSNM in honor of Ted Geballe's 100th birthday.

Ted Geballe has contributed enormously to the knowledge of superconducting materials during an illustrious scientific career spanning seven decades, encompassing groundbreaking discoveries and studies of both so-called conventional and unconventional superconductors. On the year of his 100th birthday I would like to argue that all superconducting materials that Ted investigated, as well as those he did not, have one thing in common that is not generally recognized: hole carriers. This includes PbTe doped with Tl, for which Ted has proposed that superconductivity is driven by negative-U pairing. I will discuss why hole carriers are necessary for a material to be a superconductor, and the implications of this for the understanding of the fundamental physics of superconductivity.