Ted Geballe and HTSC

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. The most prominent theoretical question for high-temperature superconductors is, ?Why is Tc so much higher in these materials than in conventional metallic superconductors?? My answer is that the dopants (often, but not always, oxygen vacancies or interstitials) have formed self-organized percolative networks to screen the strong ionic fields in and between tetragonal layers. This model fits very well to Geballe?s latest data with Tc = 84 K on apparently overdoped Mo-YBCO sol-gel samples, showing the effectiveness of self-organization.