High-Temperature Superconductivity—An Electron Transfer Phenomenon

Abstract

The increase of the critical temperature T c for superconductivity in Al 1 − x (SiO 2 ) x cermets with increasing x correlates with a decrease of the electron density n due to electron transfer, expressed by T c / T c , max = 1 − γ ⋅ n 2 (*). Behind the formula (*) and T c / T c , max = 1 − 82.6 ( P − 0.16 ) 2 , which is characteristic of hole-doped cuprat high-temperature superconductors, lies a general phenomenon, namely electron transfer, which equalizes potential differences in the material and leads to a strong reduction of n . P is the fraction of holes filled by the transferred electrons. A quantitative consideration gives T c ( x ) / T c , max = 1 − ( 1 − x 1 − x 0 ) 2 (**), where x is the doping concentration and x 0 is the concentration at which superconductivity begins. At x = x max = 1 the electron source is completely depleted and with further growth of x the hole density p starts to increase and T c decreases until superconductivity disappears completely at x = 2 − x 0 . Taking into account the formula (**), the hypothesis arose that for x > x max T c / T c , max = 1 − γ ⋅ p 2 (***), an analogue of the formula (*), and that superconductivity is possible not only by electron-Cooper pairs but also by paired holes. The mechanisms described here for HTSC suggest an analogy to the physics of semiconductors and that of nanocomposites: Electron-hole duality. The “ P = 1 / 8 ” anomaly in YBa 2 Cu 3 O 6+x is caused by the simultaneous presence of electrons and holes, a consequence of incomplete electron transfer.