HOLE LOCALIZATION IN HIGH-TEMPERATURE SUPERCONDUCTORS

Although it is generally assumed that the holes associated with oxygen-doping of high-temperature superconductors (i) are free, (ii) leave the ''charge-reservoir'' region of the dopant oxygen, and (iii) migrate to cuprate planes where they produce superconductivity and increase the;critical temperature, we find evidence of hole localization (of different types) in Tl2Ba2Can-1CunO2n+4+delta and HgBa2Can-1CunO2n+2+delta We also find that electrons, not holes, transfer to the cuprate planes as pressure or chemical pressure is applied to HgBa2Can-1CunO2n+2+delta, which also causes the critical temperature to increase.