The role of the apical oxygen in cuprate high-temperature superconductors
This study uses first-principles calculations to investigate how apical oxygen displacement ($\delta_{api}$) affects the superconducting order parameter ($m_{SC}$) in cuprate superconductors like Bi-2212 and Hg-1201. The research shows that $\delta_{api}$ doesn't directly change the charge-transfer gap but instead modulates the effective hole doping of the CuO2 planes, which is what ultimately drives variations in superconductivity.