Electronic structure of Bi4Sr4Ca2-xYxCu4O16 (x=0 and 1)

Electronic-structure calculations of Bi4Sr4Ca2-xYxCu4O16 for the superconducting phase (x=0) and the nonsuperconducting phase (x=1) with use of the linearized muffin-tin orbital method with the atomic-sphere approximation are reported. No dramatic difference in their electronic structures is found except that the number of holes per CuO2 unit (an important parameter in theories for high-Tc superconductivity) is about 0.27(-e) smaller in the nonsuperconducting phase. The application of directional stress along the c direction for constant unit-cell volume does not cause the number of holes in the Cu-O planes to change but the density of states at the Fermi energy does. Since Tc is strongly related to the value of the density of states at the Fermi energy in conventional superconductors, this implies that the corresponding experiment would be helpful for understanding the mechanism responsible for superconductivity. © 1992 The American Physical Society.