STRUCTURAL MODIFICATIONS IN BISMUTH CUPRATES - EFFECTS ON THE ELECTRONIC-STRUCTURE AND FERMI-SURFACE

We compare the electronic structure of the idealized tetragonal model of Bi2Sr2CuO6 with that of the more realistic orthorhombic 2 × 2 cell as determined by Torardi and collaborators. The distortions, which involve atomic displacements as large as 0.45, shift the Bi-O(3) derived bands at the Fermi level strongly, and change the number of Fermi surfaces and their topology. We emphasize that such complications, which are probably even larger in Bi2Sr2CaCu2O8, must be taken into acount in the interpretation of angle-resolved photoemission spectroscopy (ARPES), since we find for this compound several Fermi surfaces in the region of the M point where flat bands are seen in ARPES data. These effects will also affect the interpretation of the measured superconducting energy gap over the Fermi surface(s). © 1995 The American Physical Society.