ELECTRONIC-STRUCTURE OF CUO2 PLANES - FROM INSULATOR TO SUPERCONDUCTOR

Using angle-resolved photoemission and linearly polarized synchrotron radiation, we measured the electronic band structure of electronic sta tes of CuO2 plane materials ranging from insulators (Sr2CuO2Cl2) to ov erdoped superconductors (Bi2Sr2CaCu2O8+x). We report three results: (i ) The CuO2 containing insulator possesses a spin-density-wave (SDW) gr ound state; (ii) there are precursors df the SDW state for underdoped Bi2Sr2CaCu2O8+x; (iii) an extended saddle-point-type van Hove singular ity is neither a necessary nor a sufficient condition for a high super conducting transition temperature, T-c.