OBSERVATION OF A SADDLE-POINT SINGULARITY IN BI-2(SR0.97PR0.03)(2)CUO6+DELTA AND ITS IMPLICATIONS FOR NORMAL AND SUPERCONDUCTING STATE PROPERTIES

We have mapped the Fermi surface (FS) of single-crystal Bi(Sr0.97Pr0.03)2CuO6+δ using angle-resolved photoemission. We find an extended saddle point at M̄ which is located very close to or at the Fermi level. This agrees with earlier photoemission data from the cuprates which reveals a striking correspondence between the position of the Fermi level relative to the saddle-point singularity and their normal state properties; however, it does not support the existence of a simple link to a high Tc. We also find that the FS is very strongly nested along the [110] direction. © 1994 The American Physical Society.