Fermi Surface Map of the Single-Layer Bi-Cuprate Bi2Sr2 − xLaxCuO6 + δ at Optimal Doping

Abstract

A first Fermi surface map of a single-layer high-Tc superconductor is presented. The experiments were carried out on optimally doped Bi2Sr2 − xLaxCuO6 + δ (x = 0.40) with synchrotron radiation which allow to discuss in detail the strong polarization dependence of the emissions near the Fermi edge. For the cuprates, only little is known about the impact of the electron–photon matrix element determining the photoelectron intensity. For the example of the model layered superconductor Bi2Sr2 − xLaxCuO6 + δ, it will be demonstrated that the polarization geometry has significant influence on the energy distribution curves at EF, and consequently also for the determination of the topology and character of the Fermi surface (FS) by angle-resolved photoemission. For further clarification also, a FS map of the n = 2 material Bi-2212 has been measured applying a different polarization geometry as previously used by Saini et al. In the context of the current debate on the character of the FS of Bi-cuprates, our results confirm a hole-like FS for n = 1 as well as for n = 2 material, what might be the universal FS for high-Tc superconductors.