Fine-structure in the low-energy excitation spectrum of a high-T-c superconductor by polarization-dependent photoemission - art. no. 100504

Angle-resolved photoemission spectroscopy is performed on single crystals o f the single-layer high-T-c superconductor Bi2Sr2-xLaxCuO6+delta at optimal doping (x=0.4) in order to study in great detail the Zhang-Rice (ZR) singl et band at the Fermi level. Besides the high crystal quality the advantages of a single-layer material are the absence of bilayer effects and the dist inct reduction of thermal broadening. Due to the high energy and angle reso lution and, most important, due to the controlled variation of the polariza tion vector of the synchrotron radiation, the emission from the ZR singlet band reveals a distinct fine structure. It consists of two maxima, the firs t showing only weak and the second at E-F extremely strong polarization dep endence. However, our observation has enormous consequences for line-shape analyses and the determination of pseudogaps by photoemission.