Coupling to a phononic mode in Bi2−xPbxSr2CaCu2O8+δBi_{2-x}Pb_xSr_2CaCu_2O_{8+\delta}: Angle-resolved photoemission

The kink in the dispersion and the drop in the width observed by angle-resolved photoemission in the nodal direction of the Brillouin zone of $\mathrm{Bi_{2-x}Pb_xSr_2CaCu_2O_{8+ \delta}}$ (abbreviated as (Pb)Bi2212) has attracted broad interest [1-3]. Surprisingly optimally lead-doped (Pb)Bi2212 with $\mathrm{T_C>89K}$ as well as the shadow band were not investigated so far, although the origin of the kink and the drop is still under strong debate. In this context a resonant magnetic-mode scenario and an electron-phonon coupling scenario are discussed controversially. Here we analyze the relevant differences between both scenarios and conclude that the kink and the drop are caused by a coupling of the electronic system to a phononic mode at least in the nodal direction. It is found that besides the dispersion and the drop in the width also the peak height as a new criterion can be used to define the energy scale of the interaction, giving a new means for a precise and consistent determination of the kink energy

Systematic X-ray absorption study of hole doping in BSCCO - phases

X-ray absorption spectroscopy (XAS) on the O 1s threshold was applied to Bi-based, single crystalline high temperature superconductors (HTc's), whose hole densities in the CuO2 planes was varied by different methods. XAS gives the intensity of the so-called pre-peak of the O 1s line due to the unoccupied part of the Zhang-Rice (ZR) singlet state. The effects of variation of the number n of CuO2 - planes per unit cell (n = 1,2,3) and the effect of La-substitution for Sr for the n = 1 and n = 2 phase were studied systematically. Furthermore the symmetry of the states could be probed by the polarization of the impinging radiation.Comment: 4 pages, 2 figures, to appear in the proceedings of SCES2001, Ann Arbor, August 6-10, 200

Novel Fine-Structure in the Low-Energy Excitation Spectrum of a High-Tc Superconductor by Polarization Dependent Photoemission

Angle-resolved photoemission spectroscopy is performed on single crystals of the single-layer high-Tc superconductor Bi(2)Sr(2-x)La(x)CuO(6+d) at optimal doping (x=0.4) in order to study in great detail the Zhang-Rice (ZR) singlet 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 distinct reduction of thermal broadening. Due to the high energy and angle resolution and, most important, due to the controlled variation of the polarization vector of the synchrotron radiation the emission from the ZR singlet band reveals a distinct fine-structure. It consists of two maxima, the first showing only weak and the second at EF extremely strong polarization dependence. However, our observation has enormous consequences for line shape analyses and the determination of pseudo gaps by photoemission.Comment: 10 pages, 2 figures. to appear in PRB (Rapid Comm.