Charge modulation driven Fermi surface of Pb-Bi2201

Due to doping with lead it is well known that the about (1 x 5) superstructure of Bi cuprate superconductors will be suppressed. Nevertheless, a Fermi surface map of Bi2-yPbySr2-xLaxCuO6+δ with x=0.4 and y=0.4 determined by angular resolved photoemission (ARPES) revealed additional Fermi surface (FS) features. Here a La content of x=0.4 means optimum hole doping for a maximum value of Tc and for a Pb amount of y=0.4 one commonly expect complete suppression of the superstructure. Low energy electron diffraction of these samples showed no sign of a superstructure. Scanning tunnelling microscopy, on the other hand, revealed directly two modulations of the electron density of much weaker amplitude, one long-range modulation of about (1 x 32) periodicity and a second of about (12 x 12). By taking into account the wave vectors and intensities of these two modulations the corresponding Fermi surface has been simulated, which agrees strikingly good with the experimental one. The occurrence of modulations in these high-Tc superconductors will be further discussed. (orig.)