FERMI-SURFACE TOPOLOGY OF YBA2CU3OX WITH VARIED OXYGEN STOICHIOMETRY - A PHOTOEMISSION-STUDY

High-resolution angle-resolved photoemission measurements are reported for YBa2Cu3Ox when oxygen stoichiometry x was varied between 6.3 and 6.9. Fermi surfaces were measured and their dependence on oxygen stoichiometry was monitored by observing the dispersing behavior of spectral features, scanning the entire first Brillouin zone. For x = 6.9, measured Fermi surfaces correspond very well with the plane-related Fermi surfaces calculated from band theory. Relatively small changes in Fermi surfaces were observed when oxygen stoiochiometry was varied in the range 6.5 less-than-or-equal-to x less-than-or-equal-to 6.9, where the material is metallic. However, significant changes in the spectral behavior were observed when the material becomes insulating.