FERMI-SURFACE IN YBA2CU3O6.9 - EVIDENCE FROM ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY AND POSITRON 2-DIMENSIONAL ANGULAR-CORRELATION OF ANNIHILATION RADIATION

We assess the evidence regarding the geometry of the Fermi surface in YBa2Cu3O6.9 obtained from angle-resolved photoemission and positron two-dimensional angular correlation of annihilation radiation experiments. A detailed picture of the Fermi-surface topology of this system appears to be emerging, based on a comparison of the above-mentioned experiments with each other and with local-density-approximation calculations, although whether the Fermi surface is a manifestation of true Fermi-liquid behavior is in dispute. Some implications of these results are discussed.