POSITRON STUDIES OF METALLIC YBA2CU3O7-X

Results of 2D ACAR measurements on an untwined single crystal of YBa2Cu3Ox are reported at 300 K and 30 K. The spectra display the orthorhombic symmetry appropriate to the lattice. We compare our measurements with the corresponding band theory based predictions. While some differences are present between the theory and experiment, the band theory is found to describe the overall shapes of the spectra quite well, including some detailed features; in particular, the data show the characteristic signature of the one-dimensional chain band and the associated 'ridge' Fermi surface. A comparison of the normal state (300 K) and the superconducting state (30 K) shows that, although the overall shapes are similar, the details of spectral features possess a significant temperature dependence.