POSITRON-ANNIHILATION IN HIGH CRITICAL-TEMPERATURE SUPERCONDUCTORS

Two dimensional angular correlation of electron-positron annihilation radiation (2D ACAR) experiments are discussed in terms of calculated positron wavefunctions and ACAR spectra for high critical temperature superconductors. It is emphasized that positron wavefunction effects are larger in these materials than, for example, the previous class of A15 superconductors. Calculations indicate that the chain derived ridge section and the S centered hole pocket may be observable in YBa2Cu3O7, in agreement with recent experiments. The plane derived Fermi surfaces are expected to be extremely difficult to observe in this material. On the other hand, calculations show that positrons are a good probe of the Cu-O layers in Tl2Ba2CaCu2O3.