A SYMMETRY BASED STUDY OF POSITRON-ANNIHILATION SPECTRA

We describe a method for off-line analysis of spectra measured by two- dimensional angular correlation of annihilation radiation (2D-ACAR) po sitron spectroscopy. The method takes into account, at all its stages, two salient data features: the piecewise constant discretization of t he 2D physical momentum distribution into square pixels, performed by the setup, and the occurrence of a characteristic 2D projected symmetr y of the positron-electron pair momentum distribution. Several validat ing criteria are derived which secure significantly increased reliabil ity of the output. The method is tested on 2D-ACAR spectra measured on (R)Ba2Cu3O7-delta (R123; R = Y, Dy) single crystals. It resolves ridg e Fermi surfaces (Fs) up to 3rd Umklapp components on both kinds of R1 23 spectra. Moreover, on a c-axis-projected Y123 spectrum, measured at 300 K, it resolves a small but clear signature of the pillbox Fs at t he S point of the first Brillouin zone as well.