A-axis projected electron-positron-momentum density and positron-annihilation spectra in YBa₂Cu₃O₇-x

P. Pankaluoto, Northeastern University
A. Bansil, Northeastern University
L. C. Smedskjaer, Argonne National Laboratory
P. E. Mijnarends, Delft University of Technology

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Originally published in Physical Review B v.50 (1994): 6408-6415. DOI: 10.1103/PhysRevB. 50.6408

Abstract

We present and discuss theoretical and experimental a-axis-projected two-dimensional angular correlation of annihilation radiation (2D-ACAR) spectra from YBa₂Cu₃O₇₋ₓ. The experiment involved an untwinned metallic single crystal of YBa₂Cu₃O_6.9 at room temperature. The calculations have been carried out within the conventional first-principles band-theory framework based on the local-density approximation; the positron state is treated in the independent-particle model. After the as-observed 2DACAR spectrum is corrected for an isotropic background, a good accord is found between not only the overall shape but also the fine structure in the measured and computed spectra, some discrepancies not-withstanding. Extensive analysis shows that the experimental spectrum clearly contains the signature of the electron ridge Fermi surface (FS) arising from Cu-O chains in the first Brillouin zone. Also the first and second Umklapp images of the ridge FS at higher momenta are in substantial accord with theoretical predictions. These results suggest that the electron states in Y123 are not localized, at least not strongly, along the c direction.