Signature of Fermi surface jumps in positron spectroscopy data

A subtractionless method for solving Fermi surface sheets (FSS), from measu red n-axis-projected momentum distribution histograms by two-dimensional an gular correlation of the positron-electron annihilation radiation (2D-ACAR) technique, is discussed. The window least squares statistical noise smooth ing filter described by Adam et al. [Nucl.Instr. & Meth. A 337 (1993) 188] is first refined such that the window free radial parameters (WRP) are opti mally adapted to the data. In an ideal single crystal, the specific jumps i nduced in the WRP distribution by the existing Fermi surface jumps yield st raightforward information on the resolved FSS. In a real crystal, the smear ing of the derived WRP optimal values, which originates from positron annih ilations with electrons at crystal imperfections, is ruled out by median sm oothing of the obtained distribution, over symmetry defined stars of bins. The analysis of a gigacount 2D-ACAR spectrum, measured on the archetypal hi gh-T-c compound YBa2Cu3O7-delta at room temperature, illustrates the method . Both electronic FSS, the ridge along Gamma X direction and the pillbox ce ntered at the S point of the first Brillouin zone, are resolved. (C) 1999 E lsevier Science B.V. All rights reserved.