In order to understand superconductivity in A15 structure compounds, two-dimensional angular correlation of positron annihilation radiation (2D-ACPAR) has been measured in a single crystal of Nb3Sn for three orientations (100), (110) and (210). Also band-structure calculations using the self-consistent linear muffin-tin orbital (LMTO) method are performed for Nb3Sn. A comparison between experiment and theory at different stages of the analysis shows in general good agreement. The measured momentum distributions are folded to the crystal momentum space, followed by a three-dimensional reconstruction of the occupation density. The extracted Fermi surfaces (FS) reveal the presence of a cube-shaped hole pocket, responsible for the high superconducting transition temperature (Tc=18 K), which seems to be a feature of all FS of high-Tc A15 compounds.
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