Electron momentum distribution and Fermi surface of vanadium studied by positron annihilation

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Abstract
Two-dimensional (2D) angular correlation of positron annihilation radiation (ACPAR) N(py,pz) has been measured for four orientations (100), (110), (111) and (112) in vanadium. Theoretical band-structure calculations of N(py,pz) in V are performed in the independent-particle model by taking into account the positron wavefunction but leaving out e+-e- many-body correlations. A detailed analysis of the experimental and theoretical results is carried out by using different approaches. Although the agreement between experiment and theory is good in general, some discrepancies are also observed. These differences provide valuable information about the nature of the e+-e- many-body correlations which appear to be anisotropic and energy-dependent in nature. Effects of the Fermi surface (FS) of vanadium on the ACPAR curves are observed in the p and k space and the results allow a determination of the dimensions of the FS. The possibility of a neck (along Gamma N) connecting the N-centred ellipsoid and multiply connected 'jungle-gym' arms in the FS of vanadium is examined and it is concluded that the present experimental data do not support the existence of such a neck.