Study of the Fermi surface of molybdenum and chromium via positron annihilation experiments

Abstract

A quantitative mapping of the Fermi surface (FS) of molybdenum and chromium was sought by modelling the three-dimensional k -space occupancy with a small number of parameters which were determined by a least-squares fit to the two-dimensional angular correlation of the electron–positron annihilation radiation (2D-ACAR) data subjected to a Lock–Crisp–West (LCW) transformation. The resulting FS topology of molybdenum, unlike what was assumed in previous 2D-ACAR studies, does not support the nesting of its two main FS sheets. In the case of chromium, although the overall discrepancy with the FS expected from the theory is larger, the difference in shape between the same two FS sheets is of lesser extent. According to this analysis the ratio of the electron Fermi volume to the hole Fermi volume is found to deviate from unity, the value expected for compensated metals, for both materials. We suggest that these discrepancies might be due to positron wave function and/or electron–positron many-body distortions not predicted by the theory.