Gamma-ray Compton profiles of copper and nickel

Te¹²³ᵐ 160-keV γ rays were used to measure the Compton profiles of fcc copper and nickel single crystals in the [100], [110], and [111] directions. The differences in the profiles in the various directions are only on the order of 1% but still clearly show the presence of d-type bonds in the [110] directions. Comparison of copper and nickel shows that the d bonding is quite similar in that the high-momentum anisotropy is the same in both systems. The reduction in the s-d band separation in going from copper to nickel is expected to explain the differences in the low-momentum anisotropy (free-electron contribution). Although our experimental resolution is too poor to clearly resolve details as sharp as the necks, our data for copper have the trend expected from such necks. The profiles and the anisotropy are expected to provide the first stringent test for d-like wave functions in these systems.