Comparative NMR study of copper-based intermetallics with ZrCuSiAs-type structure

The electronic characteristics of ZrCuGe₂, ZrCuSi₂, and HfCuSi₂ are systematically investigated using ⁶³Cu NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times on each individual compound have been identified. We found that the observed electric field gradient is consistent with the covalent bonding nature within the Cu atomic layers. The Knight shifts together with relaxation rates provide a measure of Cu d partial Fermi-level density of states, N_d(E_F). Universally small N_d(E_F) was found in all studied materials, suggests that the Cu d states are well below the Fermi energy and therefore the characteristic electronic structure near E_F is primarily of sp type. We further pointed out that the low N_d(E_F) value is an important factor for the lack of superconductivity in these Cu-based intermetallics within the ZrCuSiAs-type structure.