Field Gradient Induced by Organic Intercalation of Superconducting Layered Dichalcogenides

Magnetic-resonance observations of niobium nuclei in both the layered dichalcogenide Nb${\mathrm{S}}_2$ and the associated intercalation complex Nb${\mathrm{S}}_2$ ${\mathrm{}\left(\mathrm{pyridine}\right)\mathrm{}}_{1/2}$ yield different electric field gradients in the two compounds. At 4.2°K, $\frac{e^2\mathrm{qQ}}{h}=60\mathrm{}$ MHz in Nb${\mathrm{S}}_2$ and 46 MHz in Nb${\mathrm{S}}_2$ ${\mathrm{}\left(\mathrm{Py}\right)\mathrm{}}_{1/2}$. The difference is shown to arise from the conduction-electron term. It may result from charge transfer between the organic molecules and the conduction band of the layered dichalcogenide, or from redistribution of electrons between two overlapping conduction bands. The lattice sum for the field gradient is shown to be derived almost entirely from intralayer charges.