NMR study of electronic properties in Mo7Re13B and W7Re13B superconductors

Summary form only given. We report a study of the superconducting rhenium-based borides Mo₇Re₁₃B and W₇Re₁₃B by means of the ¹¹B nuclear magnetic resonance (NMR) spectroscopy. Superconducting behavior with transition temperatures of 8.3 K and 7 K for Mo₇Re₁₃B and W₇Re₁₃B respectively have been reported. In the present work, NMR results indicate that the B Fermi level density of states is not predominated by p bands and the s-character electrons are the main origin responsible for the observed Knight shift as well as the spin-lattice relaxation rate (1/T₁). We thus deduce the partial B 2s Fermi level density of states, N_s(E_F), for both materials from 1/T₁ analysis. Universally small N_s(E_F) are found in these compounds, similar to those observed in other rhenium-based superconducting borides such as Re₇B₃ and Re₃B.