Nuclear magnetic resonance investigation of superconducting and normal state Nb₃Sn

The superconductor Nb 3 Sn has important applications for construction of very high-field superconducting magnets. In this work we investigate its microscopic electronic structure with 93 Nb nuclear magnetic resonance (NMR). The high-quality Nb 3 Sn powder sample was studied in both 3.2 T and 7 T magnetic fields in the temperature range from 4 K to 300 K. From measurement of the spectrum and its theoretical analysis, we find evidence for anisotropy despite its cubic crystal structure. Magnetic alignment of the powder grains in the superconducting state was also observed. The Knight shift and spin-lattice relaxation rate, T 1 − 1 , were measured and the latter compared with BCS theory for the energy gap Δ ( 0 ) = 2.7 ± 0.3 k B T c at 3.2 T and Δ ( 0 ) = 2.33 ± 0.07 k B T c at 7 T, indicating suppression of the order parameter by magnetic field.