Nb93nuclear magnetic resonance and relaxation inNb3Sn,Nb3Al, andNb3Sb

The high-temperature superconductors ${\mathrm{Nb}}_3$Sn and ${\mathrm{Nb}}_3$Al and the low-temperature superconductor ${\mathrm{Nb}}_3$Sb have been investigated by ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ nuclear magnetic resonance and spin-lattice relaxation-time $T_1$ measurements. The relaxation-time results combined with electronic-heat-capacity results indicate that ${\mathrm{Nb}}_3$Sn and ${\mathrm{Nb}}_3$Al have similar densities of states at the Fermi level in the $\delta$ and $\pi$ subbands, whereas ${\mathrm{Nb}}_3$Sn has a much larger density of states at $E_F$ in the $\sigma$ subband. ${\mathrm{Nb}}_3$Sb is a low density-of-states material. Large enhancements of ${\left(T_{1}T\right)}^{-1\mathrm{}}$ (∼300%) are found for $T\simeq T_c$ in ${\mathrm{Nb}}_3$Al and ${\mathrm{Nb}}_3$Sn. The dependence of ${\left(T_{1}T\right)}^{-1\mathrm{}}$ on $\frac{(T-T_c)}{T_c}$ suggests that highly anisotropic pair fluctuations exist well above $T_c$.