Abstract
We report a ${}^{93}$Nb nuclear magnetic resonance (NMR) study on the noncentrosymmetric superconductor Re${}_{24}$Nb${}_{5}$. Below the superconducting temperature ${T}_{c}$($H$), the spin susceptibility probed by the ${}^{93}$Nb NMR Knight shift gradually decreases with lowering temperature, accompanied by the broadening of the resonance spectrum. Such behavior is commonly observed in the BCS-type superconductors. The ${}^{93}$Nb NMR spin-lattice relaxation rate (1/$T$${}_{1}$) shows a well-defined coherence peak just below ${T}_{c}$($H$), followed by a marked decrease with further decreasing temperature. Moreover, the 1/$T$${}_{1}$ data in the superconducting state were found to obey a single exponential expression, yielding a nodeless gap $\ensuremath{\Delta}/{k}_{B}=10.3$ K. This value gives the ratio of $2\ensuremath{\Delta}/{k}_{B}{T}_{c}(H)=3.55$, that is almost identical with the value of 3.5 predicted from BCS theory. On these bases, we conclude that the noncentrosymmetric Re${}_{24}$Nb${}_{5}$ compound can be characterized as a weakly coupled BCS-type superconductor.
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