NMR study of Nb-deficient effect in NbB$_{2}$

Observations of the Nb-deficiency enhanced superconducting temperature ($T_{C})$ in NbB$_{2}$ have been reported. In order to provide experimental information for this effect, we have carried out the nuclear magnetic resonance (NMR) study of Nb$_{1-x}$B$_{2}$ (x = 0, 0.13, 0.20, and 0.26) in the normal state. From both $^{11}$B and $^{93}$Nb NMR spin-lattice relaxation rates, we can deduce the B-2$p$ and Nb-3$d$ partial Fermi-level density of states (DOS) for each individual composition. The result indicates that the B-2$p$ and Nb-3$d$ partial Fermi-level DOS increase with Nb deficient level. Such a tendency is consistent with the trend of the superconducting temperature, revealing that the observed $T_{C}$ enhancement is strongly correlated to the increase of the Fermi-level DOS induced by the Nb deficiency.