  $^{195}$Pt-NMR measurements of Pt nanoparticles with a mean diameter of 4.0
nm were performed in a high magnetic field of approximately $\mu_0 H = 23.3$ T
to investigate the low-temperature electronic state of the nanoparticles. The
characteristic temperature $T^*$, below which the nuclear spin-lattice
relaxation rate $1/T_1$ deviates from the relaxation rate of the bulk, shows a
magnetic-field dependence. This dependence supports the theoretical prediction
of the appearance of discrete energy levels.
