Normal-state properties of the antiperovskite oxide Sr3−xSnO revealed by Sn119 -NMR

We have performed $¹¹⁹\mathrm{Sn}$-NMR measurements on the antiperovskite oxide superconductor ${\mathrm{Sr}}_{3\ensuremath{-}x}\mathrm{SnO}$ to investigate how its normal state changes with the Sr deficiency. A two-peak structure was observed in the NMR spectra of all the measured samples. This suggests that the phase separation tends to occur between the nearly stoichiometric and heavily Sr-deficient ${\mathrm{Sr}}_{3\ensuremath{-}x}\mathrm{SnO}$ phases. The measurement of the nuclear spin-lattice relaxation rate $1/{T}₁$ indicates that the Sr-deficient phase shows a conventional metallic behavior due to the heavy hole doping. In contrast, the nearly stoichiometric phase exhibits unusual temperature dependence of $1/{T}₁$, attributable to the presence of a Dirac-electron band.