Muon knight shift study on the insulating and metallic states in Na-loaded zeolite low-silica X

It is known that the insulator-metal transition occurs upon loading guest Na atoms into cages of the zeolite low silica X (LSX). In this study, the metallic and insulating phases of this material were investigated by the muon spin rotation ( \(\mu \) $\mu$ SR) method. We succeeded in detecting the muon frequency shift \(K_\mu \) $K_{\mu }$ for the insulating and metallic phases in low temperatures, which was not observed in the previous \(^{23}\) ${}^{23}$ Na-NMR measurements. Contribution to \(K_\mu \) $K_{\mu }$ , which is proportional to the density of state at the Fermi energy, is deduced to be 18±2% of that in the bulk metallic Na.