Evolution of the density of states at the Fermi level across the metal-to-insulator crossover in alkali doped zeolite

Abstract

We report a systematic nuclear magnetic resonance investigation of the ${}^{23}$Na spin-lattice relaxation rate, $1/T_1$, in sodium loaded low-silica X (LSX) zeolite, Na${}_n$/Na${}_{12}$-LSX, for various loading levels of sodium atoms $n$ across the metal-to-insulator crossover. For high loading levels of $n\ge 14.2$, $1/T_{1}T$ shows nearly temperature-independent behavior between 10 K and 25 K consistent with the Korringa relaxation mechanism and metallic ground state. As the loading levels decrease below $n\le 11.6$, the extracted density of states (DOS) at the Fermi level sharply decreases, although a residual DOS at Fermi level is still observed even in samples that lack the metallic Drude-peak in the optical reflectance. The observed crossover is a result of a complex loading-level dependence of electric potential felt by the electrons confined to zeolite cages, where the electronic correlations and disorder both play an important role.

7 pages, 5 figures

References in corpus (3)

• ${}^{75}$As NMR studies of superconducting LaO${}_{0.9}$F${}_{0.1}$FeAs
• Theoretical Studies of Superconductor-Insulator Transitions
• Repulsive vs. attractive Hubbard model: transport properties and spin-lattice relaxation rate

Cited by in corpus (2)

• Thermally Activated Motion of Sodium Cations in Insulating Parent Low-Silica X Zeolite
• Metallic State in Rubidium-Loaded Low-Silica X zeolite