title: 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/T1, in sodium loaded low-silica X (LSX) zeolite, Nan/Na12-LSX, for various loading levels of sodium atoms n across the metal-to-insulator crossover. For high loading levels of n ≥ 14.2, 1/T1T shows nearly temperature-independent behaviour between 10 K and 25 K consistent with the Korringa relaxation mechanism and the metallic ground state. As the loading levels decrease below n ≤ 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 the 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.
authors.affiliation: Laboratory for Applied Physics, Department of Electrical Engineering, Gunma College, National Institute of Technology, Toribamachi 580, Maebashi 371-8530, Gunma, Japan.
authors.forename: Mutsuo
authors.initials: M
authors.lastname: Igarashi
authors.affiliation: Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.|EN-FIST Centre of Excellence, Dunajska 156, 1000 Ljubljana, Slovenia.
authors.forename: Peter
authors.initials: P
authors.lastname: Jeglič
authors.affiliation: National Institute of Chemistry, Hajdrihova 19, 1001 Ljubljana, Slovenia.
authors.forename: Andraž
authors.initials: A
authors.lastname: Krajnc
authors.affiliation: Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
authors.forename: Rok
authors.initials: R
authors.lastname: Žitko
authors.affiliation: Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Osaka, Japan.
authors.forename: Takehito
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Department of Physics, Graduate School of Science, Osaka University, Toyonaka 560-0043, Osaka, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Nozue
authors.affiliation: Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.|Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia.
authors.forename: Denis
authors.initials: D
authors.lastname: Arčon