Metallic State in Rubidium-Loaded Low-Silica X zeolite

TL;DR

This study demonstrates that rubidium clusters confined in low-silica X zeolite maintain their metallic properties, evidenced by NMR and resistivity measurements, challenging the expectation that quantum effects suppress metallicity at the nanoscale.

Contribution

The paper provides experimental evidence that rubidium clusters in zeolite frameworks retain metallic behavior, with enhanced density of states at the Fermi level, expanding understanding of alkali metal confinement effects.

Findings

Rubidium clusters exhibit Korringa behavior indicating metallicity.

Electrical resistivity measurements support the metallic state.

Enhanced density of states at the Fermi level compared to sodium cases.

Abstract

The ground state of alkali metals when the particle size decreases from bulk to nanometric atomic clusters is inevitably accompanied by quantum effects that can suppress their pristine metallic state. We demonstrate that the metallic nature of rubidium clusters confined and arrayed in the framework of insulating low-silica X zeolite is preserved. The $^{87}$Rb NMR spin-lattice relaxation assigned to rubidium clusters in supercages shows a Korringa behavior from 190~K down to 10~K, which is compatible with a macroscopic observation of low electrical resistivity. The density of states at the Fermi level is found to be enhanced compared to the analogous sodium case, consistent with a Holstein-Hubbard model of alkali-loaded zeolites.