Metal to insulator transitions in clusters

Area of Science:

• * Physics and Chemistry of Nanomaterials
• * Quantum Mechanics and Electronic Structure

Background:

• * Traditional metallicity definition (finite density of states at Fermi energy) is unsuitable for finite-size systems like clusters.
• * Discrete energy levels in clusters necessitate a revised approach to defining metallic properties.

Purpose of the Study:

• * To propose and validate an alternative criterion for metallicity in atomic clusters.
• * To investigate the electronic band gaps of various metal cluster families using experimental data.

Main Methods:

• * Utilizing experimental photoelectron spectroscopy data of anionic clusters.
• * Analyzing the band gaps (energy difference between occupied and unoccupied states) relative to the Kubo band gap (delta).

Main Results:

• * Monovalent clusters generally exhibit band gaps smaller than delta, following shell structure patterns, with exceptions for shell closures or symmetry.
• * Mercury clusters show a clear insulator-to-metal transition with increasing size.
• * Other bivalent metals (Zn, Mg) and complex clusters (Al, transition metals) display more intricate behaviors.

Conclusions:

• * The proposed criterion (band gap ≤ delta) effectively identifies metallicity in clusters.
• * Cluster metallicity is size-dependent and influenced by electronic shell structure, symmetry, and elemental properties.
• * The study provides insights into the electronic behavior of diverse metallic cluster systems.