Metallic properties of magnesium point contacts

TL;DR

This study investigates the conductance and stability of magnesium atomic contacts, revealing a shell effect at room temperature, the absence of single-atom contacts, and a dominant quantum conductance peak at low temperatures, combining experiments and first-principles calculations.

Contribution

It provides new experimental data on Mg atomic contacts and theoretical insights into their electronic properties, highlighting the role of atomic coordination and temperature effects.

Findings

Room temperature conductance histograms show a non-atomic shell effect.

Single-atom contacts are absent at room temperature.

At low temperatures, conductance is dominated by a single channel.

Abstract

We present an experimental and theoretical study of the conductance and stability of Mg atomic-sized contacts. Using Mechanically Controllable Break Junctions (MCBJ), we have observed that the room temperature conductance histograms exhibit a series of peaks, which suggests the existence of a shell effect. Its periodicity, however, cannot be simply explained in terms of either an atomic or electronic shell effect. We have also found that at room temperature, contacts of the diameter of a single atom are absent. A possible interpretation could be the occurrence of a metal-to-insulator transition as the contact radius is reduced, in analogy with what it is known in the context of Mg clusters. However, our first principle calculations show that while an infinite linear chain can be insulating, Mg wires with larger atomic coordinations, as in realistic atomic contacts, are alwaysmetallic. Finally, at liquid helium temperature our measurements show that the conductance histogram is dominated by a pronounced peak at the quantum of conductance. This is in good agreement with our calculations based on a tight-binding model that indicate that the conductance of a Mg one-atom contact is dominated by a single fully open conduction channel.