Conductance of atomic size contacts of Ag and Au at high magnetic fields

TL;DR

This study investigates the conductance of single-atom Au and Ag contacts under high magnetic fields, revealing that residual molecules induce spin-polarized currents causing conductance decreases, suggesting potential for magnetic field-responsive atomic conductors.

Contribution

It demonstrates that residual molecules near noble metal atomic contacts induce spin-polarized currents, affecting conductance under high magnetic fields, which is a novel insight into atomic-scale magnetotransport.

Findings

Conductance decreases up to 15% at 20 T in many Au contacts.

Pure Ag and Au show weak field dependence of conductance.

Residual O₂ molecules induce spin-polarized currents affecting conductance.

Abstract

Electronic conduction at the atomic scale can be described by Landauer's formalism. In single atom point contacts of noble metals like Au and Ag, there is just one channel open between both electrodes and the conductance is very close to the quantum of conductance $G \approx G_0=\frac{2e^2}{h}$, with the factor of two coming from spin degeneracy. The magnetoconductivity of atomic size contacts has been studied for numerous systems, unveiling local Kondo screening, magnetic order and spin-polarized currents. However, these have been mostly performed in elements with multiple open conduction channels where $G$ differs from $G_0$. The realization of a magnetically active conductor with a single open channel remains difficult to achieve. Here we present measurements of the electronic conductance of single channel Au and Ag atomic-size contacts in magnetic fields up to 20 Tesla. We observe a decrease in $G$ which goes up to about 15% in many Au contacts at 20 T. We perform calculations and find that pure Ag and Au do not present a strong field dependence of $G$, in agreement with previous results at smaller magnetic fields. We also find, however, that residual O$_2$ molecules attached close to the contact produce an an induced spin-polarized current, which leads to a decrease in $G$. We discuss the role of the magnetic response of the electrodes in the jump to contact. Our results suggest that single channel atomic size conductors with a sizeable response to a magnetic field can be built by combining noble metals and magnetically active molecular systems.