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≈𝐺0=2𝑒2ℎ, 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 𝐺0. 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 T. 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 O2 molecules attached close to the contact produce 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 sizable response to a magnetic field can be built by combining noble metals and magnetically active molecular systems. [Full Article]
