Electronic Transport in Gadolinium Atomic-Size Contacts

We report on the fabrication, transport measurements, and density functional theory (DFT) calculations of atomic size contacts made out of gadolinium (Gd). Gd is known to have local moments mainly associated with $f$ electrons. These coexist with itinerant $s$ and $d$ bands that account for its metallic character. Here we explore whether and how the local moments influence electronic transport properties at the atomic scale. Using both Scanning Tunneling Microscope (STM) and lithographic Mechanically Controllable Break Junction (MCBJ) techniques under cryogenic conditions, we study the conductance of Gd when only few atoms form the junction between bulk electrodes made out of the very same material. Thousands of measurements shows that Gd has an average lowest conductance, attributed to an atom-size contact, below $\frac{2e^2}{h}$. Our DFT calculations for monostrand chains anticipate that the $f$ bands are fully spin polarized and insulating, and that the conduction may be dominated by $s$, $p$, and $d$ bands. DFT quantum transport calculations quantitatively reproduce the experimental results for zero bias and reveal that, while $s-p$ bands are dominant for transport, $d$ orbitals seem to have a relevant contribution in some cases.