Probing magnetic interactions between Cr adatoms on the Bi2Pd superconductor

Abstract

We show that the magnetic ordering of coupled atomic dimers on a superconductor is revealed by their intra-gap spectral features. Chromium atoms on the superconductor Bi2Pd surface display Yu-Shiba-Rusinov bound states, detected as pairs of intra-gap excitations in tunneling spectra. By means of atomic manipulation with a scanning tunneling microscope's tip, we formed Cr dimers with different arrangements and found that their intra-gap features appear either shifted or split with respect to single atoms. The spectral variations reveal that the magnetic coupling of the dimer changes between ferromagnetic and antiferromagnetic depending on its disposition on the surface, in good agreement with density functional theory simulations. The striking qualitative difference between the two magnetic orderings proves that intra-gap state spectroscopy gives an accurate information of exchange interactions on the atomic scale.