Complete reversal of the atomic unquenched orbital moment by a single electron

TL;DR

This paper demonstrates the full reversal of an unquenched atomic orbital moment in a single Fe atom on a surface through a single-electron tunneling event, enabling independent control of spin and orbital states.

Contribution

It introduces a method to reversibly control the orbital moment of a single atom independently of its spin, using electron tunneling.

Findings

Achieved the largest zero-field splitting for Fe atoms on surfaces.

Reversed the orbital moment via a single-electron tunneling event.

Confirmed results with density functional theory and multiplet calculations.

Abstract

The orbital angular moment of magnetic atoms adsorbed on surfaces is often quenched as a result of an anisotropic crystal field. Due to spin-orbit coupling, what remains of the orbital moment typically delineates the orientation of the electron spin. These two effects limit the scope of information processing based on these atoms to essentially only one magnetic degree of freedom: the spin. In this work, we gain independent access to both the spin and orbital degrees of freedom of a single atom, inciting and probing excitations of each moment. By coordinating a single Fe atom atop the nitrogen site of the Cu$_2$N lattice, we realize a single-atom system with a large zero-field splitting--the largest reported for Fe atoms on surfaces--and an unquenched uniaxial orbital moment that closely approaches the free-atom value. We demonstrate a full reversal of the orbital moment through a single-electron tunneling event between the tip and Fe atom, a process that is mediated by a charged virtual state and leaves the spin unchanged. These results, which we corroborate using density functional theory and first-principles multiplet calculations, demonstrate independent control over the spin and orbital degrees of freedom in a single-atom system.