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 Cu₂N 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.

由于各向异性晶体场，吸附在表面上的磁性原子的轨道角矩通常被淬灭。由于自旋轨道耦合，轨道力矩的剩余部分通常描绘出电子自旋的取向。这两种效应将基于这些原子的信息处理的范围实际上限制为仅一个磁性自由度：自旋。在这项工作中，我们获得了对单个原子的自旋和轨道自由度的独立访问权，从而激发和探测每个时刻的激发。通过配位一个单一的Fe原子在Cu ₂的氮原子位点上在N晶格下，我们实现了一个单原子系统，该系统具有大的零场分裂-表面上的Fe原子报道的最大分裂-且非淬火的单轴轨道矩接近自由原子的值。我们通过尖端和Fe原子之间的单电子隧穿事件证明了轨道力矩的完全反转，该过程由带电的虚拟状态介导，并且使自旋保持不变。我们使用密度泛函理论和第一性原理多重计算来证实这些结果，证明了对单个原子系统中自旋和轨道自由度的独立控制。