矢量磁场中单原子电子自旋共振的调谐
Tuning Single-Atom Electron Spin Resonance in a Vector-Magnetic Field
摘要：
单自旋中心的自旋共振在化学结构分析、量子传感和量子相干操纵等方面具有巨大的应用潜力。这些实验的关键是一个二能级自旋系统的存在，其能量分裂可以通过施加磁场来选择。近年来，电子自旋共振（ESR）和扫描隧道显微镜（STM）的组合已被证明是一种检测表面上单个原子的磁性并实现亚$μ$ eV能量分辨率的技术。然而，到目前为止，所需的磁场的作用尚未阐明。在这里，我们进行单原子ESR上吸附在氧化镁（MgO）上的单个Fe原子，使用二维矢量磁场，以及在市售的STM的磁性STM尖端的局部字段。我们展示了如何通过优化磁场来大大提高ESR幅度，特别是在大的面内磁场中揭示增强的信号。此外，我们证明了从磁性STM尖端的杂散场是一个通用的工具。我们在这里使用它来更有效地驱动电子自旋，并通过采用尖端场扫描在恒定频率下进行ESR测量。最后，我们表明，它是可能的，只使用尖端场，在零外部磁场，这有望使这项技术可在许多现有的STM系统。
英文摘要：
Spin resonance of single spin centers bears great potential for chemical structure analysis, quantum sensing and quantum coherent manipulation. Essential for these experiments is the presence of a two-level spin system whose energy splitting can be chosen by applying a magnetic field. In recent years, a combination of electron spin resonance (ESR) and scanning tunneling microscopy (STM) has been demonstrated as a technique to detect magnetic properties of single atoms on surfaces and to achieve sub-$μ$eV energy resolution. Nevertheless, up to now the role of the required magnetic fields has not been elucidated. Here, we perform single-atom ESR on individual Fe atoms adsorbed on magnesium oxide (MgO), using a 2D vector magnetic field as well as the local field of the magnetic STM tip in a commercially available STM. We show how the ESR amplitude can be greatly improved by optimizing the magnetic fields, revealing in particular an enhanced signal at large in-plane magnetic fields. Moreover, we demonstrate that the stray field from the magnetic STM tip is a versatile tool. We use it here to drive the electron spin more efficiently and to perform ESR measurements at constant frequency by employing tip-field sweeps. Lastly, we show that it is possible to perform ESR using only the tip field, under zero external magnetic field, which promises to make this technique available in many existing STM systems.
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