Electron vortex beams generated by a transmission electron microscope (TEM) are employed to study magnetic properties of an impurity often embedded in materials. Compared to the optical wave, a higher spatial resolving power of electron waves enables the detection of impurities on the nanoscale. Here, we investigate theoretically the interaction of the twisted electrons and the magnetic impurity in which the magnetic dipole moment is taken as a demonstration element. In addition to the usual optical phase, the inhomogeneous vector potential generated by the magnetic dipole moment makes an additional contribution to the intrinsic orbital angular momentum of the twisted electrons, resulting in a dipole-dependent Gouy phase shift. By interfering the outgoing twisted electron beam with a reference cylindrical wave, one can determine the magnitude and orientation of the magnetic dipole directly via the rotational and deformed interference pattern. Furthermore, the pattern is shown to be sensitive to the width of the beam in the focal plane, which provides an effective way to reveal the influence of impurities on the twisted electrons more intuitively and distinctly. The obtained results demonstrate the usefulness of the twisted electron beams for probing the nanoscale magnetism of impurity by TEM, while the proposed model provides the conceptual basis for future developments of the TEM method.

中文翻译：

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使用电子涡旋束检测磁性杂质

由透射电子显微镜（TEM）产生的电子涡旋束用于研究通常嵌入材料中的杂质的磁性能。与光波相比，电子波具有更高的空间分辨能力，可以检测纳米级的杂质。在这里，我们从理论上研究了扭曲电子与以磁偶极矩为演示元素的磁性杂质的相互作用。除了通常的光学相位外，由磁偶极矩产生的不均匀矢量电势还对扭曲电子的固有轨道角动量做出了额外贡献，从而导致了偶极子相关的Gouy相移。通过用参考圆柱波干扰出射的扭曲电子束，可以通过旋转和变形的干涉图直接确定磁偶极子的大小和方向。此外，显示出该图案对焦平面中的电子束宽度敏感，这提供了一种有效的方式来更直观和清楚地揭示杂质对扭曲电子的影响。所得结果证明了扭曲电子束对于通过TEM探测杂质的纳米级磁性的有效性，而所提出的模型为TEM方法的未来发展提供了概念基础。这提供了一种更直观，更清晰地揭示杂质对扭曲电子的影响的有效方法。所得结果证明了扭曲电子束对于通过TEM探测杂质的纳米级磁性的有效性，而所提出的模型为TEM方法的未来发展提供了概念基础。这提供了一种更直观，更清晰地揭示杂质对扭曲电子的影响的有效方法。所得结果证明了扭曲电子束对于通过TEM探测杂质的纳米级磁性的有效性，而所提出的模型为TEM方法的未来发展提供了概念基础。