利用携带轨道角动量的散射X射线束的二向色性探测反铁磁实空间构型
Antiferromagnetic real-space configuration probed by dichroism in scattered x-ray beams with orbital angular momentum
AI总结：
本研究利用携带轨道角动量的X射线束，在含拓扑缺陷的人工反铁磁体中发现了与光束螺旋性耦合的新型圆二向色效应，可探测反铁磁基态实空间构型，为软X射线表征提供了新途径。
摘要：
携带轨道角动量（OAM）的X射线束是X射线表征技术中极具前景的工具。携带OAM的光束具有螺旋性——即随方位角变化的相位——这会产生光场梯度。利用OAM光束的螺旋性可以探测新的材料性质。本研究中，我们在含拓扑缺陷的人工反铁磁体的共振衍射中演示了一种新型二向色效应。我们发现，散射后的OAM光束在反铁磁布拉格峰处存在圆二向色性，其符号与光束的螺旋性耦合，这一特性揭示了反铁磁基态的实空间构型。人工反铁磁体的热循环可改变其基态，这一点可通过圆二向色性的符号反转得到印证。该成果是利用X射线轨道角动量的软X射线光谱表征技术的首批演示之一。这种依赖螺旋性的圆二向色性证明了利用OAM光束探测物质的潜力，这种探测方式是现有X射线技术无法实现的。
英文摘要：
X-ray beams with orbital angular momentum (OAM) are a promising tool for x-ray characterization techniques. Beams with OAM have a helicity--an azimuthally varying phase--which leads to a gradient of the light field. New material properties can be probed by utilizing the helicity of an OAM beam. Here, we demonstrate a novel dichroic effect in resonant diffraction from an artificial antiferromagnet with a topological defect. We found that the scattered OAM beam has circular dichroism at the antiferromagnetic Bragg peak whose sign is coupled to its helicity, which reveals the real-space configuration of the antiferromagnetic ground state. Thermal cycling of the artificial antiferromagnet can change the ground state, as indicated by reversal of the sign of circular dichroism. This result is one of the first demonstrations of a soft x-ray spectroscopy characterization technique utilizing the OAM of x-rays. This helicity-dependent circular dichroism exemplifies the potential to utilize OAM beams to probe matter in a way that is inaccessible using currently available x-ray techniques.
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