Coherent Scattering with Twisted X-rays

Our research also extends to the use of coherent scattering and diffractive imaging with twisted X-rays. Twisted X-rays, or X-ray vortex beams, possess orbital angular momentum, providing unique capabilities for probing the structural and electronic properties of materials at the nanoscale. These twisted beams enable us to explore chirality and angular momentum transfer in materials, offering new insights into complex material behaviors and interactions. By combining twisted X-rays with our advanced diffractive imaging techniques, we can achieve unparalleled resolution and sensitivity in characterizing defects and other nanoscale features. This innovative approach allows us to study the intricate details of material structures and their evolution under various conditions, further advancing our understanding and control of material properties.

A major drawback of conventional methods of microscopy and imaging is that they require focusing lenses or apertures with precision comparable to the desired spatial resolution. Conversely, a different strategy is provided by resonant x-ray coherent diffractive imaging (CDI). An picture is created in CDI by numerically inverting the diffraction pattern created when a coherent x-ray beam is scattered from a sample. In this case, the greatest spatial frequencies found in the x-ray diffraction pattern limit the spatial resolution rather than the optical elements. Near electronic resonances, CDI provides elemental selectivity and can provide three-dimensional information. It enables high spatial resolution quantitative imaging of huge regions when paired with ptychographic techniques.

With the advent of twisted X-rays possessing an infinite topological charge, new opportunities in helical dichroic CDI became possible. These twisted X-rays, distinguished by their helical wavefronts, interact specifically with the electrical and magnetic structures of materials, providing improved sensitivity and contrast in magnetic CDI. This works especially well for visualizing intricate magnetic domains and textures. Equation below shows the modified scattering amplitude for twisted x-rays which implies a change in the scattering cross-section from the crystalline material.

Figure 1 below shows the different ways that chirality can appear in different order parameter spaces in ferroics: multiferroic, ferroelectric polarization texture, and structural lattice distortions. These systems’ diverse shapes and textures provide insight into the deep physical mechanisms that underlie multiferroic activity. One important characteristic of these materials is chirality, or the absence of mirror symmetry, which can result in unique physical features. For examining these chiral structures, twisted X-rays, or X-rays with orbital angular momentum, can offer a special kind of investigation instrument. Depending on the chirality of the material, twisted X-rays interact with it differently due to their helical phase fronts. Conventional X-rays cannot discriminate between left-handed and right-handed structures in the material; however, this interaction can. Because twisted X-rays are so sensitive to chirality, they are a great option to investigate the chiral characteristics of multiferroics. With the potential to provide new light on the coupling mechanisms between the electric and magnetic orders in these materials, they can be utilized to map out the electric polarization patterns, structural distortions, and spin magnetic tubes in unprecedented depth.[1]

Figure 1 Chirality in Multiferroics

  1. Nimish P. Nazirkar, Xiaowen Shi, Jian Shi, Moussa N’Gom, Edwin Fohtung; Coherent diffractive imaging with twisted X-rays: Principles, applications, and outlook. Appl. Phys. Rev. 1 June 2024; 11 (2): 021302.