The vortex matter in bulk type-II superconductors serves as a prototype system for studying the random pinning problem in condensed matter physics. Since the vortex lattice is embedded in an atomic lattice, small angle neutron scattering (SANS) is the only technique that allows for direct structural studies. In traditional SANS methods, the scattering intensity is a measure of the structure factor averaged over the entire sample. Recent studies in vortex physics have shown that it is highly desirable to develop a SANS technique which is capable of resolving the spatial inhomogeneities in the bulk vortex state. Here we report a novel slicing neutron diffraction technique using atypical collimation and an areal detector which allows for observing the three dimensional (3D) disorder of the vortex matter inside an as-grown Nb single crystal.
Simulation of X-ray diffraction in Mn$_x$Bi$_2$Te$_{3+x}$ epitaxic films
无序异质结构代表作为同系化合物的一部分的一般描述，例如铋硫属化物。在器件工程中，这些化合物的范德华外延在自旋电子学和量子计算中的应用是非常有前途的。结构分析方法对于控制和改善它们以薄膜形式的合成是必不可少的。最近，X射线工具已被提出用于无序异质结构的结构建模[arXiv：2107.12280]。在这里，我们进一步评估使用这些工具来研究化合物Mn $_x$ Bi $_2$ Te $_{3+x}$在掠入射区域的反射率曲线，以及在广角区域的厚度波动的影响。
DFT study of La$_2$Ce$_2$O$_7$: disordered fluorite vs pyrochlore structure
用\textit{ab initio}密度泛函理论（DFT）计算了镧铈氧化物（La $_2$ Ce $_2$ O $_7$）的晶体结构.通过比较它们的形成能，研究了类萤石和类辉石岩结构的相对稳定性。这些形成能表明烧绿石结构优于萤石结构，显然与基于实验中子和X射线衍射（XRD）的结论相矛盾。通过计算和比较一组不同有序和随机结构的XRD谱，我们表明烧绿石结构与衍射实验是一致的。基于这些原因，我们建议烧绿石结构作为La $_2$ Ce $_2$ O $_7$的基态晶体结构。%，我们表明，在这项工作中考虑的结构，烧绿石的几何形状显然是有利的无序萤石的几何形状。
