编译 | 李言
Science, 4 MAR 2022, VOL 375, ISSUE 6584
《科学》2022年3月4日，第375卷，6584期
物理学 Physics
A synthetic monopole source of Kalb-Ramond field in diamond
金刚石中观察到Kalb-Ramond场张量磁单极子
▲ 作者：MO CHEN, CHANGHAO LI, GIANDOMENICO PALUMBO, YAN-QING ZHU , NATHAN GOLDMAN , AND PAOLA CAPPELLARO
▲ 链接：
https://www.science.org/doi/10.1126/science.abe6437
▲ 摘要
磁单极子在从电磁到拓扑物质的物理领域中发挥着核心作用。弦理论将电动力学的常规矢量规范场推广为张量规范场，并预测了更多奇异张量磁单极子的存在。
在此，我们报告通过在由金刚石中单个固态缺陷的自旋自由度定义的四维参数空间中合成张量磁单极子。利用两种互补的方法，通过测量张量单极子的量子化拓扑电荷和发射的Kalb-Ramond场，对其进行了表征。
通过引入一个打破手征对称性的虚构外场，我们观察到了一个有趣的光谱跃迁，其特征是受镜像对称性保护的光谱环。我们的工作证明了模拟受弦理论启发的奇异拓扑结构的可能性。
▲ Abstract
Magnetic monopoles play a central role in areas of physics that range from electromagnetism to topological matter. String theory promotes conventional vector gauge fields of electrodynamics to tensor gauge fields and predicts the existence of more exotic tensor monopoles. Here, we report the synthesis of a tensor monopole in a four-dimensional parameter space defined by the spin degrees of freedom of a single solid-state defect in diamond. Using two complementary methods, we characterized the tensor monopole by measuring its quantized topological charge and its emanating Kalb-Ramond field. By introducing a fictitious external field that breaks chiral symmetry, we further observed an intriguing spectral transition, characterized by spectral rings protected by mirror symmetries. Our work demonstrates the possibility of emulating exotic topological structures inspired by string theory.
Topological magnon band structure of emergent Landau levels in a skyrmion lattice
斯格明子晶格的拓扑磁振子带结构
▲ 作者：T. WEBER, D. M. FOBES, J. WAIZNERP. STEFFENS et al.
▲ 链接：
https://www.science.org/doi/10.1126/science.abe4441
▲ 摘要
自旋激发在拓扑非平凡磁序上的运动显示出一种偏转，类似于洛伦兹力对轨道磁场中带电粒子的影响。我们使用极化非弹性中子散射来研究硅化锰材料中的斯格明子管晶格中磁振子（即玻色子集体自旋激发）的传播。
对于垂直于斯格明子晶格的波矢，磁振子谱与精细间隔的出射朗道能级的形成一致，这是用来解释斯格明子晶格非琐细拓扑缠绕的虚拟磁场的特征。
这证明了在倒易空间中存在拓扑磁振子能带结构，这是由磁序的非平凡实空间拓扑产生的。
▲ Abstract
The motion of a spin excitation across topologically nontrivial magnetic order exhibits a deflection that is analogous to the effect of the Lorentz force on an electrically charged particle in an orbital magnetic field. We used polarized inelastic neutron scattering to investigate the propagation of magnons (i.e., bosonic collective spin excitations) in a lattice of skyrmion tubes in manganese silicide. For wave vectors perpendicular to the skyrmion tubes, the magnon spectra are consistent with the formation of finely spaced emergent Landau levels that are characteristic of the fictitious magnetic field used to account for the nontrivial topological winding of the skyrmion lattice. This provides evidence of a topological magnon band structure in reciprocal space, which is borne out of the nontrivial real-space topology of a magnetic order.
Breakdown of topological protection by cavity vacuum fields in the integer quantum Hall effect
整数量子霍尔效应中腔真空场对拓扑保护的破坏
▲ 作者：FELICE APPUGLIESE, JOSEFINE ENKNER, GIAN LORENZO PARAVICINI-BAGLIANI et al.
▲ 链接：
https://www.science.org/doi/10.1126/science.abl581
▲ 摘要
利用空腔电磁谐振器的真空场来控制材料的电子性质是凝聚态物理研究的前沿之一。
我们发现，亚波长分裂环谐振腔中真空场涨落的增强极大影响了最典型的量子保护者之一，即高迁移率二维电子气体中的量子霍尔电子输运。
用长空腔介导的电子跳变解释了观测到的整数量子霍尔效应拓扑保护失效，在此过程中，光物质耦合哈密顿量的*共反**振项在真空涨落诱导下发展为有限电阻率。
我们的实验平台可用于任何二维材料，为利用真空场工程来操纵物质中的电子相提供了途径。
▲ Abstract
The prospect of controlling the electronic properties of materials via the vacuum fields of cavity electromagnetic resonators is emerging as one of the frontiers of condensed matter physics. We found that the enhancement of vacuum field fluctuations in subwavelength split-ring resonators strongly affects one of the most paradigmatic quantum protectorates, the quantum Hall electron transport in high-mobility two-dimensional electron gases. The observed breakdown of the topological protection of the integer quantum Hall effect is interpreted in terms of a long-range cavity-mediated electron hopping where the anti-resonant terms of the light-matter coupling Hamiltonian develop into a finite resistivity induced by the vacuum fluctuations. Our experimental platform can be used for any two-dimensional material and provides a route to manipulate electron phases in matter by means of vacuum-field engineering.
化学 Chemistry
Elongation and branching of α-olefins by two ethylene molecules
两个乙烯分子对α-烯烃的延伸和分支
▲ 作者：THOMAS DIETEL, FABIAN LUKAS, WINFRIED P. KRETSCHMER, AND RHETT KEMPE
▲ 链接：
https://www.science.org/doi/10.1126/science.abm5281
▲ 摘要
α-烯烃是生产塑料、医药、精细和散装化学品的重要原料。然而，廉价的原料乙烯选择性合成α-烯烃受到限制，因此，广泛应用的选择性合成α-烯烃受到人们的青睐。
在此，我们报告α-烯烃与两个乙烯分子的催化反应。第一个乙烯分子形成一个4-乙基分支，而第二个形成一个新的末端碳-碳双键（C2延伸）。
该反应的关键是开发出一种高活性和稳定的分子钛催化剂，能够进行极快的β-氢化物消除和转移。
▲ Abstract
α-Olefins are important starting materials for the production of plastics, pharmaceuticals, and fine and bulk chemicals. However, the selective synthesis of α-olefins from ethylene, a highly abundant and inexpensive feedstock, is restricted, and thus a broadly applicable selective α-olefin synthesis using ethylene is highly desirable. Here, we report the catalytic reaction of an α-olefin with two ethylene molecules. The first ethylene molecule forms a 4-ethyl branch and the second a new terminal carbon-carbon double bond (C2 elongation). The key to this reaction is the development of a highly active and stable molecular titanium catalyst that undergoes extremely fast β-hydride elimination and transfer.
天文学 Astronomy
Pebbles and sand on asteroid (162173) Ryugu: In situ observation and particles returned to Earth
小行星“龙宫”上的卵石和沙子:实地观察和带回地球的材料
▲ 作者：S. TACHIBANA, H. SAWADA, R. OKAZAKI et al.
▲ 链接：
https://www.science.org/doi/10.1126/science.abj8624
▲ 摘要
隼鸟2号探测器调查了碳质小行星“龙宫”。该任务进行了两次着陆作业，收集地表和由人工撞击暴露的地下材料样本。
我们展示了第二次着陆地点的图像，发现从撞击坑喷出的物质存在于样本位置。
两个着陆点的卵石表面呈现出从粗糙到光滑的形态变化，与“龙宫”的卵石相似，形状从准球形到扁平。这些样本于2020年12月6日返回地球。
在这项研究中，我们描述了返回样品中大于 5克的沙子和鹅卵石的形态。它们多样的颜色、形状和结构与观察到的“龙宫”材料一致; 我们认为它们是小行星的代表性样本。
▲ Abstract
The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu’s boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid.
地球科学 Geoscience
Soil microbiota as game-changers in restoration of degraded lands
土壤微生物群是退化土地恢复中的改变规则者
▲ 作者：OKSANA COBAN, GERLINDE B. DE DEYN, AND MARTINE VAN DER PLOEG
▲ 链接：
https://www.science.org/doi/10.1126/science.abe0725
▲ 摘要
土地退化降低了土壤功能，从而降低了土壤提供的产出质量。土壤水文功能对防治土壤退化和促进土壤恢复具有重要意义。
土壤微生物影响土壤水文，但土壤微生物在土壤形成和维持中的作用尚未得到重视。案例研究表明，土壤微生物在恢复土壤功能方面具有改变游戏规则的潜力。
本文综述了微生物在土地修复技术中的应用现状、土壤修复潜力最大的微生物类群、微生物对土壤物理性质的影响，并提出了退化土地的长期修复策略。
我们还强调需要推进生物物理景观相互作用这一新兴研究领域，以支持土壤-植物生态系统恢复。
▲ Abstract
Land degradation reduces soil functioning and, consequently, the services that soil provides. Soil hydrological functions are critical to combat soil degradation and promote soil restoration. Soil microorganisms affect soil hydrology, but the role of soil microbiota in forming and sustaining soil is not well explored. Case studies indicate the potential of soil microorganisms as game-changers in restoring soil functions. We review the state of the art of microorganism use in land restoration technology, the groups of microorganisms with the greatest potential for soil restoration, knowledge of the effect of microorganisms on soil physical properties, and proposed strategies for the long-term restoration of degraded lands. We also emphasize the need to advance the emerging research field of biophysical landscape interactions to support soil-plant ecosystem restoration practices.