翻译 | 李言
Science, 03 January 2020, Vol 367, Issue 6473
《科学》2020年1月3日，第367卷，6473期
物理学Physics
Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices量子反常霍尔超导体中马约拉纳手性模式的存在缺乏证据
作者：Morteza Kayyalha, Di Xiao, Ruoxi Zhang, Jaeho Shin, Jue Jiang, Fei Wang, Yi-Fan Zhao, et al
链接：
https://science.sciencemag.org/content/367/6473/64
摘要：
量子反常霍尔绝缘体与s波超导体结合被预言可以产生马约拉纳手性模式。
近期的一项实验将半整数量子化两端法电导平台解释为马约拉纳手性模式在毫米级量子反常霍尔超导样品上存在的证据。
然而，非马约拉纳机制也可以产生相似的结果，尤其是在无序样品中。在此，我们研究了在量子反常霍尔绝缘体与超导体之间有易于控制且透明表面的相似复合样品。
当样品处于量子反常霍尔状态且有序磁化时，总能观测到半整数量子化两端法电导平台。我们的实验为在量子反常霍尔超导样品中观测到的超导邻近效应提供了全面的认识，并表明在具有高透明性的表面的样品中，手性马约阿纳费米子不太可能导致半整数量子化电导平台。
Abstract
A quantum anomalous Hall (QAH) insulator coupled to an s-wave superconductor is predicted to harbor chiral Majorana modes. A recent experiment interprets the half-quantized two-terminal conductance plateau as evidence for these modes in a millimeter-size QAH-niobium hybrid device. However, non-Majorana mechanisms can also generate similar signatures, especially in disordered samples. Here, we studied similar hybrid devices with a well-controlled and transparent interface between the superconductor and the QAH insulator. When the devices are in the QAH state with well-aligned magnetization, the two-terminal conductance is always half-quantized. Our experiment provides a comprehensive understanding of the superconducting proximity effect observed in QAH-superconductor hybrid devices and shows that the half-quantized conductance plateau is unlikely to be induced by chiral Majorana fermions in samples with a highly transparent interface.
Evidence for dispersing 1D Majorana channels in an iron-based superconductor铁基超导体中一维马约拉纳通道分散的证据
作者：Zhenyu Wang, Jorge Olivares Rodriguez, Lin Jiao, Sean Howard, Martin Graham, G. D. Gu, Taylor L. Hughes, Dirk K. Morr, Vidya Madhavan
链接：
https://science.sciencemag.org/content/367/6473/104
摘要：
在凝聚态物理学中将马约拉纳费米子作为准粒子激发来实现的可能性令人兴奋。大多数研究都专注于马约拉纳束缚态；然而，马约拉纳态线性色散的传播也被预测了。
在此，我们报告了在铁基超导体FeSe0.45Te0.55中晶体畴壁（DWs）的扫描隧道光谱测量结果。通过移动了半个单位晶胞的晶格结构，我们定位了畴壁。
这些畴壁在超导能隙中具有有限的平坦态密度，这是一维线性色散模式的标志。在不处于拓扑阶段的相关超导体FeSe的畴壁中则没有这种特征。我们的综合数据与在近似拓扑材料中π相移畴壁分散马约拉纳态的观察结果一致。
Abstract
The possible realization of Majorana fermions as quasiparticle excitations in condensed-matter physics has created much excitement. Most studies have focused on Majorana bound states; however, propagating Majorana states with linear dispersion have also been predicted. Here, we report scanning scanning tunneling spectroscopic measurements of crystalline domain walls (DWs) in FeSe0.45Te0.55. We located DWs across which the lattice structure shifts by half a unit cell. These DWs have a finite, flat density of states inside the superconducting gap, which is a hallmark of linearly dispersing modes in one dimension. This signature is absent in DWs in the related superconductor, FeSe, which is not in the topological phase. Our combined data are consistent with the observation of dispersing Majorana states at a π-phase shift DW in a proximitized topological material.
A
single photonic cavity with two independent physical synthetic dimensions具有两个独立合成维度的单个光子腔
作者：Avik Dutt, Qian Lin, Luqi Yuan, Momchil Minkov, Meng Xiao, Shanhui Fan
链接：
https://science.sciencemag.org/content/367/6473/59
摘要：
因其为实现有效的规范势和拓扑物理学提供了一个多样的平台，合成维度的概念激发了从冷原子物理到光子学许多科学领域的兴趣。
以前的实验已经通过一个合成维度增强了现实空间维度。在这项研究中，我们将两个独立合成维度赋予单个环谐振器。
我们的系统由一个短时调制的环谐振器组成，该谐振器具有顺时针和逆时针模式之间的空间耦合，为光子在环形内传播创造了一个沿着频率和赝自旋自由度的合成霍尔梯子晶格。
我们观察到在合成维度上进行的多种物理现象，包括有效的自旋轨道耦合、磁场、自旋动量锁定以及拓扑单向边界流的特征。我们的实验证明，高维度物理效应可以通过利用多个同时合成维的概念进行研究。
Abstract
The concept of synthetic dimensions has generated interest in many branches of science, ranging from ultracold atomic physics to photonics, as it provides a versatile platform for realizing effective gauge potentials and topological physics. Previous experiments have augmented the real-space dimensionality by one additional physical synthetic dimension. In this study, we endow a single ring resonator with two independent physical synthetic dimensions. Our system consists of a temporally modulated ring resonator with spatial coupling between the clockwise and counterclockwise modes, creating a synthetic Hall ladder along the frequency and pseudospin degrees of freedom for photons propagating in the ring. We observe a wide variety of physics, including effective spin-orbit coupling, magnetic fields, spin-momentum locking, a Meissner-to-vortex phase transition, and signatures of topological chiral one-way edge currents, completely in synthetic dimensions. Our experiments demonstrate that higher-dimensional physics can be studied in simple systems by leveraging the concept of multiple simultaneous synthetic dimensions.
Topological mechanics of knots and tangles结和缠结的拓扑力学
作者：Vishal P. Patil, Joseph D. Sandt, Mathias Kolle, Jörn Dunkel
链接：
https://science.sciencemag.org/content/367/6473/71
摘要：
结在生物和物理系统动力学中扮演着重要的角色，从DNA到湍流等离子体，以及攀登、编织、航海和外科手术。
尽管已经过了几个世纪的研究，但人们对弹性结的拓扑结构和力学之间微妙的相互作用仍然知之甚少。
在此，我们结合光力学实验理论和模拟来分析打结纤维在机械变形下的颜色变化。利用一个长距离铁磁自旋系统类比，我们确定了简单的拓扑计数规则来预测结和缠结的相对机械稳定性，这与常用的攀登和航行弯道的模拟和实验相一致。
我们的结果突出了扭转和扭曲在打结过程中的重要性，并为复杂缠结系统的控制提供了指导。
Abstract
Knots play a fundamental role in the dynamics of biological and physical systems, from DNA to turbulent plasmas, as well as in climbing, weaving, sailing, and surgery. Despite having been studied for centuries, the subtle interplay between topology and mechanics in elastic knots remains poorly understood. Here, we combined optomechanical experiments with theory and simulations to analyze knotted fibers that change their color under mechanical deformations. Exploiting an analogy with long-range ferromagnetic spin systems, we identified simple topological counting rules to predict the relative mechanical stability of knots and tangles, in agreement with simulations and experiments for commonly used climbing and sailing bends. Our results highlight the importance of twist and writhe in unknotting processes, providing guidance for the control of systems with complex entanglements.
On-chip integrated laser-driven particle accelerator芯片上集成的激光驱动粒子加速器
作者：Neil V. Sapra, Ki Youl Yang, Dries Vercruysse, Kenneth J. Leedle, Dylan S. Black, R. Joel England, Logan Su, Rahul, et al
链接：
https://science.sciencemag.org/content/367/6473/79
摘要：
粒子加速器是科学和工业中必不可少的工具。然而，常规射频加速器的尺寸和成本限制了该技术的实用性和可用范围。
介质激光加速器（DLAs）通过使用可见或近红外脉冲激光驱动加速器纳米结构，提供了一种经济有效的解决方案，使尺寸缩小了104倍。目前介质激光加速器的实现依赖于自由空间激光直接入射到加速结构上，限制了这项技术的可扩展性和可积性。
我们提出了一个波导集成DLA的实验演示，该设计采用了光子反设计方法。通过比较测量的电子能谱和粒子跟踪模拟，我们推断在30微米以上的最大能量增益为0.915千电子伏特，对应于每米30.5兆电子伏特的加速度梯度。芯片加速器为完全集成的超大电子伏特级DLA提供了可能性。
Abstract
Particle accelerators represent an indispensable tool in science and industry. However, the size and cost of conventional radio-frequency accelerators limit the utility and reach of this technology. Dielectric laser accelerators (DLAs) provide a compact and cost-effective solution to this problem by driving accelerator nanostructures with visible or near-infrared pulsed lasers, resulting in a 104 reduction of scale. Current implementations of DLAs rely on free-space lasers directly incident on the accelerating structures, limiting the scalability and integrability of this technology. We present an experimental demonstration of a waveguide-integrated DLA that was designed using a photonic inverse-design approach. By comparing the measured electron energy spectra with particle-tracking simulations, we infer a maximum energy gain of 0.915 kilo–electron volts over 30 micrometers, corresponding to an acceleration gradient of 30.5 mega–electron volts per meter. On-chip acceleration provides the possibility for a completely integrated mega–electron volt-scale DLA.
材料科学
Materials Science
Oriented attachment induces fivefold twins by forming and decomposing high-energy grain boundaries定向附着通过形成和分解高能晶界产生五重孪晶
作者：Miao Song, Gang Zhou, Ning Lu, Jaewon Lee, Elias Nakouzi, Hao Wang, Dongsheng Li
链接：
https://science.sciencemag.org/content/367/6473/40
摘要：
天然和合成纳米粒子组成的五重孪晶畴具有独特的性质。但人们对五重孪晶纳米粒子的组成机制了解甚少。
我们使用原位高分辨透射电子显微镜结合分子动力学模拟来证明，通过重复定向连接~3纳米金、铂和钯纳米颗粒，可以产生五重孪晶。我们发现了两种不同的形成五重孪晶纳米粒子的机制，这些机制是由应变的积累和消除所驱动的。
伴随着晶界的分解，形成了一个特殊的、净应变为零的双晶系。这些观察使我们能够对双晶形成过程完成一个定量的描述。该机制为在广泛中控制大量材料的双晶结构和形态提供了指导。
Abstract
Natural and synthetic nanoparticles composed of fivefold twinned crystal domains have distinct properties. The formation mechanism of these fivefold twinned nanoparticles is poorly understood. We used in situ high-resolution transmission electron microscopy combined with molecular dynamics simulations to demonstrate that fivefold twinning occurs through repeated oriented attachment of ~3-nanometer gold, platinum, and palladium nanoparticles. We discovered two different mechanisms for forming fivefold twinned nanoparticles that are driven by the accumulation and elimination of strain. This was accompanied by decomposition of grain boundaries and the formation of a special class of twins with a net strain of zero. These observations allowed us to develop a quantitative picture of the twinning process. The mechanisms provide guidance for controlling twin structures and morphologies across a wide range of materials.
考古学Archaeology
Cooked starchy rhizomes in Africa 170 thousand years ago科学家在非洲发现17万年前的煮熟淀粉根状茎
作者：Lyn Wadley, Lucinda Backwell, Francesco d’Errico, Christine Sievers
链接：
https://science.sciencemag.org/content/367/6473/87
摘要：
毫无疑问，古人会食用植物碳水化合物，但淀粉类地下芽植物却很少能在考古学中被发现。
我们发现了至少17万年前的早期人类利用开发地下芽植物的证据。通过古代和现代根茎的形态和解剖学比较，我们认为，来自南非边境洞穴中的烧焦根状茎为Hypoxis L. 属。Hypoxis angustifolia Lam.（可能的分类群）大量生长在撒哈拉以南的非洲和阿拉伯也门相对水资源丰富的地区。
在那些地区以及更北的区域，Hypoxis的根茎可以为流动群体提供可靠和常见的碳水化合物来源。
Abstract
Plant carbohydrates were undoubtedly consumed in antiquity, yet starchy geophytes were seldom preserved archaeologically. We report evidence for geophyte exploitation by early humans from at least 170,000 years ago. Charred rhizomes from Border Cave, South Africa, were identified to the genus Hypoxis L. by comparing the morphology and anatomy of ancient and modern rhizomes. Hypoxis angustifolia Lam., the likely taxon, proliferates in relatively well-watered areas of sub-Saharan Africa and in Yemen, Arabia. In those areas and possibly farther north during moist periods, Hypoxis rhizomes would have provided reliable and familiar carbohydrate sources for mobile groups.
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