《自然》（20230413出版）一周论文导读
2023/4/15 20:15:19 科学网

     编译 | 未玖

     Nature, 13 April 2023, VOL 616, ISSUE 7956

     《自然》2023年4月13日，第616卷，7956期

    

     天文学Astronomy

     A population of red candidate massive galaxies ~600 Myr after the Big Bang

     大爆炸后约6亿年的红色候选大质量星系群

     ▲ 作者：Ivo Labbé, Pieter van Dokkum, Erica Nelson, Rachel Bezanson, Katherine A. Suess, Joel Leja, et al.

     ▲ 链接：

     https://www.nature.com/articles/s41586-023-05786-2

     ▲ 摘要：

     大爆炸约10亿年之后，恒星质量高达大约10¹¹太阳质量的星系已被确定红移z大约为6。但人们很难找到更早时候的大质量星系，因为精确估计质量所需的巴尔默断裂区域红移至波长超过2.5 μm。

     研究组利用詹姆斯·韦伯太空望远镜早期发布观测数据的1-5 μm覆盖范围来搜索宇宙历史最初大约7.5亿年的本征红色星系。在调查区域，研究组发现了7.4≤z≤9.1、大爆炸后5~7亿年的6个候选大质量星系(恒星质量超过10¹⁰太阳质量)，其中一个星系可能存在约10¹¹太阳质量的恒星。

     如果用光谱学验证，大质量星系中的恒星质量密度将远远高于先前基于静止帧紫外线选择样本的研究预期值。

     ▲ Abstract：

     Galaxies with stellar masses as high as roughly 10¹¹ solar masses have been identified out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. Here we make use of the 1–5 μm coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 10¹⁰ solar masses) at 7.4≤z≤ 9.1, 500–700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 10¹¹ solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples.

     物理学Physics

     Giant magnetoresistance of Dirac plasma in high-mobility graphene

     高迁移率石墨烯中狄拉克等离子体的巨磁阻

     ▲ 作者：Na Xin, James Lourembam, Piranavan Kumaravadivel, A. E. Kazantsev, Zefei Wu, Ciaran Mullan, et al.

     ▲ 链接：

     https://www.nature.com/articles/s41586-023-05807-0

     ▲ 摘要：

     石墨烯电子能谱最明显的特征是其狄拉克点，该点周围经常发生各种有趣的现象。在低温时，这种状态下的本征行为通常被电荷不均匀性所掩盖，但热激发可克服高温下的无序，并产生狄拉克费米子的电子-空穴等离子体。人们发现狄拉克等离子体具有不同寻常的特性，包括量子临界散射和流体动力学流动，但对等离子体在磁场中的行为知之甚少。

     研究组报道了这种量子临界状态下的磁输运。在低磁场中，等离子体在室温0.1特斯拉的磁场中表现出巨大的抛物线磁阻，达到100%以上。这比在该温度下任何其他系统中发现的磁阻高出几个数量级。

     研究组表明这种行为是单层石墨烯独有的，尽管经常发生(普朗克极限)散射，但仍表现出无质量光谱和超高迁移率。在几特斯拉的磁场中，随着朗道量子化的开始，电子-空穴等离子体完全位于第零朗道能级，出现了巨线性磁阻。

     巨磁阻几乎与温度无关，可通过近距离筛选来抑制，表明其是多体起源的。这与奇异金属中的磁输运和Weyl金属预测的所谓量子线性磁阻颇为相似，使用这个定义明确的量子临界二维系统有望进一步探索相关物理学。

     ▲ Abstract：

     The most recognizable feature of graphene’s electronic spectrum is its Dirac point, around which interesting phenomena tend to cluster. At low temperatures, the intrinsic behaviour in this regime is often obscured by charge inhomogeneity but thermal excitations can overcome the disorder at elevated temperatures and create an electron–hole plasma of Dirac fermions. The Dirac plasma has been found to exhibit unusual properties, including quantum-critical scattering and hydrodynamic flow. However, little is known about the plasma’s behaviour in magnetic fields. Here we report magnetotransport in this quantum-critical regime. In low fields, the plasma exhibits giant parabolic magnetoresistivity reaching more than 100?per cent in a magnetic field of 0.1 tesla at room temperature. This is orders-of-magnitude higher than magnetoresistivity found in any other system at such temperatures. We show that this behaviour is unique to monolayer graphene, being underpinned by its massless spectrum and ultrahigh mobility, despite frequent (Planckian limit) scattering. With the onset of Landau quantization in a magnetic field of a few tesla, where the electron–hole plasma resides entirely on the zeroth Landau level, giant linear magnetoresistivity emerges. It is nearly independent of temperature and can be suppressed by proximity screening, indicating a many-body origin. Clear parallels with magnetotransport in strange metals and so-called quantum linear magnetoresistance predicted for Weyl metals offer an interesting opportunity to further explore relevant physics using this well defined quantum-critical two-dimensional system.

     Orbital-resolved observation of singlet fission

     单线态裂变的轨道分辨观测

     ▲ 作者：Alexander Neef, Samuel Beaulieu, Sebastian Hammer, Shuo Dong, Julian Maklar, Tommaso Pincelli, et al.

     ▲ 链接：

     https://www.nature.com/articles/s41586-023-05814-1

     ▲ 摘要：

     单线态裂变可通过将一个单线态激子转化为两个三重态激子从而使激发电荷载流子数量翻倍来提高光伏效率。单线态裂变的主要步骤是相关三重态对的超快产生。虽然人们已提出若干机制来解释这一步骤，但尚未形成共识。主要挑战在于追踪瞬态激子态。

     研究组利用时间-角度分辨的光电发射光谱，观测了结晶并五苯中单线态裂变的主要步骤。该结果表明，在最低亮度的单线态激子中，电荷转移介导的机制伴随着Frenkel态和电荷转移态的杂化。

     研究组深入理解了动量图中记录的激子波函数的局域化和轨道特征，实现了单线态和双三重态激子局域化的直接比较，并根据其轨道特征分解能量重叠态。轨道和局域化解析的多体动力学有望深入了解控制分子系统和拓扑材料的力学。

     ▲ Abstract：

     Singlet fission may boost photovoltaic efficiency by transforming a singlet exciton into two triplet excitons and thereby doubling the number of excited charge carriers. The primary step of singlet fission is the ultrafast creation of the correlated triplet pair. Whereas several mechanisms have been proposed to explain this step, none has emerged as a consensus. The challenge lies in tracking the transient excitonic states. Here we use time- and angle-resolved photoemission spectroscopy to observe the primary step of singlet fission in crystalline pentacene. Our results indicate a charge-transfer mediated mechanism with a hybridization of Frenkel and charge-transfer states in the lowest bright singlet exciton. We gained intimate knowledge about the localization and the orbital character of the exciton wave functions recorded in momentum maps. This allowed us to directly compare the localization of singlet and bitriplet excitons and decompose energetically overlapping states on the basis of their orbital character. Orbital- and localization-resolved many-body dynamics promise deep insights into the mechanics governing molecular systems and topological materials.

     材料科学Materials Science

     Mechanistic formulation of inorganic membranes at the air–liquid interface

     气-液界面无机膜的机械形成

     ▲ 作者：Chen Zhang, Wanheng Lu, Yingfeng Xu, Kaiyang Zeng & Ghim Wei Ho

     ▲ 链接：

     https://www.nature.com/articles/s41586-023-05809-y

     ▲ 摘要：

     独立功能无机膜超越了有机和聚合物膜的极限，可以释放高级分离、催化、传感器、存储器、光学过滤和离子导体的潜力。然而，大多数无机材料的脆性，以及表面缺乏不饱和键，意味着很难通过传统的自上而下的成型和/或自下而上的合成形成连续的膜。到目前为止，只有少数几种特定的无机膜通过选择性去除牺牲底物由预沉积膜来制备。

     研究组展示了一种在无机前驱体的水体系中切换成核偏好的策略，导致在气-液界面形成各种超薄无机膜。力学研究表明，膜的生长依赖于漂浮构建块的运动演化，这有助于基于几何连通性推导出相图。

     这种见解为任何未开发的膜提供了通用合成指导，还提供了调整膜厚度和通孔参数的通用原则。除了理解复杂动态系统外，该研究还从组成、结构和功能等方面全面扩展了膜的传统概念。

     ▲ Abstract：

     Freestanding functional inorganic membranes, beyond the limits of their organic and polymeric counterparts, may unlock the potentials of advanced separation, catalysis, sensors, memories, optical filtering and ionic conductors. However, the brittle nature of most inorganic materials, and the lack of surface unsaturated linkages, mean that it is difficult to form continuous membranes through conventional top-down mouldings and/or bottom-up syntheses. Up to now, only a few specific inorganic membranes have been fabricated from predeposited films by selective removal of sacrificial substrates. Here we demonstrate a strategy to switch nucleation preferences in aqueous systems of inorganic precursors, resulting in the formation of various ultrathin inorganic membranes at the air–liquid interface. Mechanistic study shows that membrane growth depends on the kinematic evolution of floating building blocks, which helps to derive the phase diagram based on geometrical connectivity. This insight provides general synthetic guidance towards any unexplored membranes, as well as the principle of tuning membrane thickness and through-hole parameters. Beyond understanding a complex dynamic system, this study comprehensively expands the traditional notion of membranes in terms of composition, structure and functionality.

     化学Chemistry

     Dehydration of a crystal hydrate at subglacial temperatures

     晶体水合物在低于冰点温度下的脱水

     ▲ 作者：Alan C. Eaby, Dirkie C. Myburgh, Akmal Kosimov, Marcin Kwit, Catharine Esterhuysen, Agnieszka M. Janiak, et al.

     ▲ 链接：

     https://www.nature.com/articles/s41586-023-05749-7

     ▲ 摘要：

     水是地球上最重要的物质之一。它以固体、液体和蒸汽的状态普遍存在，所有已知的生物系统都依赖于其独特的化学和物理性质。此外，许多材料以水合物的形式存在，其中最主要的是晶体水合物(一种特殊的包合物)，其通常在低于环境温度下无限期地保留水分。

     研究组描述了一种多孔有机晶体，在相对湿度超过55%的情况下很容易且可逆地将水吸附到1纳米宽的通道中。水的吸收/释放是显色的，从而在宽温度范围内提供了一个晶体水合状态的便利视觉指示。利用X射线衍射、光学显微镜、差示扫描量热法和分子模拟等辅助技术来确定纳米限域水处于-70°C以上的通量状态，以实现低温脱水。

     研究组确定了在广泛温度范围内(包括远低于0℃，该温度下由于大气水分的存在，通常很难完成)的脱水动力学。该发现将助力设计能够在远低于体相水冰点的温度范围内捕获/释放水的材料。

     ▲ Abstract：

     Water is one of the most important substances on our planet. It is ubiquitous in its solid, liquid and vaporous states and all known biological systems depend on its unique chemical and physical properties. Moreover, many materials exist as water adducts, chief among which are crystal hydrates (a specific class of inclusion compound), which usually retain water indefinitely at subambient temperatures. We describe a porous organic crystal that readily and reversibly adsorbs water into 1-nm-wide channels at more than 55% relative humidity. The water uptake/release is chromogenic, thus providing a convenient visual indication of the hydration state of the crystal over a wide temperature range. The complementary techniques of X-ray diffraction, optical microscopy, differential scanning calorimetry and molecular simulations were used to establish that the nanoconfined water is in a state of flux above -70°C, thus allowing low-temperature dehydration to occur. We were able to determine the kinetics of dehydration over a wide temperature range, including well below 0°C which, owing to the presence of atmospheric moisture, is usually challenging to accomplish. This discovery unlocks opportunities for designing materials that capture/release water over a range of temperatures that extend well below the freezing point of bulk water.

     地球科学Earth Science

     Earth shaped by primordialH₂ atmospheres

     原始H₂大气形成了地球

     ▲ 作者：Edward D. Young, Anat Shahar & Hilke E. Schlichting

     ▲ 链接：

     https://www.nature.com/articles/s41586-023-05823-0

     ▲ 摘要：

     地球上的水、本征氧化态和金属核心密度是地球的基本化学特征。对系外行星的研究为阐明这些化学特征的来源提供了有用的背景。行星形成和演化模型表明，岩石系外行星通常由富氢包裹层形成，这些包裹层随着时间的推移而消失。这些发现表明，地球也可能由富氢原始大气形成。

     研究组使用一个自洽热力学模型来表明，地球的水、核心密度和整体氧化状态都可以源于富氢原始大气和其祖行星胚胎中底层岩浆海洋之间的平衡。由于岩浆海洋中的氧气与氢反应，水从类似顽火辉石球粒陨石的干燥初始物质产生。

     从大气中产生的氢进入岩浆海洋，最终进入处于平衡状态的金属核心，导致金属密度低于地球密度。硅酸盐岩石从类太阳氧逸度氧化为类地球氧逸度，随之而来的还有硅、氢和氧，以及内核中的铁合金。

     因此，与氢大气层的反应和金属-硅酸盐平衡为地球化学基本特征提供了一个简单的解释，这与整个银河系的岩石行星形成一致。

     ▲ Abstract：

     Earth’s water, intrinsic oxidation state and metal core density are fundamental chemical features of our planet. Studies of exoplanets provide a useful context for elucidating the source of these chemical traits. Planet formation and evolution models demonstrate that rocky exoplanets commonly formed with hydrogen-rich envelopes that were lost over time. These findings suggest that Earth may also have formed from bodies with hydrogen-rich primary atmospheres. Here we use a self-consistent thermodynamic model to show that Earth’s water, core density and overall oxidation state can all be sourced to equilibrium between hydrogen-rich primary atmospheres and underlying magma oceans in its progenitor planetary embryos. Water is produced from dry starting materials resembling enstatite chondrites as oxygen from magma oceans reacts with hydrogen. Hydrogen derived from the atmosphere enters the magma ocean and eventually the metal core at equilibrium, causing metal density deficits matching that of Earth. Oxidation of the silicate rocks from solar-like to Earth-like oxygen fugacities also ensues as silicon, along with hydrogen and oxygen, alloys with iron in the cores. Reaction with hydrogen atmospheres and metal–silicate equilibrium thus provides a simple explanation for fundamental features of Earth’s geochemistry that is consistent with rocky planet formation across the Galaxy.

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