作者:未玖 来源:科学网微信公众号 发布时间:2023/12/2 20:25:47
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《自然》(20231130出版)一周论文导读

 

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Nature, 30 November 2023, VOL 623, ISSUE 7989

《自然》2023年11月30日,第623卷,7989期

物理学Physics

Imaging inter-valley coherent order in magic-angle twisted trilayer graphene

魔角扭曲三层石墨烯中的谷间相干序成像

▲ 作者:Hyunjin Kim, Youngjoon Choi, étienne Lantagne-Hurtubise, Cyprian Lewandowski, Alex Thomson, Lingyuan Kong, et al.

▲ 链接:

https://www.nature.com/articles/s41586-023-06663-8

▲ 摘要:

魔角扭曲三层石墨烯(MATTG)表现出一系列自发打破潜在对称性的强相关电子相。研究组使用扫描隧道显微镜研究了MATTG的相关相位,并确定了相互作用驱动的空间对称性破缺的显著特征。

低应变样品中,在每个莫尔晶胞大约两到三个电子或空穴的填充范围内,研究观察到石墨烯晶格的原子级重建,并伴随着隧穿光谱中的相关能隙。这种短尺度的重组表现为一个凯库勒超晶胞(意味着电子之间自发的谷间相干性),并在与能隙发展相一致的宽磁场和温度范围内持续存在。

覆盖多个莫尔晶胞的大比例尺图进一步揭示了凯库勒模式的缓慢演变,表明原子尺度重建与更长莫尔尺度上的平移对称性破缺共存。研究组使用自相关和傅立叶分析来提取这些相位的本征周期性,发现其与理论上不相称的凯库勒螺旋阶一致。

此外还发现,表征莫尔尺度调制的波长随着空穴掺杂远离带的半填充而单调减小,且对磁场的依赖性较弱。该研究结果为存在应变情况下MATTG相关相的性质提供了重要见解,并表明超导性可从谷间相干母态中出现。

▲ Abstract:

Magic-angle twisted trilayer graphene (MATTG) exhibits a range of strongly correlated electronic phases that spontaneously break its underlying symmetries. Here we investigate the correlated phases of MATTG using scanning tunnelling microscopy and identify marked signatures of interaction-driven spatial symmetry breaking. In low-strain samples, over a filling range of about two to three electrons or holes per moiré unit cell, we observe atomic-scale reconstruction of the graphene lattice that accompanies a correlated gap in the tunnelling spectrum. This short-scale restructuring appears as a Kekulé supercell—implying spontaneous inter-valley coherence between electrons—and persists in a wide range of magnetic fields and temperatures that coincide with the development of the gap. Large-scale maps covering several moiré unit cells further reveal a slow evolution of the Kekulé pattern, indicating that atomic-scale reconstruction coexists with translation symmetry breaking at a much longer moiré scale. We use auto-correlation and Fourier analyses to extract the intrinsic periodicity of these phases and find that they are consistent with the theoretically proposed incommensurate Kekulé spiral order. Moreover, we find that the wavelength characterizing moiré-scale modulations monotonically decreases with hole doping away from half-filling of the bands and depends weakly on the magnetic field. Our results provide essential insights into the nature of the correlated phases of MATTG in the presence of strain and indicate that superconductivity can emerge from an inter-valley coherent parent state.

材料科学Materials Science

A stable atmospheric-pressure plasma for extreme-temperature synthesis

用于极端温度合成的稳定大气压等离子体

▲ 作者:Hua Xie, Ning Liu, Qian Zhang, Hongtao Zhong, Liqun Guo, Xinpeng Zhao, et al.

▲ 链接:

https://www.nature.com/articles/s41586-023-06694-1

▲ 摘要:

等离子体能够产生超高温反应环境,可用于各种材料的合成和加工。然而,等离子体的体积有限、不稳定性和不均匀性使得大规模生产大块高温材料颇具挑战性。

研究组提出了一种由一对碳纤维尖端增强电极组成的等离子体装置,能够在大气压下使用垂直取向的长、短碳纤维组合产生均匀、超高温和稳定的等离子体(高达8000 K)。长碳纤维通过微火花放电在低击穿电压下引发等离子体,而短碳纤维将放电凝聚成体积大且稳定的超高温等离子体。

作为概念验证,研究组使用该工艺在几秒钟内合成了各种极端材料,包括超高温陶瓷(例如碳氮化铪)和难熔金属合金。此外,碳毡电极柔韧性很高,可塑造为各种合成造型。这种简单实用的等离子体技术或有助于克服高温合成中的挑战,并实现由可再生电力驱动的大规模电气化等离子体制造。

▲ Abstract:

Plasmas can generate ultra-high-temperature reactive environments that can be used for the synthesis and processing of a wide range of materials. However, the limited volume, instability and non-uniformity of plasmas have made it challenging to scalably manufacture bulk, high-temperature materials. Here we present a plasma set-up consisting of a pair of carbon-fibre-tip-enhanced electrodes that enable the generation of a uniform, ultra-high temperature and stable plasma (up to 8,000 K) at atmospheric pressure using a combination of vertically oriented long and short carbon fibres. The long carbon fibres initiate the plasma by micro-spark discharge at a low breakdown voltage, whereas the short carbon fibres coalesce the discharge into a volumetric and stable ultra-high-temperature plasma. As a proof of concept, we used this process to synthesize various extreme materials in seconds, including ultra-high-temperature ceramics (for example, hafnium carbonitride) and refractory metal alloys. Moreover, the carbon-fibre electrodes are highly flexible and can be shaped for various syntheses. This simple and practical plasma technology may help overcome the challenges in high-temperature synthesis and enable large-scale electrified plasma manufacturing powered by renewable electricity.

化学Chemistry

Associative pyridinium electrolytes for air-tolerant redox flow batteries

缔合吡啶鎓电解质助力耐空气氧化还原液流电池

▲ 作者:Mark E. Carrington, Kamil Soko?owski, Erlendur Jónsson, Evan Wenbo Zhao, Anton M. Graf, Israel Temprano, et al.

▲ 链接:

https://www.nature.com/articles/s41586-023-06664-7

▲ 摘要:

吡啶鎓电解质是基于液流电池储能颇有潜力的候选材料。然而,人们对其充放电过程和整体循环稳定性的潜在机制知之甚少。

研究组探讨了吡啶鎓电解质在代表性液流电池条件下的氧化还原行为,揭示了包含这些电解质电池的空气耐受性,同时提供了其可逆性的通用物理化学描述符。利用扩展双吡啶化合物的合成库跟踪吡啶鎓电解质在广泛电位范围内的性能,并将单线态—三线态自由能隙确定为成功预测先前未确定的容量衰减机制开始的描述符。

利用耦合原位核磁共振和电子顺磁共振波谱,研究组解释了这些电解质的氧化还原行为,并确定了存在电化学性能的两种不同机制(窄能隙和宽能隙)。在这两种机制中,他们将容量衰减与自由基物种的形成联系起来,进一步表明π—二聚化在抑制自由基与微量杂质(如溶解氧)之间的反应性方面起决定性作用。

该研究结果与围绕π—二聚体在氧化还原液流电池中作用的主流观点形成了直接对比,且能够有效地减轻氧气导致的容量衰减,即使在长时间(数天)暴露于空气中亦是如此。这些见解为新型电解质系统设计奠定了基础,该系统中还原物种的反应性由其对分子内和分子间自由基配对的倾向控制,从而能够在空气中运行。

▲ Abstract:

Pyridinium electrolytes are promising candidates for flow-battery-based energy storage. However, the mechanisms underlying both their charge–discharge processes and overall cycling stability remain poorly understood. Here we probe the redox behaviour of pyridinium electrolytes under representative flow battery conditions, offering insights into air tolerance of batteries containing these electrolytes while providing a universal physico-chemical descriptor of their reversibility. Leveraging a synthetic library of extended bispyridinium compounds, we track their performance over a wide range of potentials and identify the singlet–triplet free energy gap as a descriptor that successfully predicts the onset of previously unidentified capacity fade mechanisms. Using coupled operando nuclear magnetic resonance and electron paramagnetic resonance spectroscopies, we explain the redox behaviour of these electrolytes and determine the presence of two distinct regimes (narrow and wide energy gaps) of electrochemical performance. In both regimes, we tie capacity fade to the formation of free radical species, and further show that π-dimerization plays a decisive role in suppressing reactivity between these radicals and trace impurities such as dissolved oxygen. Our findings stand in direct contrast to prevailing views surrounding the role of π-dimers in redox flow batteries and enable us to efficiently mitigate capacity fade from oxygen even on prolonged (days) exposure to air. These insights pave the way to new electrolyte systems, in which reactivity of reduced species is controlled by their propensity for intra- and intermolecular pairing of free radicals, enabling operation in air.

On-surface synthesis of a doubly anti-aromatic carbon allotrope

双反芳香性碳同素异形体的表面合成

▲ 作者:Yueze Gao, Florian Albrecht, Igor Ron?evi?, Isaac Ettedgui, Paramveer Kumar, Lorel M. Scriven, et al.

▲ 链接:

https://www.nature.com/articles/s41586-023-06566-8

▲ 摘要:

合成碳同素异形体(如石墨烯、碳纳米管和富勒烯)已彻底改变了材料科学,并带来了新技术。人们已讨论了许多假设的碳同素异形体,但很少有实验研究。最近,动态共价化学和表面合成等非常规合成策略已被用于创造新形式碳,包括γ—石墨炔、富勒烯聚合物、联苯烯网络和环碳。

环[N]碳是由N个碳原子组成的分子环;迄今为止已报道的三种(N = 10、14和18)都是双芳香的,这就引发了一个问题:是否有可能制备双反芳香的版本?研究组报道了一种通过尖端诱导的表面化学来合成和表征反芳香碳同素异形体环[16]碳的策略。

除了原子力显微镜的结构信息外,他们还通过扫描隧道显微镜记录轨道密度图来探测其电子结构。环[16]碳的键长交替观察证实了其双反芳香性,与理论一致。C16的简单结构使其成为研究芳香性极限的有趣模型系统,其高反应性使其成为新型碳同素异形体颇有前景的前体。

▲ Abstract:

Synthetic carbon allotropes such as graphene, carbon nanotubes and fullerenes have revolutionized materials science and led to new technologies. Many hypothetical carbon allotropes have been discussed, but few have been studied experimentally. Recently, unconventional synthetic strategies such as dynamic covalent chemistry and on-surface synthesis have been used to create new forms of carbon, including γ-graphyne, fullerene polymers, biphenylene networks and cyclocarbons. Cyclo[N]carbons are molecular rings consisting of N carbon atoms; the three that have been reported to date (N = 10, 14 and 18) are doubly aromatic, which prompts the question: is it possible to prepare doubly anti-aromatic versions? Here we report the synthesis and characterization of an anti-aromatic carbon allotrope, cyclo[16]carbon, by using tip-induced on-surface chemistry. In addition to structural information from atomic force microscopy, we probed its electronic structure by recording orbital density maps with scanning tunnelling microscopy. The observation of bond-length alternation in cyclo[16]carbon confirms its double anti-aromaticity, in concordance with theory. The simple structure of C16 renders it an interesting model system for studying the limits of aromaticity, and its high reactivity makes it a promising precursor to novel carbon allotropes.

信息科学Information Science

Remote collaboration fuses fewer breakthrough ideas

远程协作融合更难产生突破性想法

▲ 作者:Yiling Lin, Carl Benedikt Frey & Lingfei Wu

▲ 链接:

https://www.nature.com/articles/s41586-023-06767-1

▲ 摘要:

创新理论强调社会网络和团队作为突破性发现推动者的作用。今天,世界各地的科学家和发明家比以往任何时候都数量更多且相互联系。然而,尽管越来越多的人有所发现,越来越多的想法能以新方式重新配置,但研究表明,新想法越来越难找到——这与重组增长理论相矛盾。

研究组解开了这个明显的谜题。他们分析了过去半个世纪全球2000万篇研究论文和400万份专利申请,率先记录了城市间远程协作的兴起,强调了全球科学家和发明家之间日益增长的相互联系。结果进一步表明,在所有领域、时期和团队规模中,这些远程团队的研究人员与他们的现场同行相比,始终不太可能取得突破性发现。

通过创建一个数据集来探索团队内部和跨空间知识生产中的劳动分工,结果发现,在分布式团队成员中,协作集中在涉及更多编码知识的后期技术任务上。然而,当知识是隐性的时候,他们不太可能在概念性任务上联合起来,比如构思新想法和设计研究。

研究组得出结论,尽管近年来数字技术取得了惊人的进步,但远程团队不太可能整合其成员的知识来产生新的、颠覆性的想法。

▲ Abstract:

Theories of innovation emphasize the role of social networks and teams as facilitators of breakthrough discoveries. Around the world, scientists and inventors are more plentiful and interconnected today than ever before. However, although there are more people making discoveries, and more ideas that can be reconfigured in new ways, research suggests that new ideas are getting harder to find—contradicting recombinant growth theory. Here we shed light on this apparent puzzle. Analysing 20 million research articles and 4 million patent applications from across the globe over the past half-century, we begin by documenting the rise of remote collaboration across cities, underlining the growing interconnectedness of scientists and inventors globally. We further show that across all fields, periods and team sizes, researchers in these remote teams are consistently less likely to make breakthrough discoveries relative to their on-site counterparts. Creating a dataset that allows us to explore the division of labour in knowledge production within teams and across space, we find that among distributed team members, collaboration centres on late-stage, technical tasks involving more codified knowledge. Yet they are less likely to join forces in conceptual tasks—such as conceiving new ideas and designing research—when knowledge is tacit. We conclude that despite striking improvements in digital technology in recent years, remote teams are less likely to integrate the knowledge of their members to produce new, disruptive ideas.

地球科学Earth Science

Ending extreme poverty has a negligible impact on global greenhouse gas emissions

消除极端贫困对全球温室气体排放的影响微乎其微

▲ 作者:Philip Wollburg, Stephane Hallegatte & Daniel Gerszon Mahler

▲ 链接:

https://www.nature.com/articles/s41586-023-06679-0

▲ 摘要:

不断增长的消费既是结束极端贫困的必要条件,也是温室气体排放的主要驱动因素之一,这在脱贫和限制全球变暖之间造成了潜在的紧张关系。从历史上看,大多数脱贫都因经济增长而发生,这意味着脱贫不仅需要增加贫困人口的消费,还需要增加高收入人群的消费。

研究组使用每天2.15美元的国际贫困线来估算缓解极端贫困所需的经济增长相关排放量。即使考虑到历史上的能源强度和碳强度模式,与缓解极端贫困相关的全球排放量增长也不大,每年为23.7亿吨二氧化碳当量,相当于2019年全球排放量的4.9%。

减少不平等、提高能源效率和能源脱碳可进一步缓解这种紧张关系:假设按照史上最好表现,2050年用于脱贫的排放量将减少90%。更雄心勃勃的贫困线要求更多国家实现更大的经济增长,这将导致明显更高的排放量。

研究结果表明,使世界发展目标和气候目标保持一致的挑战不在于调和极端脱贫与气候目标,而在于提供可持续的中等收入生活水平。

▲ Abstract:

Growing consumption is both necessary to end extreme poverty and one of the main drivers of greenhouse gas emissions, creating a potential tension between alleviating poverty and limiting global warming. Most poverty reduction has historically occurred because of economic growth, which means that reducing poverty entails increasing not only the consumption of people living in poverty but also the consumption of people with a higher income. Here we estimate the emissions associated with the economic growth needed to alleviate extreme poverty using the international poverty line of US $2.15 per day. Even with historical energy- and carbon-intensity patterns, the global emissions increase associated with alleviating extreme poverty is modest, at 2.37 gigatonnes of carbon dioxide equivalent per year or 4.9% of 2019 global emissions. Lower inequality, higher energy efficiency and decarbonization of energy can ease this tension further: assuming the best historical performance, the emissions for poverty alleviation in 2050 will be reduced by 90%. More ambitious poverty lines require more economic growth in more countries, which leads to notably higher emissions. The challenge to align the development and climate objectives of the world is not in reconciling extreme poverty alleviation with climate objectives but in providing sustainable middle-income standards of living.

 
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