编译 | 未玖

Nature, 19 October 2023, VOL 622, ISSUE 7983

《自然》2023年10月19日，第622卷，7983期

物理学Physics

Coherent nanophotonic electron accelerator

相干纳米光子电子加速器

▲ 作者：Tomáš Chlouba, Roy Shiloh, Stefanie Kraus, Leon Brückner, Julian Litzel & Peter Hommelhoff

▲ 链接：

https://www.nature.com/articles/s41586-023-06602-7

▲ 摘要：

粒子加速器是工业、科学和医学各个领域必不可少的重要工具。通常，这些机器的占地面积从医疗应用的几平方米开始，逐步达到大型研究中心的规模。借助光子纳米结构内部激光来加速电子代表了一种微观替代方案，其成本和尺寸有望降低几个数量级。

尽管人们在介电激光加速研究上付出了巨大努力，包括利用光学力调控复杂的电子相空间，但迄今为止尚未显示出有效能量增益。

研究组展示了一种可扩展的纳米光子电子加速器，其相干结合了粒子加速和横向束限制，并在仅225 nm宽的通道中加速和引导电子超过长达500 μm的距离。结果观察到12.3 keV的最大相干能量增益，相当于增加了43%，从最初的28.4 keV增加到40.7 keV。

研究组希冀，这项工作能直接促进纳米光子加速器的出现，利用最小尺寸要求的高损伤阈值介电材料，提供高达GeV/m级的高加速梯度。这些片上粒子加速器将在医学、工业、材料研究和科学领域实现变革性应用。

▲ Abstract：

Particle accelerators are essential tools in a variety of areas of industry, science and medicine. Typically, the footprint of these machines starts at a few square metres for medical applications and reaches the size of large research centres. Acceleration of electrons with the help of laser light inside of a photonic nanostructure represents a microscopic alternative with potentially orders-of-magnitude decrease in cost and size. Despite large efforts in research on dielectric laser acceleration, including complex electron phase space control with optical forces, noteworthy energy gains have not been shown so far. Here we demonstrate a scalable nanophotonic electron accelerator that coherently combines particle acceleration and transverse beam confinement, and accelerates and guides electrons over a considerable distance of 500 μm in a just 225-nm-wide channel. We observe a maximum coherent energy gain of 12.3 keV, equalling a substantial 43% energy increase of the initial 28.4 keV to 40.7 keV. We expect this work to lead directly to the advent of nanophotonic accelerators offering high acceleration gradients up to the GeV m-1 range utilizing high-damage-threshold dielectric materials at minimal size requirements. These on-chip particle accelerators will enable transformative applications in medicine, industry, materials research and science.

Cavity-mediated thermal control of metal-to-insulator transition in 1T-TaS2

1T-TaS2中金属-绝缘体转变的腔介导热调控

▲ 作者：Giacomo Jarc, Shahla Yasmin Mathengattil, Angela Montanaro, Francesca Giusti, Enrico Maria Rigoni, Rudi Sergo, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06596-2

▲ 摘要：

通过弱光和强光—物质耦合，将量子材料置入光学腔中为控制物质的量子协同特性提供了一个独特平台。

研究组报道了关联固态材料中金属到绝缘体相变的可逆腔控制的实验证据。将电荷密度波材料1T-TaS2嵌入到低温可调谐的太赫兹腔中，揭示了通过机械调节腔镜之间的距离及其排列，可获得与样品温度较大变化相关的导电—绝缘行为之间的切换。

观察到的较大热变化表明了类似珀塞尔效应的情况，其中腔的光谱轮廓改变了材料与外部电磁场之间的能量交换。该发现将助力通过设计量子材料的电磁环境来控制其热力学和宏观输运特性。

▲ Abstract：

Placing quantum materials into optical cavities provides a unique platform for controlling quantum cooperative properties of matter, by both weak and strong light–matter coupling. Here we report experimental evidence of reversible cavity control of a metal-to-insulator phase transition in a correlated solid-state material. We embed the charge density wave material 1T-TaS2 into cryogenic tunable terahertz cavities and show that a switch between conductive and insulating behaviours, associated with a large change in the sample temperature, is obtained by mechanically tuning the distance between the cavity mirrors and their alignment. The large thermal modification observed is indicative of a Purcell-like scenario in which the spectral profile of the cavity modifies the energy exchange between the material and the external electromagnetic field. Our findings provide opportunities for controlling the thermodynamics and macroscopic transport properties of quantum materials by engineering their electromagnetic environment.

材料科学Materials Science

Tautomeric mixture coordination enables efficient lead-free perovskite LEDs

互变异构混合物配位实现高效无铅钙钛矿LED

▲ 作者：Dongyuan Han, Jie Wang, Lorenzo Agosta, Ziang Zang, Bin Zhao, Lingmei Kong, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06514-6

▲ 摘要：

卤化铅钙钛矿发光二极管（PeLEDs）具备优异的光电性能。然而，铅存在潜在毒性问题，在不影响其高外部量子效率的情况下，从性能最好的PeLEDs中去除铅仍颇具挑战。

研究组报道了一种通过引入氰尿酸来稳定无铅锡钙钛矿TEA2SnI4（TEAI，2—噻吩乙基碘化铵）的互变异构体—混合物—配位诱导的电子局域策略。结果证明配位的一个关键功能是放大电子效应，即使对于那些因在钙钛矿表面形成氢键互变异构二聚体和三聚体超结构而与氰尿酸不能形成强键的锡原子亦是如此。

这种电子局域化弱化了安德森局域化的不利影响，提高了TEA2SnI4晶体结构的有序性。这些因素导致非辐射复合捕获系数降低了两个数量级，同时激子结合能提高了约两倍。该无铅PeLEDs具有高达20.29%的外部量子效率，其性能可与最先进的含铅PeLEDs相媲美。

研究组希冀，这些发现将为Sn（II）钙钛矿的稳定性提供见解，并进一步推动无铅钙钛矿的应用。

▲ Abstract：

Lead halide perovskite light-emitting diodes (PeLEDs) have demonstrated remarkable optoelectronic performance. However, there are potential toxicity issues with lead and removing lead from the best-performing PeLEDs—without compromising their high external quantum efficiencies—remains a challenge. Here we report a tautomeric-mixture-coordination-induced electron localization strategy to stabilize the lead-free tin perovskite TEA2SnI4 (TEAI is 2-thiopheneethylammonium iodide) by incorporating cyanuric acid. We demonstrate that a crucial function of the coordination is to amplify the electronic effects, even for those Sn atoms that aren’t strongly bonded with cyanuric acid owing to the formation of hydrogen-bonded tautomeric dimer and trimer superstructures on the perovskite surface. This electron localization weakens adverse effects from Anderson localization and improves ordering in the crystal structure of TEA2SnI4. These factors result in a two-orders-of-magnitude reduction in the non-radiative recombination capture coefficient and an approximately twofold enhancement in the exciton binding energy. Our lead-free PeLED has an external quantum efficiency of up to 20.29%, representing a performance comparable to that of state-of-the-art lead-containing PeLEDs. We anticipate that these findings will provide insights into the stabilization of Sn(II) perovskites and further the development of lead-free perovskite applications.

Flatband λ-Ti3O5 towards extraordinary solar steam generation

平带λ-Ti3O5助力高效太阳能蒸汽生成

▲ 作者：Bo Yang, Zhiming Zhang, Peitao Liu, Xiankai Fu, Jiantao Wang, Yu Cao, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06509-3

▲ 摘要：

太阳能蒸汽界面蒸发因其环境友好的特点，在海水淡化和污水净化方面具有广阔的应用前景。为了提高太阳能蒸汽生成的效率，先前的大部分努力都集中在有效地收集全太阳光谱的太阳能上。然而，调节联合态密度对增强光热材料太阳能吸收的重要性却未得到重视。

研究组提出了一种通过引入平带电子结构来大大提高联合态密度的策略。结果表明，由于Ti-Ti二聚体在费米能级附近诱导的平带，金属λ-Ti3O5粉末具有96.4%的高太阳能吸收率。通过将λ-Ti3O5粉末纳入具有锥形腔的三维多孔水凝胶蒸发器中，在一倍太阳光照且没有盐沉淀的情况下，对3.5 wt%的盐水实现了前所未有的高蒸发率，约为6.09 kg/m2/h。

从根本上而言，暴露在λ-Ti3O5表面的Ti-Ti二聚体和U型槽结构有利于吸附水分子的解离，并有利于界面水以小分子团簇的形式蒸发。当前工作强调了Ti-Ti二聚体诱导的平带在增强太阳能吸收以及特殊U型槽在促进水解离中的关键作用，这为获得具有成本效益的太阳能—蒸汽生成提供了见解。

▲ Abstract：

Solar steam interfacial evaporation represents a promising strategy for seawater desalination and wastewater purification owing to its environmentally friendly character. To improve the solar-to-steam generation, most previous efforts have focused on effectively harvesting solar energy over the full solar spectrum. However, the importance of tuning joint densities of states in enhancing solar absorption of photothermal materials is less emphasized. Here we propose a route to greatly elevate joint densities of states by introducing a flat-band electronic structure. Our study reveals that metallic λ-Ti3O5 powders show a high solar absorptivity of 96.4% due to Ti–Ti dimer-induced flat bands around the Fermi level. By incorporating them into three-dimensional porous hydrogel-based evaporators with a conical cavity, an unprecedentedly high evaporation rate of roughly 6.09 kilograms per square metre per hour is achieved for 3.5 weight percent saline water under 1 sun of irradiation without salt precipitation. Fundamentally, the Ti–Ti dimers and U-shaped groove structure exposed on the λ-Ti3O5 surface facilitate the dissociation of adsorbed water molecules and benefit the interfacial water evaporation in the form of small clusters. The present work highlights the crucial roles of Ti–Ti dimer-induced flat bands in enchaining solar absorption and peculiar U-shaped grooves in promoting water dissociation, offering insights into access to cost-effective solar-to-steam generation.

地球科学Earth Science

Overshooting the critical threshold for the Greenland ice sheet

格陵兰冰盖融化超过临界阈值

▲ 作者：Nils Bochow, Anna Poltronieri, Alexander Robinson, Marisa Montoya, Martin Rypdal & Niklas Boers

▲ 链接：

https://www.nature.com/articles/s41586-023-06503-9

▲ 摘要：

人为全球变暖导致格陵兰冰盖（GrIS）融化，对全球海平面上升（SLR）构成严重威胁。模型和古气候证据表明，北极迅速升高的温度可触发GrIS的正反馈机制，导致自身持续融化，GrIS已被证明可保持几种稳定状态。当全球平均温度（GMT）超过特定阈值时，预计会发生临界转变，在稳定状态之间存在显著滞后。

研究组使用两个独立的冰盖模型来研究具有不同峰值温度和收敛温度的不同超调情景对大范围变暖和随后变冷速率的影响。结果表明，最大GMT和超过给定GMT目标的时间跨度是决定GrIS稳定性的关键。

当阈值GMT比工业化前水平高出1.7℃至2.3℃时，或导致冰盖急剧消失。如果GMT随后在几个世纪内降低到比工业化前水平高1.5℃以下，即使最高GMT比工业化前水平高6℃及以上，GrIS的损失也可以大大减轻。

但研究结果也表明，即使暂时超过温度阈值，尚未过渡到新冰盖状态时，SLR仍会达到几米的峰值。

▲ Abstract：

Melting of the Greenland ice sheet (GrIS) in response to anthropogenic global warming poses a severe threat in terms of global sea-level rise (SLR). Modelling and palaeoclimate evidence suggest that rapidly increasing temperatures in the Arctic can trigger positive feedback mechanisms for the GrIS, leading to self-sustained melting, and the GrIS has been shown to permit several stable states. Critical transitions are expected when the global mean temperature (GMT) crosses specific thresholds, with substantial hysteresis between the stable states. Here we use two independent ice-sheet models to investigate the impact of different overshoot scenarios with varying peak and convergence temperatures for a broad range of warming and subsequent cooling rates. Our results show that the maximum GMT and the time span of overshooting given GMT targets are critical in determining GrIS stability. We find a threshold GMT between 1.7 ℃ and 2.3 ℃ above preindustrial levels for an abrupt ice-sheet loss. GrIS loss can be substantially mitigated, even for maximum GMTs of 6 ℃ or more above preindustrial levels, if the GMT is subsequently reduced to less than 1.5 ℃ above preindustrial levels within a few centuries. However, our results also show that even temporarily overshooting the temperature threshold, without a transition to a new ice-sheet state, still leads to a peak in SLR of up to several metres.

Tropical Atlantic multidecadal variability is dominated by external forcing

热带大西洋多年代际变化主要由外部强迫主导

▲ 作者：Chengfei He, Amy C. Clement, Sydney M. Kramer, Mark A. Cane, Jeremy M. Klavans, Tyler M. Fenske, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06489-4

▲ 摘要：

热带大西洋气候的特征表现为大西洋海表温度（SSTs）、萨赫勒降雨量和飓风活动显著且相关的多年代际变化。由于模型和观测的不确定性，这些系统之间物理关系的起源仍存在争议。

研究组表明，自1950年以来，热带大西洋SST的跨赤道梯度主要由与人为排放和火山气溶胶相关的辐射扰动驱动，这是大西洋飓风形成和萨赫勒降雨量的关键决定因素。这种关系在大量CMIP6地球系统模型中很模糊，因为这些模型高估了1950年左右以来北半球相对于南半球的长期变暖趋势，以及大气环流和降雨量的相关变化。

当消除高估趋势后，SST与大西洋飓风形成和萨赫勒降雨量之间的相关性表现出对辐射强迫的响应，特别是自1950年以来，当时人为气溶胶强迫一直很高。研究结果表明，热带大西洋SST梯度与整个北大西洋的SST相比，更能决定热带影响，因为该梯度通过局部大气环流与热带影响的物理联系更紧密。

该结果强调，大西洋飓风活动和萨赫勒降雨量变化可以通过人为排放和火山活动驱动的辐射强迫来预测，但更可靠的预测受到未来气候强迫的信噪比悖论和不确定性的限制。

▲ Abstract：

The tropical Atlantic climate is characterized by prominent and correlated multidecadal variability in Atlantic sea surface temperatures (SSTs), Sahel rainfall and hurricane activity. Owing to uncertainties in both the models and the observations, the origin of the physical relationships among these systems has remained controversial. Here we show that the cross-equatorial gradient in tropical Atlantic SSTs—largely driven by radiative perturbations associated with anthropogenic emissions and volcanic aerosols since 1950—is a key determinant of Atlantic hurricane formation and Sahel rainfall. The relationship is obscured in a large ensemble of CMIP6 Earth system models, because the models overestimate long-term trends for warming in the Northern Hemisphere relative to the Southern Hemisphere from around 1950 as well as associated changes in atmospheric circulation and rainfall. When the overestimated trends are removed, correlations between SSTs and Atlantic hurricane formation and Sahel rainfall emerge as a response to radiative forcing, especially since 1950 when anthropogenic aerosol forcing has been high. Our findings establish that the tropical Atlantic SST gradient is a stronger determinant of tropical impacts than SSTs across the entire North Atlantic, because the gradient is more physically connected to tropical impacts via local atmospheric circulations. Our findings highlight that Atlantic hurricane activity and Sahel rainfall variations can be predicted from radiative forcing driven by anthropogenic emissions and volcanism, but firmer predictions are limited by the signal-to-noise paradox and uncertainty in future climate forcings.