《自然》（20201001出版）一周論文導讀​

翻譯 | 李言

nature, 1 October 2020, Volume 586 Issue 7827

《自然》2020年10月1日，第586卷，7827期

材料科學Material Science

Fractional antiferromagnetic skyrmion lattice induced by anisotropic couplings

各向異性偶合誘導的少數反鐵磁斯格明子

▲ 作者：Shang Gao, H. Diego Rosales, Flavia A. Gómez Albarracín, Vladimir Tsurkan, Guratinder Kaur, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2716-8

▲ 摘要

磁性斯格明子是具有納米級繞組自旋紋理的拓撲孤子，在自旋電子學應用有廣闊前景。

到目前為止，在各種磁體中都觀察到了斯格明子，這些磁體表現出與相鄰自旋近似平行的排列，但理論上具有反平行的相鄰自旋的斯格明子也有可能存在。這種反鐵磁斯格明子可能比傳統的鐵磁斯格明子允許更靈活的控制。

在此，通過結合中子散射測量和蒙特卡洛模擬，我們表明MnSc2S4中分數反鐵磁斯格明子是穩定的。我們所觀察到的晶格由三個反鐵磁耦合的子晶格組成，每個子晶格都是一個三角形的斯格明子晶格，它被分割成具有初始瓜（半Skyrmion）特徵的兩部分。

我們的工作表明，理論上提出的反鐵磁斯格明子可以穩定在真實材料中，這是邁向實現自旋電子器件的重要一步。

▲ Abstract

Magnetic skyrmions are topological solitons with a nanoscale winding spin texture that hold promise for spintronics applications. Skyrmions have so far been observed in a variety of magnets that exhibit nearly parallel alignment for neighbouring spins, but theoretically skyrmions with anti-parallel neighbouring spins are also possible. Such antiferromagnetic skyrmions may allow more flexible control than conventional ferromagnetic skyrmions. Here, by combining neutron scattering measurements and Monte Carlo simulations, we show that a fractional antiferromagnetic skyrmion lattice is stabilized in MnSc2S4 through anisotropic couplings. The observed lattice is composed of three antiferromagnetically coupled sublattices, and each sublattice is a triangular skyrmion lattice that is fractionalized into two parts with an incipient meron (half-skyrmion) character. Our work demonstrates that the theoretically proposed antiferromagnetic skyrmions can be stabilized in real materials and represents an important step towards their implementation in spintronic devices.

物理學Physics

Graphene-based Josephson junction microwave bolometer

基於石墨烯的約瑟夫森結微波輻射熱計

▲ 作者：Gil-Ho Lee, Dmitri K. Efetov, Woochan Jung, Leonardo Ranzani, Evan D. Walsh, Thomas A. Ohki, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2752-4

▲ 摘要

靈敏微波探測器在射電天文學、暗物質軸子搜索和超導量子信息科學中起著至關重要的作用。

為了利用石墨烯微小的電子比熱和導熱性，我們開發了一種嵌入在7.9千兆赫的微波諧振器中的超導-石墨烯-超導體約瑟夫森結測輻射熱計，其耦合效率超過99%。

依賴的約瑟夫遜合閘電流操作溫度、電荷密度、輸入功率和頻率的噪聲等效功率為7×10−19瓦特/平方根赫茲、對應一個32 GHz光子能量的解析度，達到在0.19 K時本徵熱波動的基本極限。

我們的研究結果表明，二維材料可以使測輻射熱計具有熱力學定律允許的最高靈敏度。

▲ Abstract

Sensitive microwave detectors are essential in radioastronomy, dark-matter axion searches and superconducting quantum information science. To utilize the minute electronic specific heat and thermal conductivity of graphene, we develop a superconductor–graphene–superconductor Josephson junction bolometer embedded in a microwave resonator with a resonance frequency of 7.9 gigahertz and over 99 per cent coupling efficiency. The dependence of the Josephson switching current on the operating temperature, charge density, input power and frequency shows a noise-equivalent power of 7×10−19 watts per square-root hertz, which corresponds to an energy resolution of a single 32-gigahertz photon, reaching the fundamental limit imposed by intrinsic thermal fluctuations at 0.19 kelvin. Our results establish that two-dimensional materials could enable the development of bolometers with the highest sensitivity allowed by the laws of thermodynamics.

Bolometer operating at the threshold for circuit quantum electrodynamics

測輻射熱計在電路量子電動力學的閾值下運行

▲ 作者：R. Kokkoniemi, J.-P. Girard, D. Hazra, A. Laitinen, J. Govenius, R. E. Lake, I. Sallinen, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2753-3

▲ 摘要

儘管速度和噪音水平的熱傳感器有巨大進步，此前沒有測輻射熱計遇到電路量子電動力學的閾值——時間常數為數百納秒，同時能量解析度的10 h兆赫（h是普朗克常數）。

在此，我們通過實驗演示了一個測輻射熱計，它在這個閾值下工作，噪聲當量功率為30 zeptowatts每平方根赫茲，與目前報導的最低值相當，在熱時間常數縮短兩個數量級，為500納秒。

這兩個值在同一裝置上直接測量，給出了一個精確的估計30h千兆赫的量熱能量解析度。這些改進源於使用具有極低比熱的石墨烯單層作為活性材料。200納秒的最小觀測時間常數遠低於約100微秒的零相位化時間，從而使電路量子電動力學應用於測輻射熱計。

▲ Abstract

Despite great progress in the speed and noise levels of thermal sensors, no bolometer has previously met the threshold for circuit quantum electrodynamics, which lies at a time constant of a few hundred nanoseconds and a simultaneous energy resolution of the order of 10h gigahertz (where h is the Planck constant). Here we experimentally demonstrate a bolometer that operates at this threshold, with a noise-equivalent power of 30 zeptowatts per square-root hertz, comparable to the lowest value reported so far, at a thermal time constant two orders of magnitude shorter, at 500 nanoseconds. Both of these values are measured directly on the same device, giving an accurate estimation of 30h gigahertz for the calorimetric energy resolution. These improvements stem from the use of a graphene monolayer with extremely low specific heat as the active material. The minimum observed time constant of 200 nanoseconds is well below the dephasing times of roughly 100 microseconds reported for superconducting qubits and matches the timescales of currently used readout schemes, thus enabling circuit quantum electrodynamics applications for bolometers.

生物學Biology

Active particles induce large shape deformations in giant lipid vesicles

活性顆粒在巨大的脂質囊泡中引起較大形狀變形

▲ 作者：Hanumantha Rao Vutukuri, Masoud Hoore, Clara Abaurrea-Velasco, Lennard van Buren, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2730-x

▲ 摘要

生物細胞產生複雜的結構，從內部塑造他們的膜，從而積極地感覺和回應外部刺激或探索他們的環境。

在此，我們提出了一個聯合實驗和模擬研究，證明了自我推進的顆粒封閉在巨大的單胞小泡可以誘導過多的非平衡形狀和主動膜波動。在實驗中，我們使用共焦顯微鏡探索膜對自光Janus微遊泳者施加的局部力的響應。

為了量化膜的動態變化，我們用動態三角曲面建模的薄膜殼進行了活躍布朗粒子的朗之萬動力學模擬。

最明顯的形狀變化是在低和中等的顆粒載荷下觀察到的，伴隨著繩狀突起和高度分枝的樹突結構的形成，而在高體積分數下觀察到全局變形的囊泡形狀。所得到的狀態圖預測了局部內力產生各種膜形狀的條件。

▲ Abstract

Biological cells generate intricate structures by sculpting their membrane from within to actively sense and respond to external stimuli or to explore their environment. Here we present a combined experimental and simulation study that demonstrates how self-propelled particles enclosed in giant unilamellar vesicles can induce a plethora of non-equilibrium shapes and active membrane fluctuations. Using confocal microscopy, in the experiments we explore the membrane response to local forces exerted by self-phoretic Janus microswimmers. To quantify dynamic membrane changes, we perform Langevin dynamics simulations of active Brownian particles enclosed in thin membrane shells modelled by dynamically triangulated surfaces. The most pronounced shape changes are observed at low and moderate particle loadings, with the formation of tether-like protrusions and highly branched, dendritic structures, whereas at high volume fractions globally deformed vesicle shapes are observed. The resulting state diagram predicts the conditions under which local internal forces generate various membrane shapes.

化學Chemistry

Concentric liquid reactors for chemical synthesis and separation

用於化學合成和分離的同軸液體反應器

▲ 作者：Olgierd Cybulski, Miroslaw Dygas, Barbara Mikulak-Klucznik, Marta Siek, Tomasz Klucznik, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2768-9

▲ 摘要

近年來，人們對能夠支持多步驟化學過程而無需人工處理的系統越來越感興趣。這些系統要麼基於間歇反應器的收集，要麼基於流動化學設計，兩者都需要相當大的工程努力來建立和控制。

在此，我們發展了一個不平衡的系統，其中不同的反應區自組織，可以指示整個過程序列的進展。將不同密度的多種（通常約10種，有時超過20種）互不相溶或成對互不相溶的液體放入旋轉容器中，在該容器中，它們會受到一個表面張力主導的離心力。

結果，液體組織成同心層，其厚度低至150微米，理論上達到數十微米。這些層堅固耐用，而且可以通過加速或減速旋轉來內部混合，並且每一層都可以單獨處理，允許在旋轉過程中對整個層進行添加、採樣甚至提取。

▲ Abstract

Recent years have witnessed increased interest in systems that are capable of supporting multistep chemical processes without the need for manual handling of intermediates. These systems have been based either on collections of batch reactors or on flow-chemistry designs, both of which require considerable engineering effort to set up and control. Here we develop an out-of-equilibrium system in which different reaction zones self-organize into a geometry that can dictate the progress of an entire process sequence. Multiple (routinely around 10, and in some cases more than 20) immiscible or pairwise-immiscible liquids of different densities are placed into a rotating container, in which they experience a centrifugal force that dominates over surface tension. As a result, the liquids organize into concentric layers, with thicknesses as low as 150 micrometres and theoretically reaching tens of micrometres. The layers are robust, yet can be internally mixed by accelerating or decelerating the rotation, and each layer can be individually addressed, enabling the addition, sampling or even withdrawal of entire layers during rotation.

地理學Geography

Rate of mass loss from the Greenland Ice Sheet will exceed Holocene values this century

格陵蘭冰蓋質量損失速度將在本世紀超過全新世的數值

▲ 作者：Jason P. Briner, Joshua K. Cuzzone, Jessica A. Badgeley, Nicolás E. Young, Eric J. Steig, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2742-6

▲ 摘要

格陵蘭冰蓋（GIS）正在大量消失。考慮到觀察記錄的短期性質，很難評估質量損失的歷史重要性的趨勢。

與溫室氣體濃度和全球溫度的記錄不同的是，在這些記錄中，觀測數據已經與古氣候數據集合併，在GIS質量變化率方面沒有類似的長記錄。

在此，我們通過將當前和未來GIS質量損失率置於過去12000年的自然變化背景下，揭示了本世紀GIS前所未有的質量損失。我們建立了一個高解析度的冰原模型，該模型包含了受冰核數據限制的氣候歷史集合。

模擬區域為西南綠地，其質量變化以地表質量平衡為主。結果與地理信息系統邊緣的歷史獨立年表一致。

工業化前最大的質量損失率（每個世紀高達6億噸）發生在全新世早期，與當代（公元2000年至2018年）每世紀約61000億噸的質量損失率相似。根據與低（RCP2.6）和高（RCP8.5）溫室氣體濃度軌跡相對應的典型濃度路徑（RCP），西南地理信息系統對未來質量損失的模擬預測，21世紀質量損失將在8800到359,000億噸之間。

GIS質量損失的速率超過了過去12000年的最高速率。由於西南地理信息系統的質量損失率與地理信息系統整體的質量損失率呈線性關係，因此我們的結果顯示，在本世紀地理信息系統的質量損失率將超過全新世的質量損失率。

▲ Abstract

The Greenland Ice Sheet (GIS) is losing mass at a high rate. Given the short-term nature of the observational record, it is difficult to assess the historical importance of this mass-loss trend. Unlike records of greenhouse gas concentrations and global temperature, in which observations have been merged with palaeoclimate datasets, there are no comparably long records for rates of GIS mass change. Here we reveal unprecedented mass loss from the GIS this century, by placing contemporary and future rates of GIS mass loss within the context of the natural variability over the past 12,000 years. We force a high-resolution ice-sheet model with an ensemble of climate histories constrained by ice-core data. Our simulation domain covers southwestern Greenland, the mass change of which is dominated by surface mass balance. The results agree favourably with an independent chronology of the history of the GIS margin. The largest pre-industrial rates of mass loss (up to 6,000 billion tonnes per century) occurred in the early Holocene, and were similar to the contemporary (AD 2000–2018) rate of around 6,100 billion tonnes per century. Simulations of future mass loss from southwestern GIS, based on Representative Concentration Pathway (RCP) scenarios corresponding to low (RCP2.6) and high (RCP8.5) greenhouse gas concentration trajectories, predict mass loss of between 8,800 and 35,900 billion tonnes over the twenty-first century. These rates of GIS mass loss exceed the maximum rates over the past 12,000 years. Because rates of mass loss from the southwestern GIS scale linearly with the GIS as a whole, our results indicate, with high confidence, that the rate of mass loss from the GIS will exceed Holocene rates this century.