編譯 | 未玖
Science, 29 OCTOBER 2021, VOL 374, ISSUE 6567
《科學》2021年10月29日，第374卷，6567期
材料科學Materials Science
Electrically switchable metallic polymer nanoantennas
電切換金屬聚合物奈米天線
▲ 作者：JULIAN KARST, MORITZ FLOESS, MONIKA UBL, CARSTEN DINGLER, CLAUDIA MALACRIDA, TOBIAS STEINLE, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abj3433
▲ 摘要
金屬-絕緣體過渡的電切換將為整合電光有源等離子體提供一個構建塊。在這項工作中，研究組在金屬聚合物中實現了等離子體奈米天線，它們在金屬狀態下表現出明顯的局域等離子體共振。
由於電化學驅動聚合物從光學金屬轉變為絕緣體，僅透過施加±1伏的交流電壓，等離子體共振即可在高達30 Hz的影片速率頻率下完全關閉和重新啟動。
利用這一概念，研究組演示了在傳輸中具有100%對比度的電切換光束控制超表面。該方法將有助於實現基於超高效等離子體的整合有源光學器件，包括高解析度增強和虛擬現實技術。
▲ Abstract
Electrical switching of a metal-to-insulator transition would provide a building block for integrated electro-optically active plasmonics. In this work, we realize plasmonic nanoantennas from metallic polymers, which show well-pronounced localized plasmon resonances in their metallic state. As a result of the electrochemically driven optical metal-to-insulator transition of the polymer, the plasmonic resonances can be electrically switched fully off and back on at video-rate frequencies of up to 30 hertz by applying alternating voltages of only ±1 volt. With the use of this concept, we demonstrate electrically switchable beam-steering metasurfaces with a 100% contrast ratio in transmission. Our approach will help to realize ultrahigh efficiency plasmonic-based integrated active optical devices, including high-resolution augmented and virtual reality technologies.
Intrinsic 2D-XY ferromagnetism in a van der Waals monolayer
範德華單分子層中的本徵2D-XY鐵磁性
▲ 作者：AMILCAR BEDOYA-PINTO, JING-RONG JI, XAVANINDRA K. PANDEYA, PIERLUIGI GARGIANI, MANUEL VALVIDARES, PAOLO SESSI, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abd5146
▲ 摘要
低維繫統中相變的物理和普適性標度一直是人們非常感興趣的話題。近年來，神秘的長程磁有序二維（2D）材料成為人們關注的焦點。雖然平面外各向異性已被證明可穩定二維磁有序，但平面內旋轉對稱的二維磁體仍難以捉摸。
研究組構建了一個接近理想的易平面系統，即石墨烯/6H-SiC（0001）上一個單一CrCl3單層膜，並觀察到2D-XY系統具有臨界標度特性的魯棒鐵磁有序。
這些觀察結果表明，在具有XY普適性類的大面積準獨立式範德華單分子層磁體中實現了有限尺寸的Berezinski-Kosterlitz-Thouless相變。這為二維超流體自旋傳輸和拓撲磁結構提供了一個材料平臺。
▲ Abstract
The physics and universality scaling of phase transitions in low-dimensional systems has historically been a topic of great interest. Recently, two-dimensional (2D) materials exhibiting intriguing long-range magnetic order have been in the spotlight. Although an out-of-plane anisotropy has been shown to stabilize 2D magnetic order, the demonstration of a 2D magnet with in-plane rotational symmetry has remained elusive. We constructed a nearly ideal easy-plane system, a single CrCl3 monolayer on graphene/6H-SiC(0001), and observed robust ferromagnetic ordering with critical scaling characteristic of a 2D-XY system. These observations indicate the realization of a finite-size Berezinskii-Kosterlitz-Thouless phase transition in a large-area, quasi–free-standing van der Waals monolayer magnet with an XY universality class. This offers a material platform to host 2D superfluid spin transport and topological magnetic textures.
物理學Physics
Direct evidence for Cooper pairing without a spectral gap in a disordered superconductor above Tc
高於Tc的無序超導體中無譜隙庫珀對的直接證據
▲ 作者：KOEN M. BASTIAANS, DAMIANOS CHATZOPOULOS, JIAN-FENG GE, DOOHEE CHO, WILLEM O. TROMP, JAN M. VAN RUITENBEEK, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abe3987
▲ 摘要
在高於零電阻臨界溫度（Tc）的情況下，超導體中是否存在預先形成的庫珀對？人們在非常規超導體、介面超導體和無序超導體中進行了探索，但直接實驗證據仍不明確。
透過觀察散粒噪聲的增強（相當於有效電荷從一個電子電荷變為兩個電子電荷），研究組使用掃描隧道噪聲譜表明，在無序超導體氮化鈦中，溫度遠高於Tc時，預先形成的庫珀對仍存在。
研究組進一步表明，隨著溫度升高，光譜間隙會被填滿而非閉合。該結果證明存在一種溫度高於Tc的狀態，它與普通金屬非常相似，沒有（贗）能隙，但透過成對電子攜帶電荷。
▲ Abstract
The idea that preformed Cooper pairs could exist in a superconductor at temperatures higher than its zero-resistance critical temperature (Tc) has been explored for unconventional, interfacial, and disordered superconductors, but direct experimental evidence is lacking. We used scanning tunneling noise spectroscopy to show that preformed Cooper pairs exist up to temperatures much higher than Tc in the disordered superconductor titanium nitride by observing an enhancement in the shot noise that is equivalent to a change of the effective charge from one to two electron charges. We further show that the spectroscopic gap fills up rather than closes with increasing temperature. Our results demonstrate the existence of a state above Tc that, much like an ordinary metal, has no (pseudo) gap but carries charge through paired electrons.
地球科學Earth Science
Exceptional increases in fluvial sediment fluxes in a warmer and wetter High Mountain Asia
亞洲高山溫暖溼潤地區河流泥沙通量異常增加
▲ 作者：DONGFENG LI, XIXI LU, IRINA OVEREEM, DESMOND E. WALLING, JAIA SYVITSKI, ALBERT J. KETTNER, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abi9649
▲ 摘要
發源於亞洲高山的河流是世界三分之一人口的重要生命線。這些脆弱的河源現在正在經歷氣候變化、冰川融化和永久凍土融化加劇。
來自28個河源流域的觀測資料表明，在過去60年中，年徑流和年泥沙通量均大幅增加。自20世紀90年代中期以來，由於氣候變暖和溼潤，這一增長速度正在加快。
在極端氣候變化情景下，預計到2050年，來自亞洲高山地區河流的總泥沙通量將增加一倍以上。這些發現對該地區的水電、糧食和環境安全具有深遠影響。
▲ Abstract
Rivers originating in High Mountain Asia are crucial lifelines for one-third of the world’s population. These fragile headwaters are now experiencing amplified climate change, glacier melt, and permafrost thaw. Observational data from 28 headwater basins demonstrate substantial increases in both annual runoff and annual sediment fluxes across the past six decades. The increases are accelerating from the mid-1990s in response to a warmer and wetter climate. The total sediment flux from High Mountain Asia is projected to more than double by 2050 under an extreme climate change scenario. These findings have far-reaching implications for the region’s hydropower, food, and environmental security.
Global drivers of eukaryotic plankton biogeography in the sunlit ocean
日光海洋中真核浮游生物生物地理學的全球驅動因素
▲ 作者：GUILHEM SOMMERIA-KLEIN, ROMAIN WATTEAUX, FEDERICO M. IBARBALZ, JUAN JOSÉ PIERELLA KARLUSICH, DANIELE IUDICONE, CHRIS BOWLER, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abb3717
▲ 摘要
真核浮游生物是海洋生態系統的核心組成部分，具有特殊的分類和生態多樣性，但它們的生態如何與環境相互作用以推動全球分佈模式，人們知之甚少。
在這項工作中，研究組使用覆蓋所有主要海洋盆地的Tara Oceans元條形碼資料，結合分類群共現的機率模型來比較70種主要真核浮游生物群的生物地理學。
研究組揭示了生物地理變異的兩個主軸。首先，更加多樣化的群體顯示出更清晰的生物地理模式；其次，大體型的消費者依賴於海洋盆地，主要透過主海流系統，而小體型的光養生物則依賴於緯度，並遵循當地的環境條件。
該研究強調了不同浮游生物群在生物地理學上的顯著差異，並在全球範圍內探究影響它們分佈的決定因素。
▲ Abstract
Eukaryotic plankton are a core component of marine ecosystems with exceptional taxonomic and ecological diversity, yet how their ecology interacts with the environment to drive global distribution patterns is poorly understood. In this work, we use Tara Oceans metabarcoding data, which cover all major ocean basins, combined with a probabilistic model of taxon co-occurrence to compare the biogeography of 70 major groups of eukaryotic plankton. We uncover two main axes of biogeographic variation. First, more-diverse groups display clearer biogeographic patterns. Second, large-bodied consumers are structured by oceanic basins, mostly through the main current systems, whereas small-bodied phototrophs are structured by latitude and follow local environmental conditions. Our study highlights notable differences in biogeographies across plankton groups and investigates their determinants at the global scale.
經濟學Economics
Effects of land dispossession and forced migration on Indigenous peoples in North America
土地剝奪和被迫遷移對北美土著人民的影響
▲ 作者：JUSTIN FARRELL, PAUL BERNE BUROW, KATHRYN MCCONNELL, JUDE BAYHAM, KYLE WHYTE, AND GAL KOSS.
▲ 連結：
https://www.science.org/doi/10.1126/science.abe4943
▲ 摘要
剝奪土地和強迫遷移對北美土著人民的全面和長期影響是什麼？
研究組利用一個新的土著人民土地被剝奪和被迫遷移的資料集，在總體和單個部落層面上對歷史部落土地與當今部落土地的特徵進行統計比較。
結果表明，土著人民土地密度和擴張總體呈下降趨勢。土著人民被迫遷移到更容易受氣候變化風險和危害的土地上，且地下石油和天然氣資源貧乏。
農業適宜性和聯邦土地鄰近性的結果是混合的，這抑制了土著人的遷移、管理和傳統土地使用。這些發現對氣候脆弱性加劇、大面積土地減少和土地價值下降具有重大政策意義。
▲ Abstract
What are the full extent and long-term effects of land dispossession and forced migration for Indigenous peoples in North America? We leveraged a new dataset of Indigenous land dispossession and forced migration to statistically compare features of historical tribal lands to present-day tribal lands at the aggregate and individual tribe level. Results show a near-total aggregate reduction of Indigenous land density and spread. Indigenous peoples were forced to lands that are more exposed to climate change risks and hazards and are less likely to lie over valuable subsurface oil and gas resources. Agricultural suitability and federal land proximity results—which affect Indigenous movements, management, and traditional uses—are mixed. These findings have substantial policy implications related to heightened climate vulnerability, extensive land reduction, and diminished land value.
