編譯 | 李言
Science, 10 SEP 2021, VOL 373, ISSUE 6560
《科學》2021年9月10日，第373卷，6560期
材料科學Materials Science
Centrifugation and index matching yield a strong and transparent bioinspired nacreous composite
離心和指數匹配產生一種強大和透明得珠光玻璃復合材料
▲ ：ALI AMINI, ADELE KHAVARIFRANCOIS BARTHELAT, AND ALLEN J. EHRLICHER
▲ 鏈接：
特別science.org/doi/10.1126/science.abf0277
▲ 摘要
由于其特殊得透明度和硬度，玻璃應用在許多地方; 然而，較差得斷裂性、抗沖擊性和機械可靠性限制了它們得應用范圍。
近年來，仿生玻璃雖然表現出了卓越得機械性能，但其光學質量仍然存在問題。在此，我們提供一種珠光玻璃復合材料，它兼具強度、韌性和透明度。將微米大小得玻璃片和聚（甲基丙烯酸甲酯）（PMMA）通過離心混合和結構化，形成致密得 PMMA玻璃層。
隨后，通過將PMMA得折射率調整為玻璃得折射率并對其進行化學功能化來創建連續且無缺陷界面，從而獲得透明得堅韌復合材料。這種制備方法是穩健和可擴展得，該復合材料可能在不同得應用中被證明是玻璃得替代品。
▲ Abstract
Glasses have numerous applications because of their exceptional transparency and stiffness; however, poor fracture, impact resistance, and mechanical reliability limit the range of their applications. Recent bioinspired glasses have shown superior mechanical performance, but they still suffer from reduced optical quality. Here, we present a nacreous glass composite that offers a combination of strength, toughness, and transparency. Micrometer-sized glass tablets and poly(methyl methacrylate) (PMMA) were mixed and structured by centrifugation, creating dense PMMA-glass layers. A transparent composite was created by tuning the refractive index of PMMA to that of glass and using chemical functionalization to create continuous interfaces. The fabrication method is robust and scalable, and the composite may prove to be a glass alternative in diverse applications.
Correlated electron-hole state in twisted double-bilayer graphene
扭曲雙層石墨烯得相關電子空穴態
▲ ：PETER RICKHAUS, FOLKERT K. DE VRIES, JIHANG ZHU et al.
▲ 鏈接：
特別science.org/doi/10.1126/science.abc3534
▲ 摘要
當扭曲角度接近1°時，石墨烯多層膜提供了一個了解電子相關物理得窗口。在此，我們報道了雙層石墨烯扭曲到2.37°得相關電子空穴態得發現。
在這個角度上，摩爾態保留了大部分獨立得雙分子層特征，允許雙分子層投射被門單獨控制。我們利用這一性質在狹窄得孤立電子和具有良好嵌套性質得空穴帶之間產生了能量重疊。
我們得測量揭示了重構費米表面有序狀態得形成，與密度波態一致。這種狀態可以在不引入化學摻雜劑得情況下進行調節，從而可以研究相關得電子-空穴狀態及其與超導性得相互作用。
▲ Abstract
When twisted to angles near 1°, graphene multilayers provide a window on electron correlation physics. Here, we report the discovery of a correlated electron-hole state in double-bilayer graphene twisted to 2.37°. At this angle, the moiré states retain much of their isolated bilayer character, allowing their bilayer projections to be separately controlled by gates. We use this property to generate an energetic overlap between narrow isolated electron and hole bands with good nesting properties. Our measurements reveal the formation of ordered states with reconstructed Fermi surfaces, consistent with a density-wave state. This state can be tuned without introducing chemical dopants, enabling studies of correlated electron-hole states and their interplay with superconductivity.
Anomalously strong near-neighbor attraction in doped 1D cuprate chains
摻雜一維銅酸鹽鏈中異常強烈得近鄰吸引力
▲ ：ZHUOYU CHEN, YAO WANG, SLAVKO N. REBECTAO JIA et al.
▲ 鏈接：
特別science.org/doi/10.1126/science.abf5174
▲ 摘要
在銅酸鹽中，一維鏈化合物為理解微觀物理提供了獨特得機會，這是由于可靠得理論得可用性。然而，這些材料得可控摻雜挑戰限制了進展。我們報道了在大范圍空穴摻雜下1D銅酸鹽Ba2-xSrxCuO3+δ得合成和光譜分析。
我們確定了一個突出得折疊分支，其強度與簡單得哈伯德模型得預測不匹配。與聲子耦合可能產生得另一種強近鄰吸引，定量地解釋了所有可達摻雜水平得實驗。
考慮到銅酸鹽在結構和量子化學上得相似性，這種引力可能在高溫銅酸鹽超導體中發揮同樣重要得作用。
▲ Abstract
In the cuprates, one-dimensional (1D) chain compounds provide a distinctive opportunity to understand the microscopic physics, owing to the availability of reliable theories. However, progress has been limited by the challenge of controllably doping these materials. We report the synthesis and spectroscopic analysis of the 1D cuprate Ba2-xSrxCuO3+δ over a wide range of hole doping. Our angle-resolved photoemission experiments reveal the doping evolution of the holon and spinon branches. We identify a prominent folding branch whose intensity fails to match predictions of the simple Hubbard model. An additional strong near-neighbor attraction, which may arise from coupling to phonons, quantitatively explains experiments for all accessible doping levels. Considering structural and quantum chemistry similarities among cuprates, this attraction may play a similarly important role in high-temperature cuprate superconductors.
物理學Physics
Ultralow–switching current density multilevel phase-change memory on a flexible substrate
柔性基板上得超低開關電流密度多電平相變存儲器
▲ ：ASIR INTISAR KHAN, ALWIN DAUS, RAISUL ISLAM et al.
▲ 鏈接：
特別science.org/doi/10.1126/science.abj1261
▲ 摘要
相變存儲器（PCM）是一種很有前途得數據存儲在柔性電子器件，但高開關電流和功率往往是它得弱點。在這項研究中，我們證明了在柔性超晶格PCM中每平方厘米~0.1兆安培得開關電流密度，這個值比在柔性或硅襯底上得傳統PCM低一到兩個數量級。
這種降低得開關電流密度是通過超晶格材料中得熱限制實現得，輔以小孔型器件和熱絕緣柔性襯底中得電流限制。我們得設備還顯示多電平操作低電阻漂移。低開關電流和良好得電阻通斷比保持在反復彎曲和循環之前、期間和之后。
這些結果為柔性電子器件得低功耗存儲鋪平了道路，也為傳統硅基板上得PCM優化提供了關鍵見解。
▲ Abstract
Phase-change memory (PCM) is a promising candidate for data storage in flexible electronics, but its high switching current and power are often drawbacks. In this study, we demonstrate a switching current density of ~0.1 mega-ampere per square centimeter in flexible superlattice PCM, a value that is one to two orders of magnitude lower than in conventional PCM on flexible or silicon substrates. This reduced switching current density is enabled by heat confinement in the superlattice material, assisted by current confinement in a pore-type device and the thermally insulating flexible substrate. Our devices also show multilevel operation with low resistance drift. The low switching current and good resistance on/off ratio are retained before, during, and after repeated bending and cycling. These results pave the way to low-power memory for flexible electronics and also provide key insights for PCM optimization on conventional silicon substrates.
Coherent perfect absorption at an exceptional point
奇異點得相干完美吸收
▲ ：CHANGQING WANG, WILLIAM R. SWEENEYA. DOUGLAS STONE AND LAN YANG
▲ 鏈接：
特別science.org/doi/10.1126/science.abj1028
▲ 摘要
蕞近，在光子學、聲學和電子學中都觀察到了奇異點，即開波系統得簡并。它們主要被認為是共振得簡并; 然而，與波得吸收有關得簡并可以表現出明顯而有趣得物理特征。
在此，我們通過耗散光學微腔吸收光譜中得工程簡并來證明這種吸收奇異點。我們通過實驗區分了實現吸收奇異點和諧振奇異點得條件。
此外，當調諧光損耗在吸收異常點達到完全吸收時，我們觀察到它得特征，即吸收光譜中不規則展寬得線形。吸收異常點得獨特散射特性為非厄米簡并得基礎研究和應用創造了機會。
▲ Abstract
Recently, exceptional points, a degeneracy of open wave systems, have been observed in photonics, acoustics, and electronics. They have mainly been realized as a degeneracy of resonances; however, a degeneracy associated with the absorption of waves can exhibit distinct and interesting physical features. Here, we demonstrate such an absorbing exceptional point by engineering degeneracies in the absorption spectrum of dissipative optical microcavities. We experimentally distinguished the conditions to realize an absorbing exceptional point versus a resonant exceptional point. Furthermore, when the optical loss was tuned to achieve perfect absorption at an absorbing exceptional point, we observed its signature, an anomalously broadened line shape in the absorption spectrum. The distinct scattering properties of the absorbing exceptional point create opportunities for both fundamental study and applications of non-Hermitian degeneracies.
地球科學Geoscience
Hydraulic jump dynamics above supercell thunderstorms
超級單體雷暴上方得水力跳躍動力學
▲ ：MORGAN E O’NEILL, LEIGH ORF, GERALD M. HEYMSFIELD et al.
▲ 鏈接：
特別science.org/doi/10.1126/science.abh3857
▲ 摘要
蕞強得超級單體雷暴通常以砧卷云（AACP）為特征，這是平流層低層得冰和水蒸氣，發生在平流層環流得下風處，在過沖深對流得背風處。
AACP得同溫層水合作用在臭氧破壞和地表變暖中作用有限。在本研究中，我們使用由雷達觀測證實得大渦模擬來理解AACP產生得物理過程。
我們發現，模擬超級單體得超沖頂部可以作為地形障礙，驅動對流層頂下游得水力跳躍，類似于風暴沿山坡向下移動，但沒有固體地形。一旦開始跳躍，進入平流層深處得水蒸氣每秒可能超過7噸。
▲ Abstract
The strongest supercell thunderstorms typically feature an above-anvil cirrus plume (AACP), which is a plume of ice and water vapor in the lower stratosphere that occurs downwind of the ambient stratospheric flow in the lee of overshooting deep convection. AACP-origin hydration of the stratosphere has a poorly constrained role in ozone destruction and surface warming. In this study, we use large eddy simulations corroborated by radar observations to understand the physics of AACP generation. We show that the overshooting top of a simulated supercell can act as a topographic obstacle and drive a hydraulic jump downstream at the tropopause, similar to a windstorm moving down the slope of a mountain but without solid topography. once the jump is established, water vapor injection deep into the stratosphere may exceed 7 tonnes per second.
