《科学》(20210910出版)一周论文导读

发布于 2021-09-12 11:48

编译 | 李言

Science, 10 SEP 2021, VOL 373, ISSUE 6560

《科学》2021年9月10日，第373卷，6560期

材料科学Materials Science

Centrifugation and index matching yield a strong and transparent bioinspired nacreous composite

离心和指数匹配产生一种强大和透明的珠光玻璃复合材料

▲ 作者：ALI AMINI, ADELE KHAVARIFRANCOIS BARTHELAT, AND ALLEN J. EHRLICHER

▲ 链接：

https://www.science.org/doi/10.1126/science.abf0277

▲ 摘要

由于其特殊的透明度和硬度，玻璃应用在许多地方; 然而，较差的断裂性、抗冲击性和机械可靠性限制了它们的应用范围。

近年来，仿生玻璃虽然表现出了卓越的机械性能，但其光学质量仍然存在问题。在此，我们提供一种珠光玻璃复合材料，它兼具强度、韧性和透明度。将微米大小的玻璃片和聚（甲基丙烯酸甲酯）（PMMA）通过离心混合和结构化，形成致密的 PMMA玻璃层。

随后，通过将PMMA的折射率调整为玻璃的折射率并对其进行化学功能化来创建连续且无缺陷界面，从而获得透明的坚韧复合材料。这种制备方法是稳健和可扩展的，该复合材料可能在不同的应用中被证明是玻璃的替代品。

▲ 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

扭曲双层石墨烯的相关电子空穴态

▲ 作者：PETER RICKHAUS, FOLKERT K. DE VRIES, JIHANG ZHU et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abc3534

▲ 摘要

当扭曲角度接近1°时，石墨烯多层膜提供了一个了解电子相关物理的窗口。在此，我们报道了双层石墨烯扭曲到2.37°的相关电子空穴态的发现。

在这个角度上，摩尔态保留了大部分独立的双分子层特征，允许双分子层投射被门单独控制。我们利用这一性质在狭窄的孤立电子和具有良好嵌套性质的空穴带之间产生了能量重叠。

我们的测量揭示了重构费米表面有序状态的形成，与密度波态一致。这种状态可以在不引入化学掺杂剂的情况下进行调节，从而可以研究相关的电子-空穴状态及其与超导性的相互作用。

▲ 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

掺杂一维铜酸盐链中异常强烈的近邻吸引力

▲ 作者：ZHUOYU CHEN, YAO WANG, SLAVKO N. REBECTAO JIA et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abf5174

▲ 摘要

在铜酸盐中，一维链化合物为理解微观物理提供了独特的机会，这是由于可靠的理论的可用性。然而，这些材料的可控掺杂挑战限制了进展。我们报道了在大范围空穴掺杂下1D铜酸盐Ba_2-xSr_xCuO_3+δ的合成和光谱分析。

我们确定了一个突出的折叠分支，其强度与简单的哈伯德模型的预测不匹配。与声子耦合可能产生的另一种强近邻吸引，定量地解释了所有可达掺杂水平的实验。

考虑到铜酸盐在结构和量子化学上的相似性，这种引力可能在高温铜酸盐超导体中发挥同样重要的作用。

▲ 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 Ba_2-xSr_xCuO_3+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.

物理学Physics

Ultralow–switching current density multilevel phase-change memory on a flexible substrate

柔性基板上的超低开关电流密度多电平相变存储器

▲ 作者：ASIR INTISAR KHAN, ALWIN DAUS, RAISUL ISLAM et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abj1261

▲ 摘要

相变存储器（PCM）是一种很有前途的数据存储在柔性电子器件，但高开关电流和功率往往是它的弱点。在这项研究中，我们证明了在柔性超晶格PCM中每平方厘米~0.1兆安培的开关电流密度，这个值比在柔性或硅衬底上的传统PCM低一到两个数量级。

这种降低的开关电流密度是通过超晶格材料中的热限制实现的，辅以小孔型器件和热绝缘柔性衬底中的电流限制。我们的设备还显示多电平操作低电阻漂移。低开关电流和良好的电阻通断比保持在反复弯曲和循环之前、期间和之后。

这些结果为柔性电子器件的低功耗存储铺平了道路，也为传统硅基板上的PCM优化提供了关键见解。

▲ 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

奇异点的相干完美吸收

▲ 作者：CHANGQING WANG, WILLIAM R. SWEENEYA. DOUGLAS STONE AND LAN YANG

▲ 链接：

https://www.science.org/doi/10.1126/science.abj1028

▲ 摘要

最近，在光子学、声学和电子学中都观察到了奇异点，即开波系统的简并。它们主要被认为是共振的简并; 然而，与波的吸收有关的简并可以表现出明显而有趣的物理特征。

在此，我们通过耗散光学微腔吸收光谱中的工程简并来证明这种吸收奇异点。我们通过实验区分了实现吸收奇异点和谐振奇异点的条件。

此外，当调谐光损耗在吸收异常点达到完全吸收时，我们观察到它的特征，即吸收光谱中不规则展宽的线形。吸收异常点的独特散射特性为非厄米简并的基础研究和应用创造了机会。

▲ 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.

地球科学Geoscience

Hydraulic jump dynamics above supercell thunderstorms

超级单体雷暴上方的水力跳跃动力学

▲ 作者：MORGAN E O’NEILL, LEIGH ORF, GERALD M. HEYMSFIELD et al.

▲ 链接：

https://www.science.org/doi/10.1126/science.abh3857

▲ 摘要

最强的超级单体雷暴通常以砧卷云（AACP）为特征，这是平流层低层的冰和水蒸气，发生在平流层环流的下风处，在过冲深对流的背风处。

AACP来源的同温层水合作用在臭氧破坏和地表变暖中作用有限。在本研究中，我们使用由雷达观测证实的大涡模拟来理解AACP产生的物理过程。

我们发现，模拟超级单体的超冲顶部可以作为地形障碍，驱动对流层顶下游的水力跳跃，类似于风暴沿山坡向下移动，但没有固体地形。一旦开始跳跃，进入平流层深处的水蒸气每秒可能超过7吨。

▲ 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.

编辑｜宗华

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