《科学》（20201204出版）一周论文导读
编译｜冯维维
Science, 04 December 2020, Vol 370, Issue 6521
《科学》2020年12月4日，第370卷，6521期
粒子和量子物理学
Particle & Quantum Physics
Directly visualizing the momentum-forbidden dark excitons and their dynamics in atomically thin semiconductors
探测暗态激子
▲ 作者：Julien Madéo, Michael K. L. Man, Chakradhar Sahoo, Marshall Campbell, Vivek Pareek, E. Laine Wong, Abdullah Al-Mahboob, Nicholas S. Chan, Arka Karmakar, Bala Murali Krishna Mariserla, Xiaoqin Li, Tony F. Heinz, Ting Cao, Keshav M. Dani
▲ 链接：
https://science.sciencemag.org/content/370/6521/1199
▲ 摘要
半导体在激发态下产生激子，即电子-空穴对通过库仑引力结合在一起，对材料的光电性能有很大影响。尽管明亮的激子具有光学活性，但它们的暗态“兄弟”激子更难探测。
然而，它们确实通过与光和明亮的激子相互作用而影响光电特性。作者开发了一种泵浦探针光电发射技术，用于揭示激子的空间、时间和光谱动力学。
该技术在二氯化钨的二维单层薄膜中得到了证明，也适用于其他具有激子激发的半导体系统。
▲ Abstract
Excitons, electron-hole pairs held together by Coulomb attraction, can be generated in semiconductors under excitation and greatly influence the material's optoelectronic properties. Although bright excitons are optically active, their dark-state cousins have been more difficult to detect. They do, however, affect the optoelectronic properties through their interaction with light and bright excitons. Madéo et al. developed a pump-probe photoemission technique that is used reveal the spatial, temporal, and spectral dynamics of excitons. Demonstrated in two-dimensional monolayer films of tungsten diselenide, the technique could also be applicable to other semiconductor systems hosting excitonic excitations.
Super-resolution lightwave tomography of electronic bands in quantum materials
量子材料电子带的超分辨率光波层析成像
▲ 作者：M. Borsch, C. P. Schmid, L. Weigl, S. Schlauderer, N. Hofmann, C. Lange, J. T. Steiner, S. W. Koch, R. Huber, M. Kira
▲ 链接：
https://science.sciencemag.org/content/370/6521/1204
▲ 摘要
阐明量子材料的功能，如自旋价电子、拓扑和多体效应，为开发这些材料的应用提供了一条途径。
作者介绍了一种基于晶体动量梳概念的光谱技术。通过扩展测量学和超分辨率成像的频率梳的概念，他们证明了在环境条件下直接绘制量子电子结构的特性的能力。
使用这种技术结合精确的多体计算，他们能够揭示二维量子材料的层析成像。
▲ Abstract
Unraveling the functionalities of quantum materials such as spin-valley-electronic, topological, and many-body effects provides a route to exploiting these materials for applications. Borsch et al. introduce a spectroscopic technique based on the concept of crystal-momentum combs. By extending the ideas of frequency combs of metrology and superresolution imaging, they demonstrate the ability to directly map out the properties of quantum electronic structures under ambient conditions. Using this technique combined with accurate many-body computations, they were able to reveal tomographic images of two-dimensional quantum materials.
生物和仿生学
Biology & bionics
The exploitative segregation of plant roots
竞争的植物根系
▲ 作者：Ciro Cabal, Ricardo Martínez-García, Aurora de Castro Aguilar, Fernando Valladares
▲ 链接：
https://science.sciencemag.org/content/370/6521/1197
▲ 摘要
世界上大部分的植物生物量都以树根的形式存在于地下。作者开发了一个理论模型并对其进行实证检验，以解释支配根生长的规则。
植物会根据它们的邻居和竞争对手的关系来调整其根系的生长方式和位置。该模型提取了一些规则，说明在没有竞争的情况下，与相邻植物生长时的根球有何不同。
▲ Abstract
Much of the world's plant biomass exists out of sight underground in the form of roots. Cabal et al. developed a theoretical model and tested it empirically to explain the rules that govern root growth. Plants adjust how and where their roots grow according to how close neighboring—and competing—plants might be. The model extracts some of the rules about how root balls differ when grown close to neighboring plants compared with being grown in the absence of competition.
图片来源：MIKEL PONCE/science
Mechanisms of collision recovery in flying beetles and flapping-wing robots
飞行甲虫和扑翼机器人碰撞恢复机理研究
▲ 作者：Hoang Vu Phan, Hoon Cheol Park
▲ 链接：
https://science.sciencemag.org/content/370/6521/1214
▲ 摘要
甲虫的前翅变硬以保护它们的身体和后翅，它们在爬行或挖洞时的用途是众所周知的。然而，在飞行中较大的后翅在碰撞中的行为还不清楚，因为它们不容易弯曲。
作者对自由飞行的犀牛甲虫的后翅的折叠和展开机制进行了详细的研究，在这种情况下，翅膀在飞行过程中受到冲击，以模拟一个杂乱的环境。
他们发现，机翼上类似折纸的褶皱在受到冲击时可以迅速塌陷，然后弹回来，从而起到减震器和稳定器的作用。作者在一个扑翼机器人上复制了这种行为，使其能够在碰撞后安全飞行。
▲ Abstract
Beetles have hardened forewings for the protection of their bodies and hindwings, and their use during crawling or burrowing is well understood. However, the behavior of the larger hindwings during collisions in flight has not been clear because they do not readily flex. Phan and Park present a detailed study of the folding and unfolding mechanisms of the hindwings in free-flying rhinoceros beetles in which the wings were impacted during flight to simulate a cluttered environment. They found that origami-like folds in the wing could rapidly collapse on impact and then spring back, thus acting as shock absorbers and stabilizers. The authors replicated this behavior in a flapping-wing robot, enabling it to fly safely after collisions.
地质与地理
Geology & Geography
Temperature limits to deep subseafloor life in the Nankai Trough subduction zone
深海底比想象得更深、更热、更活跃
▲ 作者：Verena B. Heuer, Fumio Inagaki, Yuki Morono, Yusuke Kubo, Arthur J. Spivack, Bernhard Viehweger, Kai-Uwe Hinrichs, etc.
▲ 链接：
https://science.sciencemag.org/
▲ 摘要
海洋沉积物代表了一个巨大的微生物生态系统，但人们仍然不完全了解是什么因素塑造和限制了海底下的生命。
作者分析了日本海岸附近一个俯冲带的样本，发现微生物，特别是细菌营养细胞，随着深度和温度的增加而减少，直到海底下约600米（约为70℃）。在这个限度之下，内生孢子是常见的——细菌生命的残余和潜在的蓄水池。
再往深处是无菌区，在1000米以下是充满营养细胞的滚烫区域。在这样的深度，高浓度的醋酸盐和硫酸盐共存，也有极端嗜热产甲烷的迹象。
这些数据为打开了一扇奇妙的窗口，让人们得以了解这个极端而不适宜居住的环境，尽管它支持微生物的生存。
▲ Abstract
Marine sediments represent a massive microbial ecosystem, but we still do not fully understand what factors shape and limit life underneath the seafloor. Analyzing samples from a subduction zone off the coast of Japan, Heuer et al. found that microbial life, in particular bacterial vegetative cells, decreases as depth and temperature increases down to ∼600 meters below the seafloor, corresponding to temperatures of ∼70°C. Below this limit, endospores are common—a remnant, and a potential reservoir, of bacterial life. Deeper still is a sterile zone, and below 1000 meters is a scalding realm populated by vegetative cells. At such great depths, high concentrations of acetate and sulfate coexist, and there are also signs of hyperthermophilic methanogenesis. These data provide a fascinating window into an extreme and inhospitable environment that nonetheless supports microbial life.
Long-term collapse in fruit availability threatens Central African forest megafauna
果实减少威胁非洲草原象
▲ 作者：Emma R. Bush, Robin C. Whytock, Laila Bahaa-el-din, Stéphanie Bourgeois, Nils Bunnefeld, Anabelle W. Cardoso, Jean Thoussaint Dikangadissi, Pacôme Dimbonda, Edmond Dimoto, Josué Edzang Ndong, Kathryn J. Jeffery, David Lehmann, Loïc Makaga, Brice Momboua, Ludovic R. W. Momont, Caroline E. G. Tutin, Lee J. T. White, Alden Whittaker, Katharine Abernethy
▲ 链接：
https://science.sciencemag.org/content/370/6521/1219
▲ 摘要
非洲热带森林中的大型食草哺乳动物是水果的主要消耗者，许多树种依靠这些消耗者来传播种子。
等人对加蓬一个受保护的国家公园的水果产量进行了30年的监测，结果显示，在监测的73种植物中，水果产量下降了80%。与此同时，过去十年森林象的摄影记录表明，这些主要的食草动物的身体状况大幅下降。
这些结果表明，生态系统支持大象数量的能力正在下降，在一个仍然受到保护，不受狩猎和森林砍伐等其他威胁的环境中，这是一个令人担忧的前景。
▲ Abstract
Large mammal herbivores in African tropical forests are major consumers of fruit, and many tree species rely on these consumers for dispersal of their seeds. Bush et al. monitored fruit production over three decades in a protected national park in Gabon, showing an 80% decline across the 73 plant species monitored. At the same time, photographic records of forest elephants over the past decade indicate a substantial decline in body condition in these major herbivores. These results suggest that the capacity of the ecosystem to support the elephant population is decreasing, a worrying prospect in an environment that is still protected from other threats such as hunting and deforestation.
编辑｜宗华
排版｜李言