Question

《自然》（20220310出版）一周论文导读

Answer 1

编译 | 冯维维

Nature , 10 March 2022, VOL 603, ISSUE 7900

《自然》 2022年3月10日，第603卷，7900期

物理学 Physics

AGN as potential factories for eccentric black hole mergers

偏心黑洞合并的潜在“工厂”

J. Samsing, I. Bartos, D. J. D’Orazio, Z. Haiman, B. Kocsis, N. W. C. Leigh, B. Liu, M. E. Pessah & H. Tagawa

链接：

https://www.nature.com/articles/s41586-021-04333-1

摘要

有一些不太多的证据表明，一个叫作GW190521的黑洞合并具有非零偏心。此外，组成黑洞的质量超过了恒星演化预测的极限。

这些巨大的质量可以用连续的合并来解释，这可能在活动星系核周围的气体盘中是有效的，但很难保持一个偏心轨道一直到合并，就像基础物理学认为的圆化一样。

作者研究表明，如果单黑洞和双黑洞之间的相互作用经常发生，并且相互倾斜度不超过几度，活跃的星系核盘环境就能导致过量的偏心合并。

研究进一步说明，与其他圆形合并相比，这个偏心群具有不同的黑洞自旋矢量和合并时轨道角动量之间的倾角分布，称为自旋轨道倾角。

Abstract

There is some weak evidence that the black hole merger named GW190521 had a non-zero eccentricity. In addition, the masses of the component black holes exceeded the limit predicted by stellar evolution. The large masses can be explained by successive mergers, which may be efficient in gas disks surrounding active galactic nuclei, but it is difficult to maintain an eccentric orbit all the way to the merger, as basic physics would argue for circularization. Here we show that active galactic nuclei disk environments can lead to an excess of eccentric mergers, if the interactions between single and binary black holes are frequent5 and occur with mutual inclinations of less than a few degrees. We further illustrate that this eccentric population has a different distribution of the inclination between the spin vectors of the black holes and their orbital angular momentum at merger, referred to as the spin–orbit tilt, compared with the remaining circular mergers.

Ultra-narrow optical linewidths in rare-earth molecular crystals

稀土分子晶体中的超窄光学线宽

Diana Serrano, Senthil Kumar Kuppusamy, Benoît Heinrich, Olaf Fuhr, David Hunger, Mario Ruben & Philippe Goldner

链接：

https://www.nature.com/articles/s41586-021-04316-2

摘要

稀土离子（REIs）是一种很有前途的固态系统，可以在量子水平上构建光物质界面。这取决于它们可能显示出狭窄的光学和自旋均匀线宽，或者是等价的长寿命量子态。

这使得REIs可以用于光子量子技术，如光的记忆、光微波转导和计算。然而，到目前为止，很少有晶体材料表现出足够安静的环境来充分利用REI特性。

作者报道了铕分子晶体的线宽在几万赫兹范围内，比其他分子系统的数量级更窄。他们利用这一特性来演示高效的光学自旋初始化，使用原子频率梳进行光的相干存储，以及实现量子门的离子相互作用的光学控制。

这些结果说明了稀土分子晶体作为光子量子技术的新平台的用途，该技术将高相干发射体与分子材料在组成、结构和集成能力方面无与伦比的通用性结合起来。

Abstract

Rare-earth ions (REIs) are promising solid-state systems for building light–matter interfaces at the quantum level. This relies on their potential to show narrow optical and spin homogeneous linewidths, or, equivalently, long-lived quantum states. This enables the use of REIs for photonic quantum technologies such as memories for light, optical–microwave transduction and computing. However, so far, few crystalline materials have shown an environment quiet enough to fully exploit REI properties. Here we report on europium molecular crystals that exhibit linewidths in the tens of kilohertz range, orders of magnitude narrower than those of other molecular systems. We harness this property to demonstrate efficient optical spin initialization, coherent storage of light using an atomic frequency comb, and optical control of ion–ion interactions towards implementation of quantum gates. These results illustrate the utility of rare-earth molecular crystals as a new platform for photonic quantum technologies that combines highly coherent emitters with the unmatched versatility in composition, structure and integration capability of molecular materials.

Structure of the moiré exciton captured by imaging its electron and hole

电子和空穴成像捕获摩尔激子的结构

作者：Ouri Karni, Elyse Barré, , Julien Madéo, Felipe H. da Jornada, Tony F. Heinz & Keshav M. Dani, etc.

链接：

https://www.nature.com/articles/s41586-021-04360-y

摘要

层间激子（ILXs）——电子空穴对结合在两个原子薄层半导体上——已经成为研究激子凝聚、单光子发射和其他量子信息应用的有吸引力的平台。作者在WSe2/MoS2异质结构中，捕获了结合形成ILX的两种粒子的时间分辨和动量分辨分布的图像：电子和空穴。

他们获得了ILX直径约5.2纳米的直接测量，以及其质量中心的定位。令人惊讶的是，这个大的ILX被发现固定在摩尔细胞内一个直径只有1.8纳米的区域，比激子本身的大小还小。

这种ILX的高度定位得到了贝特-萨尔皮特方程计算的支持，并证明ILX可以定位在小的摩尔单元细胞内。与大型的摩尔细胞不同，这些细胞在大区域上是均匀的，这使得量子技术可以形成局部激发的扩展阵列。

Abstract

Interlayer excitons (ILXs) — electron–hole pairs bound across two atomically thin layered semiconductors — have emerged as attractive platforms to study exciton condensation, single-photon emission and other quantum information applications. Yet, despite extensive optical spectroscopic investigations, critical information about their size, valley configuration and the influence of the moiré potential remains unknown. Here, in a WSe2/MoS2 heterostructure, we captured images of the time-resolved and momentum-resolved distribution of both of the particles that bind to form the ILX: the electron and the hole. We thereby obtain a direct measurement of both the ILX diameter of around 5.2 nm, comparable with the moiré-unit-cell length of 6.1 nm, and the localization of its centre of mass. Surprisingly, this large ILX is found pinned to a region of only 1.8 nm diameter within the moiré cell, smaller than the size of the exciton itself. This high degree of localization of the ILX is backed by Bethe–Salpeter equation calculations and demonstrates that the ILX can be localized within small moiré unit cells. Unlike large moiré cells, these are uniform over large regions, allowing the formation of extended arrays of localized excitations for quantum technology.

化学 Chemistry

Vertical MoS2 transistors with sub-1-nm gate lengths

栅长小于1纳米的二硫化钼晶体管

作者：Fan Wu, He Tian, Yang Shen, Zhan Hou, Jie Ren, Guangyang Gou, Yabin Sun, Yi Yang & Tian-Ling Ren

链接：

https://www.nature.com/articles/s41586-021-04323-3

摘要

超大尺寸晶体管是新一代电子器件发展的热点。虽然科学家已报道了原子薄度的二硫化钼（MoS2）晶体管，但制备栅长低于1纳米的器件一直是一个挑战。作者使用石墨烯层的边缘作为栅电极，演示了具有原子薄通道和物理栅长在1纳米以下的侧壁MoS2晶体管。

该方法使用化学气相沉积法生长的大面积石墨烯和二硫化钼薄膜，在2英寸的晶圆上制造侧壁晶体管。这项研究可以促进摩尔定律，为下一代电子产品缩小晶体管的尺寸。

Abstract

Ultra-scaled transistors are of interest in the development of next-generation electronic devices. Although atomically thin molybdenum disulfide (MoS2) transistors have been reported, the fabrication of devices with gate lengths below 1 nm has been challenging. Here we demonstrate side-wall MoS2 transistors with an atomically thin channel and a physical gate length of sub-1 nm using the edge of a graphene layer as the gate electrode. This work can promote Moore’s law of the scaling down of transistors for next-generation electronics.

Electron-catalysed molecular recognition

电子催化的分子识别

作者：Yang Jiao, Yunyan Qiu, Long Zhang, Wei-Guang Liu, Haochuan Mao, Hongliang Chen, Yuanning Feng, Kang Cai, Dengke Shen, Bo Song, Xiao-Yang Chen, Xuesong Li, Xingang Zhao, Ryan M. Young, Charlotte L. Stern, Michael R. Wasielewski, R. Dean Astumian, William A. Goddard III & J. Fraser Stoddart

链接：

https://www.nature.com/articles/s41586-021-04377-3

摘要

分子识别和超分子组装涵盖了分子间非共价排列现象的广泛光谱。然而，与形成共价键不同，这一过程的催化作用仅限于依赖于复杂的催化剂设计的方法。作者建立了一个通过扩展电子催化来促进分子识别的简单而通用的策略，它广泛应用于合成共价化学领域，并进入了超分子非共价化学领域。

作为该原理的证明，作者证明了大环主体和哑铃形客体之间的三自由基复合物的形成（一个在环境条件下动力学禁止的分子识别过程），可以在化学电子源的催化量的加入上大大加速。

因此，电化学方法可以在时间上控制分子识别，并在底物和配合物之间产生一个几乎任意的摩尔比，其范围介于零和平衡值之间。他们表示，这种动力学稳定的超分子系统很难用其他方法精确地获得。

电子在分子识别中作为催化剂的使用将激励化学家和生物学家 探索 可以用于微调非共价事件的策略，控制不同长度尺度的组装，并最终创造复杂物质的新形式。

Abstract

Molecular recognition and supramolecular assembly cover a broad spectrum of non-covalently orchestrated phenomena between molecules. Catalysis of such processes, however, unlike that for the formation of covalent bonds, is limited to approaches that rely on sophisticated catalyst design. Here we establish a simple and versatile strategy to facilitate molecular recognition by extending electron catalysis, which is widely applied in synthetic covalent chemistry, into the realm of supramolecular non-covalent chemistry. As a proof of principle, we show that the formation of a trisradical complex between a macrocyclic host and a dumbbell-shaped guest—a molecular recognition process that is kinetically forbidden under ambient conditions—can be accelerated substantially on the addition of catalytic amounts of a chemical electron source. It is, therefore, electrochemically possible to control the molecular recognition temporally and produce a nearly arbitrary molar ratio between the substrates and complexes ranging between zero and the equilibrium value. Such kinetically stable supramolecular systems are difficult to obtain precisely by other means. The use of the electron as a catalyst in molecular recognition will inspire chemists and biologists to explore strategies that can be used to fine-tune non-covalent events, control assembly at different length scales and ultimately create new forms of complex matter.

Au–Pd separation enhances bimetallic catalysis of alcohol oxidation

金钯分离提高了醇氧化双金属催化性能

作者：Xiaoyang Huang, Ouardia Akdim, Mark Douthwaite, Kai Wang, Liang Zhao, Richard J. Lewis, Samuel Pattisson, Isaac T. Daniel, Peter J. Miedziak, Greg Shaw, David J. Morgan, Sultan M. Althahban, Thomas E. Davies, Qian He, Fei Wang, Jile Fu, Donald Bethell, Steven McIntosh, Christopher J. Kiely & Graham J. Hutchings

链接：

https://www.nature.com/articles/s41586-022-04397-

摘要

在以氧为末端氧化剂的负载金属纳米颗粒催化氧化反应中，氧还原速率是一个限制因素。作者研究表明，通过分离双金属碳负载催化剂中的金和钯组分，可以使反应速率几乎是相应合金催化剂的两倍。

他们使用碳支持的单金属金和钯催化剂的物理混合物以及包含分离金和钯区域的双金属催化剂来证明这一点。

此外，他们用电化学方法证明，这种增强是由于在分离的金和钯位点上发生的单独氧化还原过程的耦合。这种催化效应（协同氧化还原增强）的发现为多组分多相催化剂的设计提供了一种方法。

Abstract

In oxidation reactions catalysed by supported metal nanoparticles with oxygen as the terminal oxidant, the rate of the oxygen reduction can be a limiting factor. Here we show that by separating the gold and palladium components in bimetallic carbon-supported catalysts, we can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst. We demonstrate this using physical mixtures of carbon-supported monometallic gold and palladium catalysts and a bimetallic catalyst comprising separated gold and palladium regions. Furthermore, we demonstrate electrochemically that this enhancement is attributable to the coupling of separate redox processes occurring at isolated gold and palladium sites. The discovery of this catalytic effect—a cooperative redox enhancement—offers an approach to the design of multicomponent heterogeneous catalysts.