《自然》（20240215出版）一周论文导读
编译 | 冯维维
Nature, 15 FEB 2024, Volume 626 Issue 7999
《自然》2024年2月15日，第626卷，7999期
物理学Physics
Rapid spin changes around a magnetar fast radio burst
磁星周围快速旋转变化的快速射电暴
▲ 作者：Chin-Ping Hu, Takuto Narita, Teruaki Enoto, George Younes, Zorawar Wadiasingh, Matthew G. Baring, Wynn C. G. Ho, Sebastien Guillot, Paul S. Ray, Tolga Güver, Kaustubh Rajwade, Zaven Arzoumanian, Chryssa Kouveliotou, Alice K. Harding & Keith C. Gendreau
▲ 链接：
https://www.nature.com/articles/s41586-023-07012-5
▲ 摘要：
磁星是具有极高磁场（约1014高斯）的中子星，表现出各种各样的X射线现象，如偶发的亚秒爆发、长期持续的通量增强和可变的旋转周期导数。2020年，科学家从银河磁星SGR 1935+2154探测到快速射电暴（FRB），类似于宇宙学毫秒持续时间的射电暴，证实了一些快速射电暴与磁星之间长期存在的关联。
然而，快速射电暴在磁星中产生的机制仍不清楚。研究者报告了在大约9小时的时间间隔内对SGR 1935+2154的两个小故障的X射线观测，其中包括2022年10月14日发生的一次快速射电暴。
每一个小故障都涉及到磁星自旋频率的显著增加，这是迄今为止观测到的中子星旋转中最大的突变之一。在这些小故障之间，磁星表现出一个快速的自旋下降阶段，伴随着持续的X射线发射和爆发速率的增加和随后的下降。研究者假设，强烈而短暂的磁层风提供了迅速减缓恒星旋转的扭矩。
第一个小故障的触发因素将恒星的地壳与它的磁层结合在一起，增强了各种X射线信号，并产生了改变磁层条件的风，这可能会产生快速射电暴。
▲ Abstract：
Magnetars are neutron stars with extremely high magnetic fields (
?1014gauss) that exhibit various X-ray phenomena such as sporadic subsecond bursts, long-term persistent flux enhancements and variable rotation-period derivative. In 2020, a fast radio burst (FRB), akin to cosmological millisecond-duration radio bursts, was detected from the Galactic magnetar SGR 1935+2154, confirming the long-suspected association between some FRBs and magnetars. However, the mechanism for FRB generation in magnetars remains unclear. Here we report the X-ray observation of two glitches in SGR 1935+2154 within a time interval of approximately nine hours, bracketing an FRB that occurred on 14 October 2022. Each glitch involved a significant increase in the magnetar’s spin frequency, being among the largest abrupt changes in neutron-star rotation observed so far. Between the glitches, the magnetar exhibited a rapid spin-down phase, accompanied by an increase and subsequent decline in its persistent X-ray emission and burst rate. We postulate that a strong, ephemeral, magnetospheric wind provides the torque that rapidly slows the star’s rotation. The trigger for the first glitch couples the star’s crust to its magnetosphere, enhances the various X-ray signals and spawns the wind that alters magnetospheric conditions that might produce the FRB.
Room-temperature quantum optomechanics using an ultralow noise cavity
使用超低噪声腔的室温量子光力学
▲ 作者：Guanhao Huang, Alberto Beccari, Nils J. Engelsen & Tobias J. Kippenberg
▲ 链接：
https://www.nature.com/articles/s41586-023-06997-3
▲ 摘要：
在室温下，由光的量子逆作用驱动的机械运动，此前仅在光学恢复力控制振荡器刚度的开创性实验中被观察到。对于由材料刚性控制振荡的固态机械谐振器，由于机械质量因子低、光腔频率波动、热互调噪声和光热不稳定性等因素，影响了谐振器振荡的观测。研究者利用中间系统的声子工程膜克服了这些挑战。
通过使用声子晶体图案腔镜，他们将腔频率噪声降低了700倍以上。在这个超低噪声腔中，研究者插入了一个高导热的膜谐振器，质量因子（Q）为1.8亿，采用最近开发的软夹技术设计。
这些进步使系统的运行在海森堡位移传感极限的2.5倍之内，导致探测激光的压缩比真空波动低1.09(1)dB。这项研究将固态宏观振荡器的量子控制扩展到室温。
▲ Abstract：
At room temperature, mechanical motion driven by the quantum backaction of light has been observed only in pioneering experiments in which an optical restoring force controls the oscillator stiffness. For solid-state mechanical resonators in which oscillations are controlled by the material rigidity, the observation of these effects has been hindered by low mechanical quality factors, optical cavity frequency fluctuations, thermal intermodulation noise and photothermal instabilities. Here we overcome these challenges with a phononic-engineered membrane-in-the-middle system. By using phononic-crystal-patterned cavity mirrors, we reduce the cavity frequency noise by more than 700-fold. In this ultralow noise cavity, we insert a membrane resonator with high thermal conductance and a quality factor (Q) of 180 million, engineered using recently developed soft-clamping techniques. These advances enable the operation of the system within a factor of 2.5 of the Heisenberg limit for displacement sensing8, leading to the squeezing of the probe laser by 1.09(1)dB below the vacuum fluctuations. Moreover, the long thermal decoherence time of the membrane oscillator (30 vibrational periods) enables us to prepare conditional displaced thermal states of motion with an occupation of 0.97(2) phonons using a multimode Kalman filter. Our work extends the quantum control of solid-state macroscopic oscillators to room temperature.
Observation of plaid-like spin splitting in a noncoplanar antiferromagnet
非共面反铁磁体中格子状自旋分裂的观察
▲ 作者：Yu-Peng Zhu, Xiaobing Chen, Xiang-Rui Liu, Yuntian Liu, Pengfei Liu, Heming Zha, Gexing Qu, Caiyun Hong, Jiayu Li, Zhicheng Jiang, Xiao-Ming Ma, Yu-Jie Hao, Ming-Yuan Zhu, Wenjing Liu, Meng Zeng, Sreehari Jayaram, Malik Lenger, Jianyang Ding, Shu Mo, Kiyohisa Tanaka, Masashi Arita, Zhengtai Liu, Mao Ye, Dawei Shen, …Chang Liu
▲ 链接：
https://www.nature.com/articles/s41586-024-07023-w
▲ 摘要：
凝聚态系统中电子自旋的空间、动量和能量分离，指导了产生和操纵自旋极化电流的新装置的开发。最近对磁性材料中一组以前被忽视的对称操作的关注，导致了一种新型自旋分裂的出现，使选择的反铁磁体上的能带具有巨大的和动量依赖的自旋极化。尽管有越来越多的理论预测，但这种自旋分裂的直接光谱证据仍然缺乏。
新研究为这种材料的存在提供了坚实的光谱和计算证据。在非共面反铁磁二碲化锰（MnTe2）中，自旋的面内分量在布里温区的高对称面上是反对称的，在反铁磁（AFM）基态中形成了格子状的自旋织构。这种非常规的自旋模式，进一步发现在高温顺磁状态下减少，源于固有的AFM顺序，而不是自旋轨道耦合（SOC）。
这一发现证明了一种由时间反转断裂诱导的新型二次自旋织构，为AFM自旋电子学奠定了坚实的基础，并为研究相关材料中的奇异量子现象铺平了道路。
▲ Abstract：
Spatial, momentum and energy separation of electronic spins in condensed-matter systems guides the development of new devices in which spin-polarized current is generated and manipulated. Recent attention on a set of previously overlooked symmetry operations in magnetic materials leads to the emergence of a new type of spin splitting, enabling giant and momentum-dependent spin polarization of energy bands on selected antiferromagnets. Despite the ever-growing theoretical predictions, the direct spectroscopic proof of such spin splitting is still lacking. Here we provide solid spectroscopic and computational evidence for the existence of such materials. In the noncoplanar antiferromagnet manganese ditelluride (MnTe2), the in-plane components of spin are found to be antisymmetric about the high-symmetry planes of the Brillouin zone, comprising a plaid-like spin texture in the antiferromagnetic (AFM) ground state. Such an unconventional spin pattern, further found to diminish at the high-temperature paramagnetic state, originates from the intrinsic AFM order instead of spin–orbit coupling (SOC). Our finding demonstrates a new type of quadratic spin texture induced by time-reversal breaking, placing AFM spintronics on a firm basis and paving the way for studying exotic quantum phenomena in related materials.
A 2D ferroelectric vortex pattern in twisted BaTiO3 freestanding layers
扭曲BaTiO3独立层中的二维铁电涡旋图
▲ 作者：G. Sánchez-Santolino, V. Rouco, S. Puebla, H. Aramberri, V. Zamora, M. Cabero, F. A. Cuellar, C. Munuera, F. Mompean, M. Garcia-Hernandez, A. Castellanos-Gomez, J. íiguez, C. Leon & J. Santamaria
▲ 链接：
https://www.nature.com/articles/s41586-023-06978-6
▲ 摘要：
最近在纳米级铁电体中发现的复杂极性拓扑的丰富，源于材料发展均匀极化的内在趋势，与施加在其上的电和机械边界条件之间的微妙平衡。铁电介质界面是模型系统，其中极化卷曲起源于开路样电边界条件，以避免极化电荷的积累，通过形成通量闭合域，在纳米级水平上演变成涡状结构。
虽然已知铁电性与应变（均质和非均质）强烈耦合，但由于可以通过实验实现的应变模式相对缺乏，机械约束对薄膜纳米级铁电性的影响相对较少。
研究者展示了具有控制扭转角的独立铁电钙钛矿层的堆叠提供了一个机会，以一种由与扭转相关的侧向应变调制决定的方式来定制这些拓扑纳米结构。此外，他们发现极化与应变梯度的挠性电耦合产生了一种特殊的极化涡和反涡模式。
这一发现为创造二维高密度涡旋晶体提供了机会，从而能够探索以前未知的物理效应和功能。
▲ Abstract：
The wealth of complex polar topologies recently found in nanoscale ferroelectrics results from a delicate balance between the intrinsic tendency of the materials to develop a homogeneous polarization and the electric and mechanical boundary conditions imposed on them. Ferroelectric–dielectric interfaces are model systems in which polarization curling originates from open circuit-like electric boundary conditions, to avoid the build-up of polarization charges through the formation of flux-closure domains that evolve into vortex-like structures at the nanoscale level. Although ferroelectricity is known to couple strongly with strain (both homogeneous18 and inhomogeneous), the effect of mechanical constraints on thin-film nanoscale ferroelectrics has been comparatively less explored because of the relative paucity of strain patterns that can be implemented experimentally. Here we show that the stacking of freestanding ferroelectric perovskite layers with controlled twist angles provides an opportunity to tailor these topological nanostructures in a way determined by the lateral strain modulation associated with the twisting. Furthermore, we find that a peculiar pattern of polarization vortices and antivortices emerges from the flexoelectric coupling of polarization to strain gradients. This finding provides opportunities to create two-dimensional high-density vortex crystals that would enable us to explore previously unknown physical effects and functionalities.
化学Chemistry
Designer phospholipid capping ligands for soft metal halide nanocrystals
软金属卤化物纳米晶体磷脂盖层配体的设计
▲ 作者：Viktoriia Morad, Andriy Stelmakh, Mariia Svyrydenko, Leon G. Feld, Simon C. Boehme, Marcel Aebli, Joel Affolter, Christoph J. Kaul, Nadine J. Schrenker, Sara Bals, Yesim Sahin, Dmitry N. Dirin, Ihor Cherniukh, Gabriele Raino, Andrij Baumketner & Maksym V. Kovalenko
▲ 链接：
https://www.nature.com/articles/s41586-023-06932-6
▲ 摘要：
胶体半导体纳米晶体（NCs）在科学和光电子领域的成功离不开其表面性能。卤化铅钙钛矿NCs的功能化带来了巨大的挑战，因为它们的结构不稳定，不像传统半导体NCs的共价配体盖层。
研究者假设，磷脂作为两性离子表面活性剂的巨大而简单的分子工程可以为金属卤化物NCs提供高度定制的表面化学。分子动力学模拟表明，配体—NC的表面亲和力主要由两性离子头基的结构决定，特别是阴离子和阳离子部分在表面晶格位置的几何适合度，核磁共振和傅里叶变换红外光谱数据证实了这一点。
晶格匹配的伯铵盐磷脂增强了有机—无机卤化铅钙钛矿（FAPbBr3和MAPbBr3）的结构和胶体完整性和无铅金属卤化物NCs。有机配体尾部的分子结构决定了长期的胶体稳定性和与各种极性溶剂的相容性，从碳氢化合物到丙酮和醇。
这些纳米材料在溶液和固体中具有96%以上的光致发光量子产率，在单粒子水平上具有最小的光致发光间歇性，平均ON分数高达94%，并且具有明亮和高纯度（约95%）的单光子发射。
▲ Abstract：
The success of colloidal semiconductor nanocrystals (NCs) in science and optoelectronics is inextricable from their surfaces. The functionalization of lead halide perovskite NCs poses a formidable challenge because of their structural lability, unlike the well-established covalent ligand capping of conventional semiconductor NCs. We posited that the vast and facile molecular engineering of phospholipids as zwitterionic surfactants can deliver highly customized surface chemistries for metal halide NCs. Molecular dynamics simulations implied that ligand–NC surface affinity is primarily governed by the structure of the zwitterionic head group, particularly by the geometric fitness of the anionic and cationic moieties into the surface lattice sites, as corroborated by the nuclear magnetic resonance and Fourier-transform infrared spectroscopy data. Lattice-matched primary-ammonium phospholipids enhance the structural and colloidal integrity of hybrid organic–inorganic lead halide perovskites (FAPbBr3 and MAPbBr3 (FA, formamidinium; MA, methylammonium)) and lead-free metal halide NCs. The molecular structure of the organic ligand tail governs the long-term colloidal stability and compatibility with solvents of diverse polarity, from hydrocarbons to acetone and alcohols. These NCs exhibit photoluminescence quantum yield of more than 96% in solution and solids and minimal photoluminescence intermittency at the single particle level with an average ON fraction as high as 94%, as well as bright and high-purity (about 95%) single-photon emission.
气候Climate
Global population profile of tropical cyclone exposure from 2002 to 2019
2002年至2019年热带气旋暴露的全球人口概况
▲ 作者：Renzhi Jing, Sam Heft-Neal, Daniel R. Chavas, Max Griswold, Zetianyu Wang, Aaron Clark-Ginsberg, Debarati Guha-Sapir, Eran Bendavid & Zachary Wagner
▲ 链接：
https://www.nature.com/articles/s41586-023-06963-z
▲ 摘要：
热带气旋会对生计和人口健康产生深远影响，这种影响往往会在事件发生后持续数年。描述受影响人群的人口和社会经济状况以及脆弱性特征，对于评估与未来热带气旋事件相关的健康和其他风险至关重要。
对热带气旋影响程度的估计往往是区域性的，而不是全球性的，而且没有考虑到人口的脆弱性。研究者将空间解决的年度人口统计估计与热带气旋风场估计相结合，构建了2002年至2019年期间受热带气旋影响人口的全球概况。
他们发现，每年约有5.6亿人受到影响，在研究期间，在所有飓风强度中，受影响的人数都有所增加。与本世纪初相比，近年来暴露者的年龄分布已从儿童（5岁以下）转向老年人（60岁以上）。
在同一个国家内，遭受热带气旋影响的人口比未遭受热带气旋影响的人口在社会经济上更加贫困，这种关系在遭受更高强度风暴影响的人群中更为明显。通过描述受影响人群的模式和脆弱性，研究结果可以帮助确定缓解战略，评估热带气旋的全球负担和未来风险。
▲ Abstract：
Tropical cyclones have far-reaching impacts on livelihoods and population health that often persist years after the event. Characterizing the demographic and socioeconomic profile and the vulnerabilities of exposed populations is essential to assess health and other risks associated with future tropical cyclone events. Estimates of exposure to tropical cyclones are often regional rather than global and do not consider population vulnerabilities. Here we combine spatially resolved annual demographic estimates with tropical cyclone wind fields estimates to construct a global profile of the populations exposed to tropical cyclones between 2002 and 2019. We find that approximately 560 million people are exposed yearly and that the number of people exposed has increased across all cyclone intensities over the study period. The age distribution of those exposed has shifted away from children (less than 5 years old) and towards older people (more than 60 years old) in recent years compared with the early 2000s. Populations exposed to tropical cyclones are more socioeconomically deprived than those unexposed within the same country, and this relationship is more pronounced for people exposed to higher-intensity storms. By characterizing the patterns and vulnerabilities of exposed populations, our results can help identify mitigation strategies and assess the global burden and future risks of tropical cyclones.
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