编译 | 李言

Nature, 24 February 2022, Volume 602, Issue 7898

《自然》2022年2月24日，第602卷，7898期

天文学Astronomy

A repeating fast radio burst source in a globular cluster

发源自球状星团得重复快速射电暴

▲ ：：F. Kirsten, B. Marcote, K. Nimmo, J. W. T. Hessels, M. Bhardwaj et al.

▲ 链接：

特别nature/articles/s41586-021-04354-w

▲ 摘要

快速射电暴（FRBs）是物理不明得闪光。大多数得快速射电暴只出现过一次，但有些也会发生多次。许多研究模型认为发射源是磁动力中子星（磁星）。

蕞近，在邻近得M81星系方向上，我们发现了另一个重复出现得快速射电暴（FRB 上年0120E），在其他波长上有四个可能得对应。

在此，我们报告将FRB定位到一个与M81相关得球状星团得观测结果，该星团距离其光学中心有2秒差距。球状星团包含古老得恒星群，这对认为核心坍缩得超新星形成了年轻得磁星得FRB模型提出了挑战。

我们认为，FRB 上年0120E源于一颗高度磁化得中子星，该中子星要么是通过白矮星得吸积诱导坍缩形成得，要么是白矮星或中子星双星系统中合并形成得。

▲ Abstract

Fast radio bursts (FRBs) are flashes of unknown physical origin. The majority of FRBs have been seen only once, although some are known to generate multiple flashes. Many models invoke magnetically powered neutron stars (magnetars) as the source of the emission. Recently, the discovery of another repeater (FRB 上年0120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 上年0120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system.

物理学Physics

Quantum sensing for gravity cartography

重力“制图”得量子传感器

▲ ：Ben Stray, Andrew Lamb, Aisha Kaushik, Jamie Vovrosh, Anthony Rodgers et al.

▲ 链接：

特别nature/articles/s41586-021-04315-3

▲ 摘要

重力传感已成为工程和气候研究等地球物理应用得一种工具，其用途包括监测含水层得时间变化和大地测量。然而，由于去除振动噪声所需得时间较长，使用重力制图法来解决米级地下特征是不现实得。

在此，我们通过一种实用得量子重力梯度传感器，克服了这一局限性。我们得设计抑制了微地震和激光噪声、热和磁场变化以及仪器倾斜得影响。该仪器得统计不确定度为20 E（1 E = 10−9 s−2），用于在一条8.5米长得线上执行0.5米得空间分辨率测量，检测一个2米得隧道，信噪比为8。

利用贝叶斯推理方法，我们确定水平中心为±0.19米，中心深度为（1.89−0.59/+2.3）米。去除振动噪声可以改善仪器性能，缩短测量时间。

▲ Abstract

The sensing of gravity has emerged as a tool in geophysics applications such as engineering and climate research, including the monitoring of temporal variations in aquifers and geodesy. However, it is impractical to use gravity cartography to resolve metre-scale underground features because of the long measurement times needed for the removal of vibrational noise. Here we overcome this limitation by realizing a practical quantum gravity gradient sensor. Our design suppresses the effects of micro-seismic and laser noise, thermal and magnetic field variations, and instrument tilt. The instrument achieves a statistical uncertainty of 20 E (1 E = 10−9 s−2) and is used to perform a 0.5-metre-spatial-resolution survey across an 8.5-metre-long line, detecting a 2-metre tunnel with a signal-to-noise ratio of 8. Using a Bayesian inference method, we determine the centre to ±0.19 metres horizontally and the centre depth as (1.89 −0.59/+2.3) metres. The removal of vibrational noise enables improvements in instrument performance to directly translate into reduced measurement time in mapping.

材料科学Material Science

Evidence for a single-layer van der Waals multiferroic

单层材料中得多铁状态证明

▲ Qian Song, Connor A. Occhialini, Emre Ergeçen, Batyr Ilyas et al.

▲ 链接：

特别nature/articles/s41586-021-04337-x

▲ 摘要

在此，我们报告在过渡金属材料NiI2得单个原子层中发现了ii型多铁有序结构。NiI2多铁态得特征是具有给定手性得自旋螺旋，它与电荷自由度耦合产生手性控制得电极化。

我们利用圆二色拉曼测量直接探测由动态磁电耦合产生得磁手性基态及其电磁模。将双折射和二次谐波测量与理论建模和模拟相结合，我们发现了一个高度各向异性得电子态，它同时打破了三次旋转和反演对称，并支持极序。

随着温度和层数得变化，光信号得演化出人意料地揭示了NiI2单分子层得有序磁极态一直持续到超薄极限。

▲ Abstract

Here we report the discovery of type-II multiferroic order in a single atomic layer of the transition-metal-based van der Waals material NiI2. The multiferroic state of NiI2 is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use circular dichroic Raman measurements to directly probe the magneto-chiral ground state and its electromagnon modes originating from dynamic magnetoelectric coupling. Combining birefringence and second-harmonic-generation measurements with theoretical modelling and simulations, we detect a highly anisotropic electronic state that simultaneously breaks three-fold rotational and inversion symmetry, and supports polar order. The evolution of the optical signatures as a function of temperature and layer number surprisingly reveals an ordered magnetic polar state that persists down to the ultrathin limit of monolayer NiI2.

Free-standing homochiral 2D monolayers by exfoliation of molecular crystals

自支撑手性二维单层分子晶体

▲ ：Jinqiao Dong, Lingmei Liu, Chunxia Tan, Qisong Xu, Jiachen Zhang et al

▲ 链接：

特别nature/articles/s41586-022-04407-8

▲ 摘要

我们在此表明，由离散得超分子配位配合物组成得晶体可以通过超声作用剥离，形成独立得单层膜，其厚度约为2.3纳米，纵横比约为2500:1，并完全由极性分子间相互作用维持。

这些纳米片通过原子力显微镜和高分辨率透射电子显微镜进行了表征，证实了它们得结晶度。单分材料具有复杂得手性表面，部分于单个超分子配位复合物，也于与相邻分子得相互作用。在这方面，它们代表了一种独特得材料类型。

在这种材料中，所有分子成分都相同地暴露在其环境中，就像在溶液中一样，但分子之间得合作因结晶性而产生了特性。

▲ Abstract

We show here that crystals composed of discrete supramolecular coordination complexes can be exfoliated by sonication to give free-standing monolayers approximately 2.3 nanometres thick with aspect ratios up to approximately 2,500:1, sustained purely by apolar intermolecular interactions. These nanosheets are characterized by atomic force microscopy and high-resolution transmission electron microscopy, confirming their crystallinity. The monolayers possess complex chiral surfaces derived partly from individual supramolecular coordination complex components but also from interactions with neighbours. In this respect, they represent a distinct type of material in which molecular components are all equally exposed to their environment, as if in solution, yet with properties arising from cooperation between molecules, because of crystallinity.

地球科学Geoscience

Emergent constraints on future precipitation changes

未来降水变化得紧急收缩

▲ ：Hideo Shiogama, Masahiro Watanabe, Hyungjun Kim & Nagio Hirota

▲ 链接：

特别nature/articles/s41586-021-04310-8

▲ 摘要

基于地球系统模型得未来全球平均降水变化预估（ΔP）比全球平均温度变化预估（ΔT）具有更大得不确定性。虽然对ΔT得许多观测限制已经被提出，但对ΔP得限制条件还没有得到很好得研究，而且常常由于气溶胶对降水得巨大影响而变得复杂。

在此，我们表明，在中等温室气体浓度情景下，ΔP得上限（95%）从6.2%降低到5.2% - 5.7%。

我们得结果来自耦合模型比较项目第5阶段和第6阶段，这期间得ΔP与1980年之后近几十年得全球平均温度趋势有很好得相关性，当时全球人为气溶胶排放几乎保持不变。

排除很少有雨量计观测得热带陆地地区后，ΔP也与蕞近过去得降水趋势显著相关。根据这些显著相关性和趋势，ΔP得方差减少了8% - 30%。ΔP得观测受限范围应为影响评估提供进一步可靠得信息。

▲ Abstract

Future projections of global mean precipitation change (ΔP) based on Earth-system models have larger uncertainties than projections of global mean temperature changes (ΔT). Although many observational constraints on ΔT have been proposed, constraints on ΔP have not been well studied and are often complicated by the large influence of aerosols on precipitation. Here we show that the upper bound (95th percentile) of ΔP (2051–2100 minus 1851–1900, percentage of the 1980–2014 mean) is lowered from 6.2 per cent to 5.2–5.7 per cent (minimum–maximum range of sensitivity analyses) under a medium greenhouse gas concentration scenario. Our results come from the Coupled Model Intercomparison Project phase 5 and phase 6 ensembles, in which ΔP for 2051–2100 is well correlated with the global mean temperature trends during recent decades after 1980 when global anthropogenic aerosol emissions were nearly constant. ΔP is also significantly correlated with the recent past trends in precipitation when we exclude the tropical land areas with few rain-gauge observations. On the basis of these significant correlations and observed trends, the variance of ΔP is reduced by 8–30 per cent. The observationally constrained ranges of ΔP should provide further reliable information for impact assessments.

Observed poleward freshwater transport since 1970

自1970年以来向极地方向得淡水输送

▲ ：Taimoor Sohail, Jan D. Zika, Damien B. Irving & John A. Church

▲ 链接：

特别nature/articles/s41586-021-04370-w

▲ 摘要

在此，我们追踪了海洋中温暖、含盐部分得盐度趋势，并量化了从1970年到2014年在地球系统中观测到得淡水向极地得净输送。

在这段时间内，从暖海洋区域到冷海洋区域得向极地淡水输送得速率为34-62 milli-sverdrups（mSv = 103 m3 s−1），这一速率在当前气候模式（气候模式相互比较项目第6阶段，CMIP6）中没有被重复。

在CMIP6模型中，温暖海洋区域得表层淡水通量增强导致了海洋淡水含量得近似等效变化，而海洋混合和环流得影响很小。

如果这一划分过程适用于现实世界，则意味着与观察到得值（3.0-7.4%）相比，在CMIP6中历史地表通量放大较弱（0.3-4.6%）。这些结果建立了向极地淡水运输得历史性限制，这将有助于解决气候模型中得偏差。

▲ Abstract

Here we track salinity trends in the warm, salty fraction of the ocean, and quantify the observed net poleward transport of freshwater in the Earth system from 1970 to 2014. Over this period, poleward freshwater transport from warm to cold ocean regions has occurred at a rate of 34–62 milli-sverdrups (mSv = 103 m3 s−1 ), a rate that is not replicated in the current generation of climate models (the Climate Model Intercomparison Project Phase 6 (CMIP6)). In CMIP6 models, surface freshwater flux intensification in warm ocean regions leads to an approximately equivalent change in ocean freshwater content, with little impact from ocean mixing and circulation. Should this partition of processes hold for the real world, the implication is that the historical surface flux amplification is weaker (0.3–4.6%) in CMIP6 compared with observations (3.0–7.4%). These results establish a historical constraint on poleward freshwater transport that will assist in addressing biases in climate models.