《自然》（20240215出版）一周論文導讀
編譯 | 馮維維
Nature, 15 FEB 2024, Volume 626 Issue 7999
《自然》2024年2月15日，第626卷，7999期
物理學Physics
Rapid spin changes around a magnetar fast radio burst
磁星周圍快速旋轉變化的快速射電暴
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-023-07012-5
▲ 摘要：
磁星是具有極高磁場（約1014高斯）的中子星，表現(xiàn)出各種各樣的X射線現(xiàn)象，如偶發(fā)的亞秒爆發(fā)、長期持續(xù)的通量增強和可變的旋轉周期導數(shù)。2020年，科學家從銀河磁星SGR 1935+2154探測到快速射電暴（FRB），類似于宇宙學毫秒持續(xù)時間的射電暴，證實了一些快速射電暴與磁星之間長期存在的關聯(lián)。
然而，快速射電暴在磁星中產(chǎn)生的機制仍不清楚。研究者報告了在大約9小時的時間間隔內(nèi)對SGR 1935+2154的兩個小故障的X射線觀測，其中包括2022年10月14日發(fā)生的一次快速射電暴。
每一個小故障都涉及到磁星自旋頻率的顯著增加，這是迄今為止觀測到的中子星旋轉中最大的突變之一。在這些小故障之間，磁星表現(xiàn)出一個快速的自旋下降階段，伴隨著持續(xù)的X射線發(fā)射和爆發(fā)速率的增加和隨后的下降。研究者假設，強烈而短暫的磁層風提供了迅速減緩恒星旋轉的扭矩。
第一個小故障的觸發(fā)因素將恒星的地殼與它的磁層結合在一起，增強了各種X射線信號，并產(chǎn)生了改變磁層條件的風，這可能會產(chǎn)生快速射電暴。
▲ 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
使用超低噪聲腔的室溫量子光力學
▲ 作者：Guanhao Huang, Alberto Beccari, Nils J. Engelsen & Tobias J. Kippenberg
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06997-3
▲ 摘要：
在室溫下，由光的量子逆作用驅動的機械運動，此前僅在光學恢復力控制振蕩器剛度的開創(chuàng)性實驗中被觀察到。對于由材料剛性控制振蕩的固態(tài)機械諧振器，由于機械質量因子低、光腔頻率波動、熱互調噪聲和光熱不穩(wěn)定性等因素，影響了諧振器振蕩的觀測。研究者利用中間系統(tǒng)的聲子工程膜克服了這些挑戰(zhàn)。
通過使用聲子晶體圖案腔鏡，他們將腔頻率噪聲降低了700倍以上。在這個超低噪聲腔中，研究者插入了一個高導熱的膜諧振器，質量因子（Q）為1.8億，采用最近開發(fā)的軟夾技術設計。
這些進步使系統(tǒng)的運行在海森堡位移傳感極限的2.5倍之內(nèi)，導致探測激光的壓縮比真空波動低1.09(1)dB。這項研究將固態(tài)宏觀振蕩器的量子控制擴展到室溫。
▲ 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
非共面反鐵磁體中格子狀自旋分裂的觀察
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-024-07023-w
▲ 摘要：
凝聚態(tài)系統(tǒng)中電子自旋的空間、動量和能量分離，指導了產(chǎn)生和操縱自旋極化電流的新裝置的開發(fā)。最近對磁性材料中一組以前被忽視的對稱操作的關注，導致了一種新型自旋分裂的出現(xiàn)，使選擇的反鐵磁體上的能帶具有巨大的和動量依賴的自旋極化。盡管有越來越多的理論預測，但這種自旋分裂的直接光譜證據(jù)仍然缺乏。
新研究為這種材料的存在提供了堅實的光譜和計算證據(jù)。在非共面反鐵磁二碲化錳（MnTe2）中，自旋的面內(nèi)分量在布里溫區(qū)的高對稱面上是反對稱的，在反鐵磁（AFM）基態(tài)中形成了格子狀的自旋織構。這種非常規(guī)的自旋模式，進一步發(fā)現(xiàn)在高溫順磁狀態(tài)下減少，源于固有的AFM順序，而不是自旋軌道耦合（SOC）。
這一發(fā)現(xiàn)證明了一種由時間反轉斷裂誘導的新型二次自旋織構，為AFM自旋電子學奠定了堅實的基礎，并為研究相關材料中的奇異量子現(xiàn)象鋪平了道路。
▲ 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獨立層中的二維鐵電渦旋圖
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06978-6
▲ 摘要：
最近在納米級鐵電體中發(fā)現(xiàn)的復雜極性拓撲的豐富，源于材料發(fā)展均勻極化的內(nèi)在趨勢，與施加在其上的電和機械邊界條件之間的微妙平衡。鐵電介質界面是模型系統(tǒng)，其中極化卷曲起源于開路樣電邊界條件，以避免極化電荷的積累，通過形成通量閉合域，在納米級水平上演變成渦狀結構。
雖然已知鐵電性與應變（均質和非均質）強烈耦合，但由于可以通過實驗實現(xiàn)的應變模式相對缺乏，機械約束對薄膜納米級鐵電性的影響相對較少。
研究者展示了具有控制扭轉角的獨立鐵電鈣鈦礦層的堆疊提供了一個機會，以一種由與扭轉相關的側向應變調制決定的方式來定制這些拓撲納米結構。此外，他們發(fā)現(xiàn)極化與應變梯度的撓性電耦合產(chǎn)生了一種特殊的極化渦和反渦模式。
這一發(fā)現(xiàn)為創(chuàng)造二維高密度渦旋晶體提供了機會，從而能夠探索以前未知的物理效應和功能。
▲ 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.
化學Chemistry
Designer phospholipid capping ligands for soft metal halide nanocrystals
軟金屬鹵化物納米晶體磷脂蓋層配體的設計
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06932-6
▲ 摘要：
膠體半導體納米晶體（NCs）在科學和光電子領域的成功離不開其表面性能。鹵化鉛鈣鈦礦NCs的功能化帶來了巨大的挑戰(zhàn)，因為它們的結構不穩(wěn)定，不像傳統(tǒng)半導體NCs的共價配體蓋層。
研究者假設，磷脂作為兩性離子表面活性劑的巨大而簡單的分子工程可以為金屬鹵化物NCs提供高度定制的表面化學。分子動力學模擬表明，配體—NC的表面親和力主要由兩性離子頭基的結構決定，特別是陰離子和陽離子部分在表面晶格位置的幾何適合度，核磁共振和傅里葉變換紅外光譜數(shù)據(jù)證實了這一點。
晶格匹配的伯銨鹽磷脂增強了有機—無機鹵化鉛鈣鈦礦（FAPbBr3和MAPbBr3）的結構和膠體完整性和無鉛金屬鹵化物NCs。有機配體尾部的分子結構決定了長期的膠體穩(wěn)定性和與各種極性溶劑的相容性，從碳氫化合物到丙酮和醇。
這些納米材料在溶液和固體中具有96%以上的光致發(fā)光量子產(chǎn)率，在單粒子水平上具有最小的光致發(fā)光間歇性，平均ON分數(shù)高達94%，并且具有明亮和高純度（約95%）的單光子發(fā)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.
氣候Climate
Global population profile of tropical cyclone exposure from 2002 to 2019
2002年至2019年熱帶氣旋暴露的全球人口概況
▲ 作者：Renzhi Jing, Sam Heft-Neal, Daniel R. Chavas, Max Griswold, Zetianyu Wang, Aaron Clark-Ginsberg, Debarati Guha-Sapir, Eran Bendavid & Zachary Wagner
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06963-z
▲ 摘要：
熱帶氣旋會對生計和人口健康產(chǎn)生深遠影響，這種影響往往會在事件發(fā)生后持續(xù)數(shù)年。描述受影響人群的人口和社會經(jīng)濟狀況以及脆弱性特征，對于評估與未來熱帶氣旋事件相關的健康和其他風險至關重要。
對熱帶氣旋影響程度的估計往往是區(qū)域性的，而不是全球性的，而且沒有考慮到人口的脆弱性。研究者將空間解決的年度人口統(tǒng)計估計與熱帶氣旋風場估計相結合，構建了2002年至2019年期間受熱帶氣旋影響人口的全球概況。
他們發(fā)現(xiàn)，每年約有5.6億人受到影響，在研究期間，在所有颶風強度中，受影響的人數(shù)都有所增加。與本世紀初相比，近年來暴露者的年齡分布已從兒童（5歲以下）轉向老年人（60歲以上）。
在同一個國家內(nèi)，遭受熱帶氣旋影響的人口比未遭受熱帶氣旋影響的人口在社會經(jīng)濟上更加貧困，這種關系在遭受更高強度風暴影響的人群中更為明顯。通過描述受影響人群的模式和脆弱性，研究結果可以幫助確定緩解戰(zhàn)略，評估熱帶氣旋的全球負擔和未來風險。
▲ 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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