《自然》（20240523出版）一周論文導讀

天文學Astronomy

The solar dynamo begins near the surface

太陽發電機效應始于太陽表面附近

▲ 作者：Geoffrey M. Vasil, Daniel Lecoanet, Kyle Augustson, Keaton J. Burns, Jeffrey S. Oishi, Benjamin P. Brown, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-024-07315-1

▲ 摘要：

太陽磁發電機效應周期具有獨特模式：太陽黑子出現的傳播區域位于緯度30°附近，每11年在赤道附近消失。此外，被稱為扭轉振蕩的縱向流動與太陽黑子遷移密切相關，毫無疑問具有共同原因。

與暗示這些現象深層起源的理論相反，日震學將低緯度扭轉振蕩精確定位于太陽外層的5~10%，即近太陽表面剪切層。在該區域內，向內增加的差動旋轉與極向磁場耦合，強烈暗示了磁旋轉不穩定性，這在吸積盤理論中很突出，在實驗室中亦可觀測。總之，這兩個事實引出了一個普遍的問題：太陽發電機效應是否源于近太陽表面的不穩定性。

研究組報告了強有力的肯定證據，與關注更深差旋層的傳統模型形成鮮明對比。簡單的分析估計表明，近太陽表面磁旋轉不穩定性更好地解釋了扭轉振蕩的時空尺度和推斷的太陽內部磁場振幅。

最先進的數值模擬證實了這些估計，并重現了半球磁流螺旋度定律。發電機效應產生于一個被充分理解的近太陽表面現象，這有助于對影響地球電磁基礎設施的全磁周期和空間天氣進行準確預測。

▲ Abstract：

The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating region of sunspot emergence appears around 30° latitude and vanishes near the equator every 11?years. Moreover, longitudinal flows called torsional oscillations closely shadow sunspot migration, undoubtedly sharing a common cause. Contrary to theories suggesting deep origins of these phenomena, helioseismology pinpoints low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface shear layer. Within this zone, inwardly increasing differential rotation coupled with a poloidal magnetic field strongly implicates the magneto-rotational instability, prominent in accretion-disk theory and observed in laboratory experiments. Together, these two facts prompt the general question: whether the solar dynamo is possibly a near-surface instability. Here we report strong affirmative evidence in stark contrast to traditional models focusing on the deeper tachocline. Simple analytic estimates show that the near-surface magneto-rotational instability better explains the spatiotemporal scales of the torsional oscillations and inferred subsurface magnetic field amplitudes. State-of-the-art numerical simulations corroborate these estimates and reproduce hemispherical magnetic current helicity laws. The dynamo resulting from a well-understood near-surface phenomenon improves prospects for accurate predictions of full magnetic cycles and space weather, affecting the electromagnetic infrastructure of Earth.

物理學Physics

Lithium tantalate photonic integrated circuits for volume manufacturing

可量產的鉭酸鋰光子集成電路

▲ 作者：Chengli Wang, Zihan Li, Johann Riemensberger, Grigory Lihachev, Mikhail Churaev, Wil Kao, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-024-07369-1

▲ 摘要：

基于鈮酸鋰（LiNbO3）的電-光光子集成電路（PICs）已被證明具有高Pockels系數材料的巨大能力。這實現了互補金屬-氧化物-半導體電壓水平下工作的線性和高速調制器可用于數據中心通信、高性能計算和AI光子加速器等應用。

然而，這種技術的工業應用受到單片晶圓高成本和有限晶圓尺寸的阻礙。高成本是由于在微電子領域的巨大投資推動了絕緣體上硅（SOI）光子學的采用，而在其他領域缺乏現有的高容量應用。

研究組報道了由鉭酸鋰（LiTaO3）制成的低損耗PIC，LiTaO3已在商業上用于5G射頻濾波器，因此可以低成本進行可擴展的制造，并且LiTaO3具有與LiNbO3相似甚至在某些情況下更優的性能。結果表明，使用基于深紫外（DUV）步進的制造工藝，LiTaO3可被蝕刻以創建低損耗（5.6 dB m-1）PIC。

他們演示了一種LiTaO3馬赫-曾德爾調制器（MZM），其半波電壓-長度積為1.9 V cm，電光帶寬高達40 GHz。與LiNbO3相比，LiTaO3具有極低的雙折射率，可實現所有電信頻段上的高密度電路和寬帶操作。此外，該平臺還支持生成孤子微梳。該工作為低成本和大批量的下一代光電PIC的可擴展制造鋪平了道路。

▲ Abstract：

Electro-optical photonic integrated circuits (PICs) based on lithium niobate (LiNbO3) have demonstrated the vast capabilities of materials with a high Pockels coefficient. They enable linear and high-speed modulators operating at complementary metal–oxide–semiconductor voltage levels to be used in applications including data-centre communications, high-performance computing and photonic accelerators for AI. However, industrial use of this technology is hindered by the high cost per wafer and the limited wafer size. The high cost results from the lack of existing high-volume applications in other domains of the sort that accelerated the adoption of silicon-on-insulator (SOI) photonics, which was driven by vast investment in microelectronics. Here we report low-loss PICs made of lithium tantalate (LiTaO3), a material that has already been adopted commercially for 5G radiofrequency filters and therefore enables scalable manufacturing at low cost, and it has equal, and in some cases superior, properties to LiNbO3. We show that LiTaO3 can be etched to create low-loss (5.6 dB m-1) PICs using a deep ultraviolet (DUV) stepper-based manufacturing process. We demonstrate a LiTaO3 Mach–Zehnder modulator (MZM) with a half-wave voltage–length product of 1.9 V cm and an electro-optic bandwidth of up to 40 GHz. In comparison with LiNbO3, LiTaO3 exhibits a much lower birefringence, enabling high-density circuits and broadband operation over all telecommunication bands. Moreover, the platform supports the generation of soliton microcombs. Our work paves the way for the scalable manufacture of low-cost and large-volume next-generation electro-optical PICs.

材料科學Materials Science

Selenium-alloyed tellurium oxide for amorphous p-channel transistors

硒合金氧化碲助力非晶p溝道晶體管

▲ 作者：Ao Liu, Yong-Sung Kim, Min Gyu Kim, Youjin Reo, Taoyu Zou, Taesu Choi, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-024-07360-w

▲ 摘要：

與多晶半導體相比，非晶半導體提供了固有成本效益，易于加工和統一制造。傳統的非晶氫化硅在電性能方面存在不足，亟需開發新材料。

高遷移率非晶n型金屬氧化物（如a-InGaZnO）的產生及其與薄膜晶體管（TFTs）的集成，推動了現代大面積電子器件和新一代顯示器的進步。然而，尋找類似的p型對應物頗具挑戰，阻礙了互補金屬-氧化物-半導體技術和集成電路的進展。

研究組介紹了一種非晶p型半導體的開創性設計策略，將高遷移率碲引入至非晶亞氧化碲基體，并展示了其在高性能、穩定的p溝道TFTs和互補電路中的應用。理論分析揭示了具有淺受主態的碲5p帶的離域價帶，可實現過量的空穴摻雜和輸運。

硒合金化抑制了空穴濃度，促進了p軌道的連接，實現了高性能的p溝道TFTs，其平均場效應空穴遷移率約為15 cm2 V-1 s-1，開/關電流比為106~107，且在偏置應力和環境老化下具有晶圓級均勻性和長期穩定性。這項研究代表了以低成本和工業兼容的方式建立商業上可行的非晶p溝道TFT技術和互補電子設備的關鍵一步。

▲ Abstract：

Compared to polycrystalline semiconductors, amorphous semiconductors offer inherent cost-effective, simple and uniform manufacturing. Traditional amorphous hydrogenated Si falls short in electrical properties, necessitating the exploration of new materials. The creation of high-mobility amorphous n-type metal oxides, such as a-InGaZnO, and their integration into thin-film transistors (TFTs) have propelled advancements in modern large-area electronics and new-generation displays. However, finding comparable p-type counterparts poses notable challenges, impeding the progress of complementary metal–oxide–semiconductor technology and integrated circuits. Here we introduce a pioneering design strategy for amorphous p-type semiconductors, incorporating high-mobility tellurium within an amorphous tellurium suboxide matrix, and demonstrate its use in high-performance, stable p-channel TFTs and complementary circuits. Theoretical analysis unveils a delocalized valence band from tellurium 5p bands with shallow acceptor states, enabling excess hole doping and transport. Selenium alloying suppresses hole concentrations and facilitates the p-orbital connectivity, realizing high-performance p-channel TFTs with an average field-effect hole mobility of around 15?ccm2 V-1 s-1 and on/off current ratios of 106~107, along with wafer-scale uniformity and long-term stabilities under bias stress and ambient ageing. This study represents a crucial stride towards establishing commercially viable amorphous p-channel TFT technology and complementary electronics in a low-cost and industry-compatible manner.

電子工程Electronic Engineering

Full-colour 3D holographic augmented-reality displays with metasurface waveguides

具有超表面波導的全彩3D全息增強現實顯示器

▲ 作者：Manu Gopakumar, Gun-Yeal Lee, Suyeon Choi, Brian Chao, Yifan Peng, Jonghyun Kim, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-024-07386-0

▲ 摘要：

新興空間計算系統將數字信息無縫疊加在用戶觀察到的物理環境上，從而實現了娛樂、教育、通信和培訓等各個領域的變革性體驗。然而，由于增強現實（AR）顯示器的光引擎投影光學元件體積龐大，且無法準確描繪虛擬內容的三維（3D）深度信號等因素，其廣泛采用受到限制。

研究組介紹了一種全息AR系統，使用反向設計的全彩超表面光柵、緊湊的色散補償波導幾何結構和人工智能驅動的全息算法的獨特組合來克服這些挑戰。這些元件是協同設計的，消除了空間光調制器和波導之間對龐大準直光學器件的需求，并以緊湊設備規格來呈現生動的全彩3D AR內容。

為了通過該原型提供前所未有的視覺質量，研究組開發了一種融合物理精確的波導模型與相機反饋自動校準的學習組件的創新圖像形成模型。這種獨特的納米光子超表面波導和人工智能驅動全息算法的聯合設計代表了在緊湊可穿戴設備中創建視覺上引人注目的3D AR體驗的重大進步。

▲ Abstract：

Emerging spatial computing systems seamlessly superimpose digital information on the physical environment observed by a user, enabling transformative experiences across various domains, such as entertainment, education, communication and training. However, the widespread adoption of augmented-reality (AR) displays has been limited due to the bulky projection optics of their light engines and their inability to accurately portray three-dimensional (3D) depth cues for virtual content, among other factors. Here we introduce a holographic AR system that overcomes these challenges using a unique combination of inverse-designed full-colour metasurface gratings, a compact dispersion-compensating waveguide geometry and artificial-intelligence-driven holography algorithms. These elements are co-designed to eliminate the need for bulky collimation optics between the spatial light modulator and the waveguide and to present vibrant, full-colour, 3D AR content in a compact device form factor. To deliver unprecedented visual quality with our prototype, we develop an innovative image formation model that combines a physically accurate waveguide model with learned components that are automatically calibrated using camera feedback. Our unique co-design of a nanophotonic metasurface waveguide and artificial-intelligence-driven holographic algorithms represents a significant advancement in creating visually compelling 3D AR experiences in a compact wearable device.

化學Chemistry

Observation of a promethium complex in solution

溶液中钷配合物的觀測

▲ 作者：Darren M. Driscoll, Frankie D. White, Subhamay Pramanik, Jeffrey D. Einkauf, Bruce Ravel, Dmytro Bykov, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-024-07267-6

▲ 摘要：

鑭系稀土金屬在現代技術中普遍存在，但人們對第61號元素钷（Pm）的化學性質知之甚少，Pm是一種高度放射性且難以接近的鑭系元素。盡管Pm很重要，但其在鑭系元素的實驗研究中罕有涉及，阻礙了人們對所謂鑭系元素收縮現象的全面理解：這是通用化學教科書中引用元素周期表的一個基本方面。

研究組證明了通過新合成的有機二甘醇酰胺配體在水溶液中可與147Pm放射性核素（半衰期為2.62年）穩定螯合。利用同步X射線吸收光譜和量子化學計算，研究了所得到的均配型PmIII配合物，確定了钷的配位結構和鍵距。這些基本見解使人們能夠對一整套同構鑭系元素配合物進行完整的結構研究，最終僅在實驗觀察的基礎上捕獲溶液中的鑭系收縮。

研究結果表明，在鑭系元素系列開始時鍵縮短加速，這與二甘醇酰胺顯示的分離趨勢有關。在水環境中對放射性PmIII配合物的表征加深了人們對鑭系元素內部行為以及f區元素化學和分離的理解。

▲ Abstract：

Lanthanide rare-earth metals are ubiquitous in modern technologies, but we know little about chemistry of the 61st element, promethium (Pm), a lanthanide that is highly radioactive and inaccessible. Despite its importance, Pm has been conspicuously absent from the experimental studies of lanthanides, impeding our full comprehension of the so-called lanthanide contraction phenomenon: a fundamental aspect of the periodic table that is quoted in general chemistry textbooks. Here we demonstrate a stable chelation of the 147Pm radionuclide (half-life of 2.62 years) in aqueous solution by the newly synthesized organic diglycolamide ligand. The resulting homoleptic PmIII complex is studied using synchrotron X-ray absorption spectroscopy and quantum chemical calculations to establish the coordination structure and a bond distance of promethium. These fundamental insights allow a complete structural investigation of a full set of isostructural lanthanide complexes, ultimately capturing the lanthanide contraction in solution solely on the basis of experimental observations. Our results show accelerated shortening of bonds at the beginning of the lanthanide series, which can be correlated to the separation trends shown by diglycolamides. The characterization of the radioactive PmIII complex in an aqueous environment deepens our understanding of intra-lanthanide behaviour and the chemistry and separation of the f-block elements.

Boron catalysis in a designer enzyme

人工酶中的硼催化作用

▲ 作者：Lars Longwitz, Reuben B. Leveson-Gower, Henri?tte J. Rozeboom, Andy-Mark W. H. Thunnissen & Gerard Roelfes

▲ 鏈接：

https://www.nature.com/articles/s41586-024-07391-3

▲ 摘要：

酶在提高化工生產的友好性和效率方面發揮著越來越重要的作用，但由于酶的反應機理范圍相對狹窄，其應用的多樣性嚴重落后于化學催化劑。含有非生物功能酶的創造促進了自然界經典之外的反應機制，并為完全可編程的生物催化鋪平了道路。

研究組提出了一種完全遺傳編碼的含硼酸的人工酶，其有機催化活性是天然或工程生物催化劑無法實現的。這種硼酶通過肟形成催化羥基酮的動力學拆分，其中與蛋白質支架的關鍵相互作用有助于催化。定向進化運動導致了對幾種不同底物具有天然酶樣對映體選擇性的變體。

利用X射線晶體學、高分辨率質譜（HRMS）和11B NMR波譜證實了硼酶的獨特活化模式。研究結果表明，遺傳密碼擴展可用于創建可進化的對映選擇性酶，這些酶依賴于外源性催化部分，如硼酸和通過天然或人工酶的催化混雜性無法達到的通路反應機制。

▲ Abstract：

Enzymes play an increasingly important role in improving the benignity and efficiency of chemical production, yet the diversity of their applications lags heavily behind chemical catalysts as a result of the relatively narrow range of reaction mechanisms of enzymes. The creation of enzymes containing non-biological functionalities facilitates reaction mechanisms outside nature’s canon and paves the way towards fully programmable biocatalysis. Here we present a completely genetically encoded boronic-acid-containing designer enzyme with organocatalytic reactivity not achievable with natural or engineered biocatalysts. This boron enzyme catalyses the kinetic resolution of hydroxyketones by oxime formation, in which crucial interactions with the protein scaffold assist in the catalysis. A directed evolution campaign led to a variant with natural-enzyme-like enantioselectivities for several different substrates. The unique activation mode of the boron enzyme was confirmed using X-ray crystallography, high-resolution mass spectrometry (HRMS) and 11B NMR spectroscopy. Our study demonstrates that genetic-code expansion can be used to create evolvable enantioselective enzymes that rely on xenobiotic catalytic moieties such as boronic acids and access reaction mechanisms not reachable through catalytic promiscuity of natural or engineered enzymes.