Nature, 30 January 2025, Volume 637, Issue 8048
《自然》2025年1月30日，第637卷，8048期
物理學Physics
Ultrabroadband integrated electro-optic frequency comb in lithium tantalate
鉭酸鋰中超寬帶集成電光頻率梳
▲ 作者：Junyin Zhang, Chengli Wang, Connor Denney, Johann Riemensberger, Grigory Lihachev, Jianqi Hu, Wil Kao, Terence Blésin, Nikolai Kuznetsov, Zihan Li, Mikhail Churaev, Xin Ou, Gabriel Santamaria-Botello & Tobias J. Kippenberg
▲ 鏈接：https://www.nature.com/articles/s41586-024-08354-4
▲ 摘要：基于Kerr參數振蕩的集成頻率梳發生器已經產生了芯片級、千兆赫間隔的梳，具有跨超大規模電信、低噪聲微波合成、光探測和測距以及天體物理光譜儀校準的新應用。鈮酸鋰（LiNbO3）光子集成電路（PICs）的最新進展推動了芯片規模的電光（EO）頻率梳，提供精確的梳線定位和簡單的操作，而不依賴于形成耗散克爾孤子。然而，由于驅動非諧振電容電極所需的微波功率大，以及LiNbO3的強固有雙折射，目前集成EO梳子的光譜覆蓋范圍有限。
研究者通過集成三重諧振結構克服了這兩個挑戰，將單片微波集成電路與基于最近出現的薄膜LiTaO3的PICs相結合。與傳統的非諧振微波設計相比，通過共振增強的EO相互作用和減少的雙折射，研究實現了4倍的梳子跨度擴展和16倍的功率降低。在混合集成激光二極管的驅動下，梳子的跨度超過450納米（超過60太赫茲），有2000多條線，而發生器的占地面積僅為1平方厘米。
此外，研究者還觀察到強EO耦合導致梳子存在范圍增加，接近光學微諧振器的全自由光譜范圍。超寬帶梳狀發生器與失諧不確定操作相結合，可以推進芯片級光譜分析和超低噪聲毫米波合成，并解鎖八度跨度的EO梳狀器。微波和光子協同設計的方法可以擴展到廣泛的集成光電應用。
▲ Abstract：The integrated frequency comb generator based on Kerr parametric oscillation1 has led to chip-scale, gigahertz-spaced combs with new applications spanning hyperscale telecommunications, low-noise microwave synthesis, light detection and ranging, and astrophysical spectrometer calibration. Recent progress in lithium niobate (LiNbO3) photonic integrated circuits (PICs) has resulted in chip-scale, electro-optic (EO) frequency combs, offering precise comb-line positioning and simple operation without relying on the formation of dissipative Kerr solitons. However, current integrated EO combs face limited spectral coverage due to the large microwave power required to drive the non-resonant capacitive electrodes and the strong intrinsic birefringence of LiNbO3. Here we overcome both challenges with an integrated triply resonant architecture, combining monolithic microwave integrated circuits with PICs based on the recently emerged thin-film lithium tantalate (LiTaO3). With resonantly enhanced EO interaction and reduced birefringence in LiTaO3, we achieve a fourfold comb span extension and a 16-fold power reduction compared to the conventional, non-resonant microwave design. Driven by a hybrid integrated laser diode, the comb spans over 450?nm (more than 60?THz) with more than 2,000 lines, and the generator fits within a compact 1-cm2 footprint. We additionally observe that the strong EO coupling leads to an increased comb existence range approaching the full free spectral range of the optical microresonator. The ultra-broadband comb generator, combined with detuning-agnostic operation, could advance chip-scale spectrometry and ultra-low-noise millimetre wave synthesis and unlock octave-spanning EO combs. The methodology of co-designing microwave and photonics can be extended to a wide range of integrated EOs applications.
Moiré-driven topological electronic crystals in twisted graphene
扭曲石墨烯中摩爾驅動的拓撲電子晶體
▲ 作者：Ruiheng Su, Dacen Waters, Boran Zhou, Kenji Watanabe, Takashi Taniguchi, Ya-Hui Zhang, Matthew Yankowitz & Joshua Folk
▲ 鏈接：https://www.nature.com/articles/s41586-024-08239-6
▲摘要：在稀薄的二維電子氣體中，庫侖相互作用可以穩定維格納晶體的形成。雖然維格納晶體在拓撲上是微不足道的，但據預測，部分填充帶中的電子可以自發地打破連續的平移對稱性和時間反轉對稱性，從而產生一種被稱為反常霍爾晶體的拓撲電子晶體。
研究者報告了扭曲的雙層—三層石墨烯中異?；魻柧w的廣義版本的特征，其形成是由莫爾阱勢驅動的。晶體形成于每4個摩爾粒子（ν=1/4）有1個電子的帶填充，使單位細胞面積增加了4倍，與整數量子反常霍爾效應相一致。
態的陳數是特別可調的，它可以在電場和磁場的作用下在+1和-1之間可逆地切換。其他幾個拓撲電子晶體出現在適度的磁場中，起源于ν=1/3,1/2,2/3和3/2。相互作用修飾能帶的量子幾何可能與原始母能帶的量子幾何非常不同，這使得可能在未來發現相關驅動的拓撲現象。
▲ Abstract：In a dilute two-dimensional electron gas, Coulomb interactions can stabilize the formation of a Wigner crystal. Although Wigner crystals are topologically trivial, it has been predicted that electrons in a partially filled band can break continuous translational symmetry and time-reversal symmetry spontaneously, resulting in a type of topological electron crystal known as an anomalous Hall crystal. Here we report signatures of a generalized version of the anomalous Hall crystal in twisted bilayer–trilayer graphene, whose formation is driven by the moiré potential. The crystal forms at a band filling of one electron per four moiré unit cells (ν?=?1/4) and quadruples the unit-cell area, coinciding with an integer quantum anomalous Hall effect. The Chern number of the state is exceptionally tunable, and it can be switched reversibly between +1 and ?1 by electric and magnetic fields. Several other topological electronic crystals arise in a modest magnetic field, originating from ν?=?1/3, 1/2, 2/3 and 3/2. The quantum geometry of the interaction-modified bands is likely to be very different from that of the original parent band, which enables possible future discoveries of correlation-driven topological phenomena.
Synthesis of a semimetallic Weyl ferromagnet with point Fermi surface
具有點費米表面的半金屬Weyl鐵磁體的合成
▲ 作者：Ilya Belopolski, Ryota Watanabe, Yuki Sato, Ryutaro Yoshimi, Minoru Kawamura, Soma Nagahama, Yilin Zhao, Sen Shao, Yuanjun Jin, Yoshihiro Kato, Yoshihiro Okamura, Xiao-Xiao Zhang, Yukako Fujishiro, Youtarou Takahashi, Max Hirschberger, Atsushi Tsukazaki, Kei S. Takahashi, Ching-Kai Chiu, Guoqing Chang, Masashi Kawasaki, Naoto Nagaosa & Yoshinori Tokura
▲ 鏈接：https://www.nature.com/articles/s41586-024-08330-y
▲ 摘要：由新興的拓撲費米子控制的量子材料已經成為物理學的基石。石墨烯中的狄拉克費米子構成了摩爾量子物質的基礎，磁拓撲絕緣體中的狄拉克費米子使得量子反?；魻栃≦AH）的發現成為可能。相比之下，很少有材料的電磁響應是由涌現的Weyl費米子主導的。幾乎所有已知的Weyl材料絕大多數都是金屬，并且在很大程度上由無關的常規電子控制。
這項研究從理論上預測并在實驗上觀察了范德華（Cr,Bi）2Te3中的半金屬Weyl鐵磁體。在輸運中，他們發現了一個大于0.5的記錄體異?；魻柦且约胺墙饘匐妼剩@是一個與傳統鐵磁體截然不同的制度。結合對稱性分析，研究數據表明一個由兩個Weyl點組成的半金屬費米表面，具有超過體布里淵區線性尺寸75%的巨大分離，并且沒有其他電子態。
研究者使用最先進的晶體合成技術，廣泛調整電子結構，使其能夠湮滅Weyl狀態，并可視化一個獨特的拓撲相圖，顯示廣泛的陳氏絕緣，Weyl半金屬和磁性半導體區域。研究者表示，對半金屬Weyl鐵磁體的觀察為研究新的相關態和非線性現象以及零磁場Weyl自旋電子和光學器件提供了一條途徑。
▲ Abstract：Quantum materials governed by emergent topological fermions have become a cornerstone of physics. Dirac fermions in graphene form the basis for moiré quantum matter and Dirac fermions in magnetic topological insulators enabled the discovery of the quantum anomalous Hall (QAH) effect. By contrast, there are few materials whose electromagnetic response is dominated by emergent Weyl fermions. Nearly all known Weyl materials are overwhelmingly metallic and are largely governed by irrelevant, conventional electrons. Here we theoretically predict and experimentally observe a semimetallic Weyl ferromagnet in van der Waals（Cr,Bi）2Te3. In transport, we find a record bulk anomalous Hall angle of greater than 0.5 along with non-metallic conductivity, a regime that is strongly distinct from conventional ferromagnets. Together with symmetry analysis, our data suggest a semimetallic Fermi surface composed of two Weyl points, with a giant separation of more than 75% of the linear dimension of the bulk Brillouin zone, and no other electronic states. Using state-of-the-art crystal-synthesis techniques, we widely tune the electronic structure, allowing us to annihilate the Weyl state and visualize a unique topological phase diagram exhibiting broad Chern insulating, Weyl semimetallic and magnetic semiconducting regions. Our observation of a semimetallic Weyl ferromagnet offers an avenue towards new correlated states and nonlinear phenomena, as well as zero-magnetic-field Weyl spintronic and optical devices.
Enhanced energy storage in antiferroelectrics via antipolar frustration
通過反極性挫折增強反鐵電體的能量存儲
▲ 作者：Bingbing Yang, Yiqian Liu, Ru-Jian Jiang, Shun Lan, Su-Zhen Liu, Zhifang Zhou, Lvye Dou, Min Zhang, Houbing Huang, Long-Qing Chen, Yin-Lian Zhu, Shujun Zhang, Xiu-Liang Ma, Ce-Wen Nan & Yuan-Hua Lin
▲ 鏈接：https://www.nature.com/articles/s41586-024-08505-7
▲摘要：介質儲能電容器充放電速度快、可靠性高，在尖端電子電氣設備中發揮著重要作用。為了追求電容器的小型化和集成化，電介質必須提供高能量密度和效率。具有反平行偶極子結構的反鐵電體由于其在場致鐵電態中可忽略的剩余極化和高的最大極化而在高性能能量存儲中具有重要的意義。然而，低反鐵電—鐵電相變場和伴隨的大磁滯損耗會降低能量密度和可靠性。
在相場模擬的指導下，研究者提出了一種新的策略，通過加入非極性或極性成分來挫敗反鐵電體中的反極性有序。實驗表明，該方法有效地調節了反鐵電—鐵電相變場，同時減小了磁滯損耗。在基于PbZrO3的薄膜中，他們在5.51 MV cm?1的電場下實現了189 J cm?3的反鐵電體中創紀錄的高能量密度以及81%的高效率，可與最先進的儲能介質相媲美。掃描透射電子顯微鏡的原子尺度表征直接揭示了分散的非極性區阻礙了遠程反極性有序，有助于提高性能。這種策略為操縱極化分布和提高反鐵電體的儲能性能提供了新的機會。
▲ Abstract：Dielectric-based energy storage capacitors characterized with fast charging and discharging speed and reliability play a vital role in cutting-edge electrical and electronic equipment. In pursuit of capacitor miniaturization and integration, dielectrics must offer high energy density and efficiency. Antiferroelectrics with antiparallel dipole configurations have been of significant interest for high-performance energy storage due to their negligible remanent polarization and high maximum polarization in the field-induced ferroelectric state. However, the low antiferroelectric–ferroelectric phase-transition field and accompanying large hysteresis loss deteriorate energy density and reliability. Here, guided by phase-field simulations, we propose a new strategy to frustrate antipolar ordering in antiferroelectrics by incorporating non-polar or polar components. Our experiments demonstrate that this approach effectively tunes the antiferroelectric–ferroelectric phase-transition fields and simultaneously reduces hysteresis loss. In PbZrO3-based films, we hence realized a record high energy density among all antiferroelectrics of 189?J?cm?3 along with a high efficiency of 81% at an electric field of 5.51?MV?cm?1, which rivals the most state-of-the-art energy storage dielectrics. Atomic-scale characterization by scanning transmission electron microscopy directly revealed that the dispersed non-polar regions frustrate the long-range antipolar ordering, which contributes to the improved performance. This strategy presents new opportunities to manipulate polarization profiles and enhance energy storage performances in antiferroelectrics.
化學Chemistry
Durable all-inorganic perovskite tandem photovoltaics
耐用的全無機鈣鈦礦串聯光伏電池
▲ 作者：Chenghao Duan, Kaicheng Zhang, Zijian Peng, Shiang Li, Feilin Zou, Feng Wang, Jiong Li, Zheng Zhang, Chang Chen, Qiliang Zhu, Jianhang Qiu, Xinhui Lu, Ning Li, Liming Ding, Christoph J. Brabec, Feng Gao & Keyou Yan
▲ 鏈接：https://www.nature.com/articles/s41586-024-08432-7
▲ 摘要：用無機陽離子（如Cs+）取代有機陽離子（如甲基銨和甲脒）制備全無機鈣鈦礦是提高鈣鈦礦太陽能電池（PSCs）長期光穩定性和熱穩定性的有效概念。因此，無機鈣鈦礦串聯太陽能電池（IPTSCs）是打破效率瓶頸和解決穩定性問題的有希望的候選者。然而，由于錫離子誘導的較差的薄膜形成和深阱狀態，在制備雙端（2T）IPTSC方面仍然存在挑戰。
研究者采用對甲苯磺酰肼（PTSH）的配體進化（LE）策略來調節無機窄帶隙（NBG）鈣鈦礦中的薄膜形成并消除深層陷阱，從而成功開發了2T IPTSC。IPTSC在最大功率點跟蹤下具有卓越的耐用性，在65°C和85°C下分別保持80%的初始效率1510小時和800小時。研究闡明了LE有意利用無機NBG鈣鈦礦生長的多種作用，有望為開發高效穩定的IPTSC提供有洞察力的指導。
▲ Abstract：All-inorganic perovskites prepared by substituting the organic cations (for example, methylammonium and formamidinium) with inorganic cations (for example, Cs+) are effective concepts to enhance the long-term photostability and thermal stability of perovskite solar cells (PSCs). Hence, inorganic perovskite tandem solar cells (IPTSCs) are promising candidates for breaking the efficiency bottleneck and addressing the stability issue, too. However, challenges remain in fabricating two-terminal (2T) IPTSCs due to the inferior film formation and deep trap states induced by tin cations. Here a ligand evolution (LE) strategy with p-toluenesulfonyl hydrazide (PTSH) is used to regulate film formation and eliminate deep traps in inorganic narrow-bandgap (NBG) perovskites, enabling the successful development of 2T IPTSCs. IPTSCs are engineered to deliver remarkable durability under maximum power point (MPP) tracking, maintaining 80% of their initial efficiency at 65?°C for 1,510 h and at 85?°C for 800?h. We elucidate that LE deliberately leverages multiple roles for inorganic NBG perovskite growth and anticipate that our study provides an insightful guideline for developing high-efficiency and stable IPTSCs.
生物學Biology
Sleep microstructure organizes memory replay
睡眠微觀結構組織記憶重放
▲ 作者：Hongyu Chang, Wenbo Tang, Annabella M. Wulf, Thokozile Nyasulu, Madison E. Wolf, Antonio Fernandez-Ruiz & Azahara Oliva
▲ 鏈接：https://www.nature.com/articles/s41586-024-08340-w
▲摘要：最近獲得的記憶在睡眠時在海馬體中被重新激活，這是鞏固記憶的第一步。這一過程伴隨著海馬體對先前記憶的再激活，這就提出了如何防止舊的和最近的、不穩定的記憶痕跡之間的干擾的問題。理論研究表明，可以通過隨機交錯的重新激活來鞏固多個記憶，同時最大限度地減少干擾。另一種說法是，睡眠的時間微觀結構可以在特定的亞狀態下促進不同類型記憶的重新激活。
為了驗證這兩個假設，研究者開發了一種方法，可以同時記錄大海馬群，并通過瞳孔測量法監測自然睡眠小鼠的睡眠動態。振蕩的瞳孔波動揭示了以前未知的非快速眼動睡眠相關記憶過程的微觀結構。他們發現，在非快速眼動睡眠的瞳孔收縮狀態下，最近經歷的記憶重播主要發生在銳波漣漪中，而以前的記憶重播則優先發生在瞳孔擴張狀態下。
在瞳孔收縮的非快速眼動睡眠中，選擇性地中斷銳波漣漪的閉環會損害對最近記憶的回憶，而在瞳孔擴張的亞狀態中，同樣的操作對行為沒有影響。較強的外部興奮輸入是瞳孔收縮亞狀態的特征，而在瞳孔擴張亞狀態下，局部抑制的募集較高。因此，非快速眼動睡眠的微觀結構組織了記憶重放，以前的記憶和新的記憶在不同的亞狀態中被暫時分離，分別由局部和輸入驅動機制支持。研究結果表明，大腦可以在睡眠中多重處理不同的認知過程，以促進不受干擾的持續學習。
▲ Abstract：Recently acquired memories are reactivated in the hippocampus during sleep, an initial step for their consolidation. This process is concomitant with the hippocampal reactivation of previous memories, posing the problem of how to prevent interference between older and recent, initially labile, memory traces. Theoretical work has suggested that consolidating multiple memories while minimizing interference can be achieved by randomly interleaving their reactivation. An alternative is that a temporal microstructure of sleep can promote the reactivation of different types of memories during specific substates. Here, to test these two hypotheses, we developed a method to simultaneously record large hippocampal ensembles and monitor sleep dynamics through pupillometry in naturally sleeping mice. Oscillatory pupil fluctuations revealed a previously unknown microstructure of non-REM sleep-associated memory processes. We found that memory replay of recent experiences dominated in sharp-wave ripples during contracted pupil substates of non-REM sleep, whereas replay of previous memories preferentially occurred during dilated pupil substates. Selective closed-loop disruption of sharp-wave ripples during contracted pupil non-REM sleep impaired the recall of recent memories, whereas the same manipulation during dilated pupil substates had no behavioural effect. Stronger extrinsic excitatory inputs characterized the contracted pupil substate, whereas higher recruitment of local inhibition was prominent during dilated pupil substates. Thus, the microstructure of non-REM sleep organizes memory replay, with previous versus new memories being temporally segregated in different substates and supported by local and input-driven mechanisms, respectively. Our results suggest that the brain can multiplex distinct cognitive processes during sleep to facilitate continuous learning without interference.
Synaptic basis of feature selectivity in hippocampal neurons
海馬神經元特征選擇性的突觸基礎
▲ 作者：Kevin C. Gonzalez, Adrian Negrean, Zhenrui Liao, Satoshi Terada, Guofeng Zhang, Sungmoo Lee, Katalin ócsai, Balázs J. Rózsa, Michael Z. Lin, Franck Polleux & Attila Losonczy
▲ 鏈接：https://www.nature.com/articles/s41586-024-08325-9
▲ 摘要：神經科學的一個核心問題是突觸可塑性如何影響行為動物神經元的特征選擇性。海馬CA1錐體神經元通過形成被稱為位置場的空間和情境選擇性接受野，顯示出最顯著的特征選擇性形式之一，這是研究學習和記憶的突觸基礎的模型。不同形式的突觸可塑性被認為是位置場出現的細胞基質。然而，盡管經過數十年的研究，人們對突觸可塑性如何影響位置場形成和記憶編碼的理解仍然有限，這主要是由于缺乏工具和技術挑戰，無法在清醒行為動物的單神經元分辨率上可視化突觸可塑性。
為了解決這個問題，研究者開發了一種全光學方法來監測空間導航過程中單個CA1錐體神經元位置場誘導前后樹突棘的時空調諧和突觸重量變化。他們發現了一個時間上不對稱的突觸可塑性核，這是由位置場誘導周圍突觸權重的雙向修改引起的。該研究確定了基底樹突和斜樹突之間突觸可塑性的大小和時間表達的室特異性差異。研究結果提供了實驗證據，證明突觸可塑性與海馬神經元空間選擇性的快速出現有關，而空間選擇性是情景記憶的關鍵先決條件。
▲ Abstract：A central question in neuroscience is how synaptic plasticity shapes the feature selectivity of neurons in behaving animals1. Hippocampal CA1 pyramidal neurons display one of the most striking forms of feature selectivity by forming spatially and contextually selective receptive fields called place fields, which serve as a model for studying the synaptic basis of learning and memory. Various forms of synaptic plasticity have been proposed as cellular substrates for the emergence of place fields. However, despite decades of work, our understanding of how synaptic plasticity underlies place-field formation and memory encoding remains limited, largely due to a shortage of tools and technical challenges associated with the visualization of synaptic plasticity at the single-neuron resolution in awake behaving animals. To address this, we developed an all-optical approach to monitor the spatiotemporal tuning and synaptic weight changes of dendritic spines before and after the induction of a place field in single CA1 pyramidal neurons during spatial navigation. We identified a temporally asymmetric synaptic plasticity kernel resulting from bidirectional modifications of synaptic weights around the induction of a place field. Our work identified compartment-specific differences in the magnitude and temporal expression of synaptic plasticity between basal dendrites and oblique dendrites. Our results provide experimental evidence linking synaptic plasticity to the rapid emergence of spatial selectivity in hippocampal neurons, a critical prerequisite for episodic memory.
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