Nature, 30 January 2025, Volume 637, Issue 8048

《自然》2025年1月30日，第637卷，8048期

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物理学Physics

Ultrabroadband integrated electro-optic frequency comb in lithium tantalate

钽酸锂中超宽带集成电光频率梳

▲ 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

▲ 链接：https://www.nature.com/articles/s41586-024-08354-4

▲ 摘要：基于Kerr参数振荡的集成频率梳发生器已经产生了芯片级、千兆赫间隔的梳，具有跨超大规模电信、低噪声微波合成、光探测和测距以及天体物理光谱仪校准的新应用。铌酸锂（LiNbO₃）光子集成电路（PICs）的最新进展推动了芯片规模的电光（EO）频率梳，提供精确的梳线定位和简单的操作，而不依赖于形成耗散克尔孤子。然而，由于驱动非谐振电容电极所需的微波功率大，以及LiNbO₃的强固有双折射，目前集成EO梳子的光谱覆盖范围有限。

研究者通过集成三重谐振结构克服了这两个挑战，将单片微波集成电路与基于最近出现的薄膜LiTaO₃的PICs相结合。与传统的非谐振微波设计相比，通过共振增强的EO相互作用和减少的双折射，研究实现了4倍的梳子跨度扩展和16倍的功率降低。在混合集成激光二极管的驱动下，梳子的跨度超过450纳米（超过60太赫兹），有2000多条线，而发生器的占地面积仅为1平方厘米。

此外，研究者还观察到强EO耦合导致梳子存在范围增加，接近光学微谐振器的全自由光谱范围。超宽带梳状发生器与失谐不确定操作相结合，可以推进芯片级光谱分析和超低噪声毫米波合成，并解锁八度跨度的EO梳状器。微波和光子协同设计的方法可以扩展到广泛的集成光电应用。

▲ 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

扭曲石墨烯中摩尔驱动的拓扑电子晶体

▲ 作者：Ruiheng Su, Dacen Waters, Boran Zhou, Kenji Watanabe, Takashi Taniguchi, Ya-Hui Zhang, Matthew Yankowitz & Joshua Folk

▲ 链接：https://www.nature.com/articles/s41586-024-08239-6

▲摘要：在稀薄的二维电子气体中，库仑相互作用可以稳定维格纳晶体的形成。虽然维格纳晶体在拓扑上是微不足道的，但据预测，部分填充带中的电子可以自发地打破连续的平移对称性和时间反转对称性，从而产生一种被称为反常霍尔晶体的拓扑电子晶体。

研究者报告了扭曲的双层—三层石墨烯中异常霍尔晶体的广义版本的特征，其形成是由莫尔阱势驱动的。晶体形成于每4个摩尔粒子（ν=1/4）有1个电子的带填充，使单位细胞面积增加了4倍，与整数量子反常霍尔效应相一致。

态的陈数是特别可调的，它可以在电场和磁场的作用下在+1和-1之间可逆地切换。其他几个拓扑电子晶体出现在适度的磁场中，起源于ν=1/3,1/2,2/3和3/2。相互作用修饰能带的量子几何可能与原始母能带的量子几何非常不同，这使得可能在未来发现相关驱动的拓扑现象。

▲ 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

具有点费米表面的半金属Weyl铁磁体的合成

▲ 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

▲ 链接：https://www.nature.com/articles/s41586-024-08330-y

▲ 摘要：由新兴的拓扑费米子控制的量子材料已经成为物理学的基石。石墨烯中的狄拉克费米子构成了摩尔量子物质的基础，磁拓扑绝缘体中的狄拉克费米子使得量子反常霍尔效应（QAH）的发现成为可能。相比之下，很少有材料的电磁响应是由涌现的Weyl费米子主导的。几乎所有已知的Weyl材料绝大多数都是金属，并且在很大程度上由无关的常规电子控制。

这项研究从理论上预测并在实验上观察了范德华（Cr,Bi）₂Te₃中的半金属Weyl铁磁体。在输运中，他们发现了一个大于0.5的记录体异常霍尔角以及非金属电导率，这是一个与传统铁磁体截然不同的制度。结合对称性分析，研究数据表明一个由两个Weyl点组成的半金属费米表面，具有超过体布里渊区线性尺寸75%的巨大分离，并且没有其他电子态。

研究者使用最先进的晶体合成技术，广泛调整电子结构，使其能够湮灭Weyl状态，并可视化一个独特的拓扑相图，显示广泛的陈氏绝缘，Weyl半金属和磁性半导体区域。研究者表示，对半金属Weyl铁磁体的观察为研究新的相关态和非线性现象以及零磁场Weyl自旋电子和光学器件提供了一条途径。

▲ 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

通过反极性挫折增强反铁电体的能量存储

▲ 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

▲ 链接：https://www.nature.com/articles/s41586-024-08505-7

▲摘要：介质储能电容器充放电速度快、可靠性高，在尖端电子电气设备中发挥着重要作用。为了追求电容器的小型化和集成化，电介质必须提供高能量密度和效率。具有反平行偶极子结构的反铁电体由于其在场致铁电态中可忽略的剩余极化和高的最大极化而在高性能能量存储中具有重要的意义。然而，低反铁电—铁电相变场和伴随的大磁滞损耗会降低能量密度和可靠性。

在相场模拟的指导下，研究者提出了一种新的策略，通过加入非极性或极性成分来挫败反铁电体中的反极性有序。实验表明，该方法有效地调节了反铁电—铁电相变场，同时减小了磁滞损耗。在基于PbZrO₃的薄膜中，他们在5.51 MV cm^?1的电场下实现了189 J cm^?3的反铁电体中创纪录的高能量密度以及81%的高效率，可与最先进的储能介质相媲美。扫描透射电子显微镜的原子尺度表征直接揭示了分散的非极性区阻碍了远程反极性有序，有助于提高性能。这种策略为操纵极化分布和提高反铁电体的储能性能提供了新的机会。

▲ 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 PbZrO_3-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.

化学Chemistry

Durable all-inorganic perovskite tandem photovoltaics

耐用的全无机钙钛矿串联光伏电池

▲ 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

▲ 链接：https://www.nature.com/articles/s41586-024-08432-7

▲ 摘要：用无机阳离子（如Cs+）取代有机阳离子（如甲基铵和甲脒）制备全无机钙钛矿是提高钙钛矿太阳能电池（PSCs）长期光稳定性和热稳定性的有效概念。因此，无机钙钛矿串联太阳能电池（IPTSCs）是打破效率瓶颈和解决稳定性问题的有希望的候选者。然而，由于锡离子诱导的较差的薄膜形成和深阱状态，在制备双端（2T）IPTSC方面仍然存在挑战。

研究者采用对甲苯磺酰肼（PTSH）的配体进化（LE）策略来调节无机窄带隙（NBG）钙钛矿中的薄膜形成并消除深层陷阱，从而成功开发了2T IPTSC。IPTSC在最大功率点跟踪下具有卓越的耐用性，在65°C和85°C下分别保持80%的初始效率1510小时和800小时。研究阐明了LE有意利用无机NBG钙钛矿生长的多种作用，有望为开发高效稳定的IPTSC提供有洞察力的指导。

▲ 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.

生物学Biology

Sleep microstructure organizes memory replay

睡眠微观结构组织记忆重放

▲ 作者：Hongyu Chang, Wenbo Tang, Annabella M. Wulf, Thokozile Nyasulu, Madison E. Wolf, Antonio Fernandez-Ruiz & Azahara Oliva

▲ 链接：https://www.nature.com/articles/s41586-024-08340-w

▲摘要：最近获得的记忆在睡眠时在海马体中被重新激活，这是巩固记忆的第一步。这一过程伴随着海马体对先前记忆的再激活，这就提出了如何防止旧的和最近的、不稳定的记忆痕迹之间的干扰的问题。理论研究表明，可以通过随机交错的重新激活来巩固多个记忆，同时最大限度地减少干扰。另一种说法是，睡眠的时间微观结构可以在特定的亚状态下促进不同类型记忆的重新激活。

为了验证这两个假设，研究者开发了一种方法，可以同时记录大海马群，并通过瞳孔测量法监测自然睡眠小鼠的睡眠动态。振荡的瞳孔波动揭示了以前未知的非快速眼动睡眠相关记忆过程的微观结构。他们发现，在非快速眼动睡眠的瞳孔收缩状态下，最近经历的记忆重播主要发生在锐波涟漪中，而以前的记忆重播则优先发生在瞳孔扩张状态下。

在瞳孔收缩的非快速眼动睡眠中，选择性地中断锐波涟漪的闭环会损害对最近记忆的回忆，而在瞳孔扩张的亚状态中，同样的操作对行为没有影响。较强的外部兴奋输入是瞳孔收缩亚状态的特征，而在瞳孔扩张亚状态下，局部抑制的募集较高。因此，非快速眼动睡眠的微观结构组织了记忆重放，以前的记忆和新的记忆在不同的亚状态中被暂时分离，分别由局部和输入驱动机制支持。研究结果表明，大脑可以在睡眠中多重处理不同的认知过程，以促进不受干扰的持续学习。

▲ 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

海马神经元特征选择性的突触基础

▲ 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

▲ 链接：https://www.nature.com/articles/s41586-024-08325-9

▲ 摘要：神经科学的一个核心问题是突触可塑性如何影响行为动物神经元的特征选择性。海马CA1锥体神经元通过形成被称为位置场的空间和情境选择性接受野，显示出最显著的特征选择性形式之一，这是研究学习和记忆的突触基础的模型。不同形式的突触可塑性被认为是位置场出现的细胞基质。然而，尽管经过数十年的研究，人们对突触可塑性如何影响位置场形成和记忆编码的理解仍然有限，这主要是由于缺乏工具和技术挑战，无法在清醒行为动物的单神经元分辨率上可视化突触可塑性。

为了解决这个问题，研究者开发了一种全光学方法来监测空间导航过程中单个CA1锥体神经元位置场诱导前后树突棘的时空调谐和突触重量变化。他们发现了一个时间上不对称的突触可塑性核，这是由位置场诱导周围突触权重的双向修改引起的。该研究确定了基底树突和斜树突之间突触可塑性的大小和时间表达的室特异性差异。研究结果提供了实验证据，证明突触可塑性与海马神经元空间选择性的快速出现有关，而空间选择性是情景记忆的关键先决条件。

▲ 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.