自然科学经典导论电子书（自然20220623出版一周论文导读）

编译 | 冯维维

Nature, 23 June 2022，Volume 606 Issue 7915

《自然》2022年6月23日，第606卷，7915期

物理学Physics

Solar flare accelerates nearly all electrons in a large coronal volume

太阳耀斑加速一个大日冕体中几乎所有电子

▲ 作者：Gregory D. Fleishman, Gelu M. Nita, Bin Chen, Sijie Yu & Dale E. Gary

▲ 链接：

https://www.nature.com/articles/s41586-022-04728-8

▲ 摘要：

太阳耀斑是由日冕中自由磁能的迅速释放驱动的，它能将相当一部分（10%或更多）可用电子加速到高能。由高能电子在耀斑中加速产生的硬X射线需要较高的环境密度来探测。这就把观察到的体积限制在更密集的区域，这些区域不一定要对整个加速电子的体积进行采样。

作者报告了来自微波观测的太阳耀斑中演化的空间分辨分布的热和非热电子，结果显示了加速度区域的真实范围。这些分布显示，当热等离子体耗尽时，只有（或几乎只有）非热电子填充的体积，这意味着所有电子在那里都经历了显著的加速。这个体积与周围环境——更典型的耀斑等离子体隔绝，主要是热粒子，非热电子的比例较小。这种高效率的加速在释放自由磁能的同一体积内发生。

▲ Abstract：

Solar flares, driven by prompt release of free magnetic energy in the solar corona, are known to accelerate a substantial portion (ten per cent or more) of available electrons to high energies. Hard X-rays, produced by high-energy electrons accelerated in the flare, require a high ambient density for their detection. This restricts the observed volume to denser regions that do not necessarily sample the entire volume of accelerated electrons. Here we report evolving spatially resolved distributions of thermal and non-thermal electrons in a solar flare derived from microwave observations that show the true extent of the acceleration region. These distributions show a volume filled with only （or almost only） non-thermal electrons while being depleted of the thermal plasma, implying that all electrons have experienced a prominent acceleration there. This volume is isolated from a surrounding, more typical flare plasma of mainly thermal particles with a smaller proportion of non-thermal electrons. This highly efficient acceleration happens in the same volume in which the free magnetic energy is being released.

Observation of a correlated free four-neutron system

相关自由四中子系统的观测

▲ 作者：M. Duer, T. Aumann, M. V. Zhukov Show authors

▲ 链接：

https://www.nature.com/articles/s41586-022-04827-6

▲ 摘要：

核物理学界一个长期存在的问题是，无电荷核系统是否存在。只有中子星代表着接近纯粹的中子系统，那里的中子被引力挤压在一起，密度非常高。几十年来，对孤立的多中子系统的实验研究一直是一项持续不断的探索，其中特别关注四中子系统，结果到目前为止，只有少数迹象表明它的存在，使得四中子系统在60年里一直是一个难以捉摸的核系统。

作者报道了在四中子系统阈值附近观测到的类共振结构，该结构与短时间内存在的准束缚四中子态相一致。这种状态的能量和宽度为人们理解核力提供了一个关键的基准。利用放射性高能8He束在大动量转移中进行敲除反应的实验方法是关键。

▲ Abstract：

A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades, with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far, leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy 8He beam was key.

Continuous Bose–Einstein condensation

连续的玻色-爱因斯坦凝聚

▲ 作者：Chia Chen, Rodrigo González Escudero, Jiří Minář, Benjamin Pasquiou, Shayne Bennetts & Florian Schreck

▲ 链接：

https://www.nature.com/articles/s41586-022-04731-z

▲ 摘要：

玻色-爱因斯坦凝聚体（BECs）是一种宏观相干物质波，它彻底改变了量子科学和原子物理学。它们对量子模拟和传感很重要，例如，空间原子干涉仪和爱因斯坦等效原理的雄心勃勃的测试。长期以来，量子气体设备的一个限制是需要按时间顺序执行冷却阶段，这限制了这些设备的脉冲操作。

作者通过创造一个连续波（CW）的锶原子无限持续凝聚，来证明连续的玻色-爱因斯坦凝聚。相干物质波是通过从热浴中获得的玻色激发原子增益来进行放大的。通过稳定地补充这个浴槽，同时达到比以往工作高1000倍的相空间密度，保持冷凝的条件。该实验是用全反射腔镜模拟连续波光学激光器的物质波。这个原理证明的演示提供了迄今为止原子光学中缺失的一个新部分，实现了连续相干物质波器件的构建。

▲ Abstract：

Bose–Einstein condensates (BECs) are macroscopic coherent matter waves that have revolutionized quantum science and atomic physics. They are important to quantum simulation and sensing, for example, underlying atom interferometers in space4 and ambitious tests of Einstein’s equivalence principle5,6. A long-standing constraint for quantum gas devices has been the need to execute cooling stages time-sequentially, restricting these devices to pulsed operation. Here we demonstrate continuous Bose–Einstein condensation by creating a continuous-wave (CW) condensate of strontium atoms that lasts indefinitely. The coherent matter wave is sustained by amplification through Bose-stimulated gain of atoms from a thermal bath. By steadily replenishing this bath while achieving 1,000 times higher phase-space densities than previous works, we maintain the conditions for condensation. Our experiment is the matter wave analogue of a CW optical laser with fully reflective cavity mirrors. This proof-of-principle demonstration provides a new, hitherto missing piece of atom optics, enabling the construction of continuous coherent-matter-wave devices.

Many-body theory of positron binding to polyatomic molecules

正电子与多原子分子结合的多体理论

▲ 作者：Jaroslav Hofierka, Brian Cunningham, Charlie M. Rawlins, Charles H. Patterson & Dermot G. Green

▲ 链接：

https://www.nature.com/articles/s41586-022-04703-3

▲ 摘要：

正电子与分子的结合是增强正电子湮灭和正电子分子光谱的关键。虽然已经测量了约90个多原子分子的正电子结合能，但其精确从头算理论描述仍然难以捉摸。在实验研究的分子中，从头计算方式只存在六种；这些计算与极性分子的实验一致，精确度最高只有25%，且未能预测非极性分子的结合。理论上的挑战来自于需要精确描述强多体相关性，包括电子云的极化、电子-正电子库仑相互作用的筛选以及虚拟-正电子形成的独特过程。

作者开发了一个正电子-分子相互作用的多体理论，该理论与实验取得了极好的一致性，并预测了甲酰胺和碱基的结合。该框架定量地捕捉了多体相关性的作用，并显示了它们在增强极性分子结合、使非极性分子结合以及将湮灭率提高2至3个数量级方面的关键作用。该多体方法可以扩展到分子和凝聚态中的正电子散射和湮灭γ射线能谱，为改善材料科学诊断、开发基于反物质的技术（包括正电子陷阱、电子束和正电子发射断层扫描）和了解星系中的正电子提供基本的洞察力和预测能力。

▲ Abstract：

Positron binding to molecules is key to extremely enhanced positron annihilation and positron-based molecular spectroscopy1. Although positron binding energies have been measured for about 90 polyatomic molecules1,2,3,4,5,6, an accurate ab initio theoretical description of positron–molecule binding has remained elusive. Of the molecules studied experimentally, ab initio calculations exist for only six; these calculations agree with experiments on polar molecules to at best 25 per cent accuracy and fail to predict binding in nonpolar molecules. The theoretical challenge stems from the need to accurately describe the strong many-body correlations including polarization of the electron cloud, screening of the electron–positron Coulomb interaction and the unique process of virtual-positronium formation (in which a molecular electron temporarily tunnels to the positron)1. Here we develop a many-body theory of positron–molecule interactions that achieves excellent agreement with experiment (to within 1 per cent in cases) and predicts binding in formamide and nucleobases. Our framework quantitatively captures the role of many-body correlations and shows their crucial effect on enhancing binding in polar molecules, enabling binding in nonpolar molecules, and increasing annihilation rates by 2 to 3 orders of magnitude. Our many-body approach can be extended to positron scattering and annihilation γ-ray spectra in molecules and condensed matter, to provide the fundamental insight and predictive capability required to improve materials science diagnostics, develop antimatter-based technologies (including positron traps, beams and positron emission tomography), and understand positrons in the Galaxy.

Engineering topological states in atom-based semiconductor quantum dots

原子基半导体量子点的工程拓扑态

▲ 作者：M. Kiczynski, S. K. Gorman, H. Geng, M. B. Donnelly, Y. Chung, Y. He, J. G. Keizer & M. Y. Simmons

▲ 链接：

https://www.nature.com/articles/s41586-022-04706-0

▲ 摘要：

通过量子模拟实现可控费米子量子系统有助于探索凝聚态物理中许多最有趣的效应。半导体量子点在量子模拟方面特别有前途，它们可以被设计成具有很强的量子相关性。然而，尽管Fermi-Hubbard模型和Nagaoka铁磁的模拟已被报道过，最简单的一维强相关拓扑物质模型，即Su- schrieffer - heeger（SSH）多体模型，迄今为止仍然难以实现，主要是由于精确设计电子之间的远程相互作用来重现所选的哈密顿量的挑战。

作者展示了在强库仑约束的硅中精确放置原子，可以设计至少6个全外延平面内门来调整10个量子点线性阵列的能级，以实现多体SSH模型的普通相和拓扑相。强大的现场能量（约25毫伏）和在独特的交错设计中以亚纳米精度设计门的能力，可以调整细胞间和细胞内电子传输的比例，以观察在四分之一填充有两个电导峰的拓扑相的清晰特征，而与之相比，trivial相有十个电导峰。作者通过在一个与量子位同构的费米系统中演示SSH模型，展示了其高度可控的量子系统，以及它对未来强相互作用电子的模拟的有用性。

▲ Abstract：

The realization of controllable fermionic quantum systems via quantum simulation is instrumental for exploring many of the most intriguing effects in condensed-matter physics. Semiconductor quantum dots are particularly promising for quantum simulation as they can be engineered to achieve strong quantum correlations. However, although simulation of the Fermi–Hubbard model and Nagaoka ferromagnetism have been reported before, the simplest one-dimensional model of strongly correlated topological matter, the many-body Su–Schrieffer–Heeger (SSH) model, has so far remained elusive—mostly owing to the challenge of precisely engineering long-range interactions between electrons to reproduce the chosen Hamiltonian. Here we show that for precision-placed atoms in silicon with strong Coulomb confinement, we can engineer a minimum of six all-epitaxial in-plane gates to tune the energy levels across a linear array of ten quantum dots to realize both the trivial and the topological phases of the many-body SSH model. The strong on-site energies (about 25 millielectronvolts) and the ability to engineer gates with subnanometre precision in a unique staggered design allow us to tune the ratio between intercell and intracell electron transport to observe clear signatures of a topological phase with two conductance peaks at quarter-filling, compared with the ten conductance peaks of the trivial phase. The demonstration of the SSH model in a fermionic system isomorphic to qubits showcases our highly controllable quantum system and its usefulness for future simulations of strongly interacting electrons.

化学Chemistry

Organic bipolar transistors

有机双极晶体管

▲ 作者：Shu-Jen Wang, Michael Sawatzki, Ghader Darbandy, Felix Talnack, Jörn Vahland, Marc Malfois, Alexander Kloes, Stefan Mannsfeld, Hans Kleemann & Karl Leo

▲ 链接：

https://www.nature.com/articles/s41586-022-04837-4

▲ 摘要：

利用薄膜半导体制造的器件由于新的应用可能性引起人们广泛关注。在适用于薄膜电子的材料系统中，有机半导体尤其令人感兴趣。它们的低成本、生物相容性碳基材料和通过蒸发或印刷等简单技术的沉积，使有机半导体器件能够用于无处不在的电子产品，如那些用于人体或衣服和包装上的器件。只有有机晶体管的性能得到显著提高，有机电子的潜力才能得到充分利用。

作者展示了器件性能优异的有机双极晶体管：此前描述的垂直结构和高晶体有机rubrene薄膜产生的器件具有高差分放大（超过100）和优于常规器件的高频性能。这些双极晶体管还提供了了解少数载流子扩散长度——有机半导体的一个关键参数。该研究结果为高性能有机电子器件的新概念打开了大门，具有更快的切换速度。

▲ Abstract：

Devices made using thin-film semiconductors have attracted much interest recently owing to new application possibilities. Among materials systems suitable for thin-film electronics, organic semiconductors are of particular interest; their low cost, biocompatible carbon-based materials and deposition by simple techniques such as evaporation or printing enable organic semiconductor devices to be used for ubiquitous electronics, such as those used on or in the human body or on clothing and packages. The potential of organic electronics can be leveraged only if the performance of organic transistors is improved markedly. Here we present organic bipolar transistors with outstanding device performance: a previously undescribed vertical architecture and highly crystalline organic rubrene thin films yield devices with high differential amplification (more than 100) and superior high-frequency performance over conventional devices. These bipolar transistors also give insight into the minority carrier diffusion length—a key parameter in organic semiconductors. Our results open the door to new device concepts of high-performance organic electronics with ever faster switching speeds.

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