翻译 | 冯维维

Science, 16 AUGUST 2019, VOL 365, ISSUE6454

《科学》2019年8月16日，第365卷6454期

材料学Material Sciences

Thermal unequilibrium of strained black CsPbI₃thin films

钙钛矿CsPbI₃黑色相的热不均衡性

作者：Julian A. Steele, Handong Jin, Iurii Dovgaliuk, Johan Hofkens, Maarten B. J. Roeffaers, etc.

链接：

https://science.sciencemag.org/content/365/6454/679

摘要：

高温全无机钙钛矿CsPbI₃黑色相在室温下相对于黄色非钙钛矿相是亚稳态的。由于只有黑相具有旋光性，这就阻碍了CsPbI₃在光电器件中的应用。

作者报道了利用衬底夹紧和双轴应变使黑相CsPbI₃薄膜在室温下保持稳定。作者采用同步色散、掠入射、广角x射线散射等方法，跟踪了黑色CsPbI₃薄膜在330℃退火后冷却时，晶体畸变的引入和应变驱动织构的形成。

应变界面大大提高了黑色CsPbI₃薄膜的热稳定性，并通过热力学从头算模型进行了验证。

Abstract

The high-temperature, all-inorganic CsPbI₃perovskite black phase is metastable relative to its yellow, nonperovskite phase at room temperature. Because onlythe black phase is optically active, this represents an impediment for the use of CsPbI₃in optoelectronic devices. We report the use of substrate clamping and biaxial strain to render black-phase CsPbI₃thin films stable at room temperature. We used synchrotron-based, grazing incidence, wide-angle x-ray scattering to track the introduction of crystal distortions and strain-driventexture formation within black CsPbI₃thin films when they were cooled after annealing at 330°C. The thermal stability of black CsPbI₃thin films is vastly improved by the strained interface, a response verified by ab initio thermodynamic modeling.

Nearly ferromagnetic spin-triplet superconductivity

不同寻常的超导体：近铁磁自旋三重态超导性

作者：Sheng Ran, Chris Eckberg, Qing-Ping Ding, Yuji Furukawa, Nicholas P. Butch, etc.

链接：

https://science.sciencemag.org/content/365/6454/684

摘要：

在传统超导体和许多非传统超导体中，形成库珀对的电子呈现出指向相反方向的自旋。

一个外加磁场可以通过让这两个自旋朝向同一方向，轻易地“打破”这样的库珀对，并破坏超导性。相比之下，自旋三重态超导体对磁场的弹性要大得多。但这种候选材料很少被发现。

研究者通过观察 UTe₂材料中自旋三重态超导性（包括一个非常大的各向异性的上临界磁场）的特征，给这种材料中增加了一种新选择。由于自旋三重态超导体可能会自然地表现出拓扑超导性，这种材料可能会让量子计算感兴趣。

Abstract

Inconventional, and in many unconventional, superconductors, the electrons that form Cooper pairs have spins pointing in opposite directions. An applied magnetic field can easily “break”such pairs—and destroy superconductivity—by aligning both spins in the same direction. In contrast, spin-triplet superconductors are much more resilient to magnetic fields. Very few candidates for such materials have been discovered. Ran et al. add to this select group by observing signatures of spin-triplet superconductivity, including a very large and anisotropic upper critical magnetic field, in the material UTe₂. Because spin-triplet superconductors may naturally exhibit topological superconductivity, this material may also be of interest in quantum computing.

Stabilizing heterostructures of soft perovskite semiconductors

稳定软钙钛矿半导体的异质结构

作者：Yanbo Wang, Tianhao Wu, Julien Barbaud, Weiyu Kong, Xudong Yang, Liyuan Han

链接：

https://science.sciencemag.org/content/365/6454/687

摘要：

太阳能电池中使用的杂化钙钛矿晶格中的弱键能促进表面分解，并干扰电荷载流子层形成稳定的异质结构。

研究者指出，在含铅表面和氯化石墨烯氧化层的薄膜中，铅与氯和氧原子之间形成了强键。

该界面与普通的空穴输送材料一起被用于制造太阳能电池，在60℃运行1000小时后，该电池仍保持了其21%初始效率的90%。

Abstract

The weak bonding in the crystal lattice of hybrid perovskites used in solar cells promotes surface decomposition and interferes with the formation of stable heterostructures with the charge carrier layers. Y. Wang et al. show that strong bonds are formed between lead and both chlorine and oxygen atoms in a film with a lead-rich surface and a chlorinated graphene oxide layer. This interface was used with common hole-transporting materials to fabricate solar cells that maintained 90% of their initial efficiency of 21% after operation at 60°C for 1000 hours.

物理学Physics

Switching on quantum dot lasers

打开量子点激光器

作者：Oleg V. Kozlov, Young-Shin Park, Jeongkyun Roh, Igor Fedin, Tom Nakotte, Victor I. Klimov

链接：

https://science.sciencemag.org/content/365/6454/672

摘要：

胶体半导体量子点（QD）是实现高柔性、可溶解处理的光学增益介质的理想材料，但由于非辐射螺旋复合限制了极短的光学增益寿命，因此很难用于激光激射。

通过将QD内部用于阻止螺旋衰减的成分分级，与用于抑制寄生基态吸收的合成后充电相结合，作者将激光阈值降低到低于单点激子限制的值。

与传统的基于多激子的激光方案不同，这一新方法能够促进可溶解处理的激光器件的发展，从而有助于将激光技术扩展到传统外延生长半导体材料无法触及的领域。

Abstract

Colloidal semiconductor quantum dots (QDs) are attractive materials for realizing highly flexible, solution-processable optical gain media, but they are difficult to use in lasing because of complications associated with extremely short optical-gain lifetimes limited by nonradiative Auger recombination. By combining compositional grading of the QD's interior for hindering Auger decay with post synthetic charging for suppressing parasitic ground-state absorption, we can reduce the lasing threshold to values below the single-exciton-per-dot limit. As a favorable departure from traditional multi-exciton–based lasing schemes, our approach should facilitate the development of solution-processable lasing devices and thereby help to extend the reach of lasing technologies into areas not accessible with traditional, epitaxially grown semiconductor materials.

Quantum-state–selective electron recombination studies suggest enhanced abundance of primordial HeH⁺

量子态选择性电子重组研究表明原始氦氢化物离子丰度增加

作者：Old?ich Novotny, Patrick Wilhelm, Daniel Paul, ábel Kálosi, Andreas Wolf, etc.

链接：

https://science.sciencemag.org/content/365/6454/676

摘要：

早期宇宙中第一颗恒星的形成时期主要由简单的原子和分子组成，主要是由氢和氦两种元素组成。

作者用一个低温离子存储环结合一个合并的电子束测量离解复合的状态比速率系数，这是一个电子破坏分子离子的过程。他们发现氦氢化物离子（HeH⁺）最低旋转态的电子复合速率与之前在室温下的测量结果相比有明显的下降。

在第一个恒星和星系形成的红移过程中，冷态HeH⁺的破坏减少，转化为这种原始分子的丰度增加。

Abstract

The epoch of first star formation in the early Universe was dominated by simple atomic and molecular species consisting mainly of two elements: hydrogen and helium. We used a cryogenic ion storage ring combined with a merged electron beam to measure state-specific rate coefficients of dissociative recombination, a process by which electrons destroy molecular ions. We found a pronounced decrease of the electron recombination rates for the lowest rotational states of the helium hydride ion (HeH⁺), compared with previous measurements at room temperature. The reduced destruction of cold HeH⁺translates into an enhanced abundance of this primordial molecule at redshifts of first star and galaxy formation.

作物Crops

Teosinte liguleallele narrows plant architecture and enhances high-density maize yields

等位基因让高密度玉米种植“更瘦身”更高产

作者：Jinge Tian, Chenglong Wang, Jinliang Xia, Feng Tian, etc.

链接：

https://science.sciencemag.org/content/365/6454/658

摘要：

为了满足日益增长的粮食需求，现代农业的种植密度越来越大。

作者在玉米的野生祖先teosinte中发现了一种基因，并利用它来改变玉米，使这种植物株型“更瘦”，尽管如此，其叶子还是可以接触到阳光。

只有在现代农业高密度种植的特点下，这种产量优势才会变得明显，这或许可以解释为什么在过去几千年的玉米驯化过程中，这种基因没有被纳入作物的行列。

Abstract

To meet increasing demands for food, modern agriculture works with increasingly dense plantings. Tian et al. identified a gene in teosinte, the wild ancestorof maize, and used it to alter maize such that the plant has a narrower architecture that nonetheless allows leaves access to sunlight. The yield advantage only becomes evident with the high-density plantings characteristic of modern agriculture, perhaps explaining why this gene was not brought into the fold during the previous millennia of maize domestication.

地质学Geology

Primordial and recycled helium isotope signatures in the mantle transition zone

“钻石”窗户透视地幔深处

作者：S Timmerman, M. Honda, A. D. Burnham, Y. Amelin, S. Woodland, E. Tohver, etc.

链接：

https://science.sciencemag.org/content/365/6454/692

摘要：

氦同位素为人们打开了一扇窗，使人们得以窥见地球庞大的地幔中最深、最古老的部分。然而，有几个过程往往会掩盖地表爆发的玄武岩熔岩储层中氦同位素的信号。

作者发现了一组在地球深处形成并迅速喷发的钻石，而且它们避免了近地表污染。他们发现了深部原始岩石来源的证据，以及来自旧俯冲板块的混合沉积物。

作者表示，从这些钻石中提取的特征对建设地球化学和动力学模型有一定意义。

Abstract

Heliumisotopes provide a window into the very deepest and oldest parts of Earth's voluminous mantle. However, several processes tend to obscure the heliumisotope signal from reservoirs in basaltic lavas that have erupted at the surface. Timmerman et al. identified a set of diamonds that formed deep within Earth and were rapidly erupted, which have avoided near-surface contamination.They find evidence for a deep, primordial rock source along with mixing of sediments from old subducting plates. The signatures extracted from the sediamonds have implications for chemical and dynamic models of Earth.

天体物理Astrophysics

Relativistic redshift of the star S0-2 orbiting the Galactic Center supermassive black hole

银河系中心的引力红移

作者：Tuan Do, Aurelien Hees, Andrea Ghez, Gregory D. Martinez, Devin S. Chu, etc.

链接：

http://fanyi.youdao.com/?keyfrom=fanyi.logo

摘要：

广义相对论预测，一个物体在强引力场（例如靠近黑洞）中发出的光会被转移到更长的波长。这种引力红移在牛顿引力理论中并不存在。

作者监测了恒星S0-2经过人马座A*时的位置和光谱，人马座A*是银河系中心的超大质量黑洞。在距离S0-2 16年轨道最近的地方，他们探测到了引力红移对其光谱的影响。

这些结果在5σ水平比牛顿引力更符合广义相对论。

Abstract

General relativity predicts that light emitted by an object in a strong gravitational field—for example, close to a black hole—should be shifted to longer wavelengths. This gravitational redshift does not exist in the Newtonian theory of gravity. Do et al. monitored the position and spectrum of the star S0-2 as it passed Sagittarius A*, the supermassive black hole at the center of the Milky Way. Around the closest part of S0-2's 16-year orbit, they detected the effect of gravitational redshift on its spectrum. These results are more consistent with general relativity than Newtonian gravity at the 5σ level.

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