《自然》（20210408出版）一周论文导读

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编译 | 李言

Nature , 8 April 2021, Volume 592 Issue 7853

《自然》 2021年4月8日，第592卷，7853期

天文学 Astronomy

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

在炎热巨型行星大气层中的五种含碳和氮的物质

作者：Paolo Giacobbe, Matteo Brogi, Siddharth Gandhi, Patricio E. Cubillos, et al.

链接：

https://www.nature.com/articles/s41586-021-03381-x

摘要

先前对热木星的观测表明，它们在其主星前面经过时大气层中经常存在水蒸气和一氧化碳；这已经通过在通常的化学平衡假设下根据太阳的比例组成进行了研究。

氰化氢和这两种分子都在HD 209458b的大气中被发现。HD 209458b是一个被充分研究过的热木星（平衡温度在1500 k左右），曾经检测出氨，但随后被否认。

在此，我们报告HD 209458b的观察结果，显示存在水、一氧化碳、氰化氢、甲烷、氨和乙炔，每个分子5.3到9.9个标准偏差。辐射和化学平衡的大气模型表明，探测到的物质具有富碳化学成分，碳氧比接近或大于1，高于太阳的值（0.55）。

根据现有的关于大气化学与行星形成和迁移情景的模型，这可能表明HD 209458b在远离目前位置的地方形成，随后向内迁移。

Abstract

Previous observations of hot Jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour and carbon monoxide in their atmospheres; this has been studied in terms of scaled solar composition under the usual assumption of chemical equilibrium. Both molecules as well as hydrogen cyanide were found in the atmosphere of HD 209458b, a well studied hot Jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there and subsequently refuted. Here we report observations of HD 209458b that indicate the presence of water ( H2 O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (C H4 ), ammonia (N H3 ) and acetylene ( C2H2 ), with statistical significance of 5.3 to 9.9 standard deviations per molecule. Atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). According to existing models relating the atmospheric chemistry to planet formation and migration scenarios, this would suggest that HD 209458b formed far from its present location and subsequently migrated inwards.

考古学 Archaeology

Innovative Homo sapiens behaviours 105,000 years ago in a wetter Kalahari

发生在105000年前卡拉哈里盆地中的人类创新行为

作者：Jayne Wilkins, Benjamin J. Schoville, Robyn Pickering, Luke Gliganic, et al.

链接：

https://www.nature.com/articles/s41586-021-03419-0

摘要

非洲的考古记录为智人复杂的符号和技术行为的出现提供了最早的证据。然而，保存完好、年代学较强的晚更新世地层遗址在南非内陆非常罕见，因此海岸假说仍未得到验证。

在此，我们展示了与大约10.5万年前南部非洲沿海地区的人类发明相似的早期人类发明，他们大约在同一时期生活在600多公里外的内陆地区。我们报告了有意收集非实用物体（方解石晶体）和鸵鸟蛋壳的证据。

这些证据来自对于卡拉哈里盆地南部的一个层状岩石矿床的挖掘现场，我们通过光释光测年技术确定其距今约10.5万年。残存凝灰岩矿床的铀钍定年法表明，这里偶尔会有大量淡水流动；这些岩层中最古老的可以追溯到11至10万年之间，与考古发现相一致。

我们的结果表明，南部非洲内陆人类的创新行为并不落后于靠近海岸的人群，而且这些创新行为可能是在潮湿的大草原环境中发展起来的。

Abstract

The archaeological record of Africa provides the earliest evidence for the emergence of the complex symbolic and technological behaviours that characterize Homo sapiens. However, stratified Late Pleistocene sites with good preservation and robust chronologies are rare in the interior of southern Africa, and the coastal hypothesis therefore remains untested. Here we show that early human innovations that are similar to those dated to around 105 thousand years ago (ka) in coastal southern Africa existed at around the same time among humans who lived over 600 km inland. We report evidence for the intentional collection of non-utilitarian objects (calcite crystals) and ostrich eggshell from excavations of a stratified rockshelter deposit in the southern Kalahari Basin, which we date by optically stimulated luminescence to around 105 ka. Uranium–thorium dating of relict tufa deposits indicates sporadic periods of substantial volumes of fresh, flowing water; the oldest of these episodes is dated to between 110 and 100 ka and is coeval with the archaeological deposit. Our results suggest that behavioural innovations among humans in the interior of southern Africa did not lag behind those of populations near the coast, and that these innovations may have developed within a wet savannah environment.

材料科学 Material Science

Entropic evidence for a Pomeranchuk effect in magic-angle graphene

魔角石墨烯中波梅兰丘克效应的熵证据

作者：Asaf Rozen, Jeong Min Park, Uri Zondiner, Yuan Cao, Daniel Rodan-Legrain, et al.

链接：

https://www.nature.com/articles/s41586-021-03319-3

摘要

20世纪50年代，波梅兰丘克预测，液态氦-3加热后可能会凝固，这与我们的直觉相反。这种效应是由于固相中原子在空间局部的高过量核自旋熵引起的。在此，我们发现在魔角扭曲双层石墨烯中也发生了类似的效应。

使用局部和全局电子熵测量，我们发现，在每摩尔单胞填充近一个电子时，电子熵显著增加到约每单胞1 k B。这个巨大的过量熵被指向其磁源的平面内磁场淬灭。可压缩性随电子密度的变化而急剧下降，伴随着费米能级的重置回到狄拉克点附近，标志着两相之间的清晰边界。

我们将这种跃变映射为电子密度，温度和磁场的函数。这揭示了一个相图，与波梅兰丘克一样，温度和磁场驱动了从低熵电子液体到具有几乎自由磁矩的高熵相关态转变。

相关态的特征是表面上相互矛盾性质的不寻常组合，一些与流动的电子有关——例如缺乏热力学间隙、金属性和狄拉克式的可压缩性——另一些与局部矩有关，例如大的熵及其在磁场下的消失。

Abstract

In the 1950s, Pomeranchuk predicted that, counterintuitively, liquid 3He may solidify on heating. This effect arises owing to high excess nuclear spin entropy in the solid phase, where the atoms are spatially localized. Here we find that an analogous effect occurs in magic-angle twisted bilayer graphene. Using both local and global electronic entropy measurements, we show that near a filling of one electron per moiré unit cell, there is a marked increase in the electronic entropy to about 1 k B per unit cell ( k B is the Boltzmann constant). This large excess entropy is quenched by an in-plane magnetic field, pointing to its magnetic origin. A sharp drop in the compressibility as a function of the electron density, associated with a reset of the Fermi level back to the vicinity of the Dirac point, marks a clear boundary between two phases. We map this jump as a function of electron density, temperature and magnetic field. This reveals a phase diagram that is consistent with a Pomeranchuk-like temperature- and field-driven transition from a low-entropy electronic liquid to a high-entropy correlated state with nearly free magnetic moments. The correlated state features an unusual combination of seemingly contradictory properties, some associated with itinerant electrons—such as the absence of a thermodynamic gap, metallicity and a Dirac-like compressibility—and others associated with localized moments, such as a large entropy and its disappearance under a magnetic field.

Isospin Pomeranchuk effect in twisted bilayer graphene

扭曲双层石墨烯的同位旋波梅兰丘克效应

作者：Yu Saito, Fangyuan Yang, Jingyuan Ge, Xiaoxue Liu, Takashi Taniguchi, Kenji Watanabe, et al.

链接：

https://www.nature.com/articles/s41586-021-03409-2

摘要

在此，我们展示了一种机制来描述魔角扭曲双层石墨烯中自旋和波谷同位旋的有限温度动力学。

值得注意的是，在超晶格填充因子 1附近，高温时电阻率出现峰值，而在低温极限时则没有出现相应的相。倾斜磁场的磁输运和面内磁矩的热力学测量表明，电阻率峰值与系统发展为有限同位旋极化的有限场磁相变有关。这些数据提示了一种波梅兰丘克型机制。

在这种机制中，相对于同位旋未极化的费米液相，铁磁相中的无序同位旋矩的熵在更高的温度下使相稳定。

Abstract

Here we show that a similar mechanism describes the finite-temperature dynamics of spin and valley isospins in magic-angle twisted bilayer graphene. Notably, a resistivity peak appears at high temperatures near a superlattice filling factor of 1, despite no signs of a commensurate correlated phase appearing in the low-temperature limit. Tilted-field magnetotransport and thermodynamic measurements of the in-plane magnetic moment show that the resistivity peak is connected to a finite-field magnetic phase transition at which the system develops finite isospin polarization. These data are suggestive of a Pomeranchuk-type mechanism, in which the entropy of disordered isospin moments in the ferromagnetic phase stabilizes the phase relative to an isospin-unpolarized Fermi liquid phase at higher temperatures.

Diversity-oriented synthesis of polymer membranes with ion solvation cages

基于离子溶剂化聚合物膜的多样性取向合成

作者：Miranda J. Baran, Mark E. Carrington, Swagat Sahu, Artem Baskin, Junhua Song, et al.

链接：

https://www.nature.com/articles/s41586-021-03377-7

摘要

在此，我们描述了一种面向多样性的微孔聚合物膜合成策略，以识别具有FVEs的候选材料，作为锂离子的溶剂笼。

这一策略包括通过曼尼希反应使双联邻苯二酚单体多样化，从而在FVEs中引入锂离子协调功能，加强拓扑聚合使FVEs进入不同的孔结构，以及多种多样的孔几何和介电性能的聚合物反应。

具有离子溶剂化笼的候选膜比控制膜具有更高的离子电导率和更高的阳离子转移数，其中FVEs具有特异性，表明可以克服常规的膜渗透性边界和离子转移的选择性。

Abstract

Here we describe a persity-oriented synthetic strategy for microporous polymer membranes to identify candidates featuring FVEs that serve as solvation cages for lithium ions (Li+). This strategy includes persification of bis(catechol) monomers by Mannich reactions to introduce Li+-coordinating functionality within FVEs, topology-enforcing polymerizations for networking FVEs into different pore architectures, and several on-polymer reactions for persifying pore geometries and dielectric properties. The most promising candidate membranes featuring ion solvation cages exhibited both higher ionic conductivity and higher cation transference number than control membranes, in which FVEs were aspecific, indicating that conventional bounds for membrane permeability and selectivity for ion transport can be overcome.

地球科学 Geoscience

A 200-million-year delay in permanent atmospheric oxygenation

延迟了2亿年的永久大气氧化

作者：Simon W. Poulton, Andrey Bekker, Vivien M. Cumming, Aubrey L. Zerkle, Donald E. Canfield & David T. Johnston

链接：

https://www.nature.com/articles/s41586-021-03393-7

摘要

早期大气氧化发生在以多次全球冰期为标志的长期极端气候不稳定时期，氧浓度最初上升到目前大气水平的 10- 5 以上的时间则推定为24.3亿年前。然而，随后大气氧含量的波动一直持续到大约23.2亿年前，这代表了大气中不可逆氧化的估计时间。

在此，我们通过南非德兰士瓦尔超群的海洋沉积物，对古代早期最后两次冰期的大气和局部海洋氧化还原条件进行了高分辨率重建。利用多重硫同位素和铁-硫-碳系统，我们证明了大约23.2亿年前之后大气氧水平的持续振荡，这与海洋氧化还原化学和气候的主要扰动有关。

因此，在大约2亿年的时间里，氧气水平在目前大气水平的 10- 5 的阈值上下波动。永久的大氧化事件比目前估计的晚了大约1亿年。

Abstract

Early atmospheric oxygenation occurred over a protracted period of extreme climatic instability marked by multiple global glaciations, with the initial rise of oxygen concentration to above 10- 5 of the present atmospheric level constrained to about 2.43 billion years ago. Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago, which represents the estimated timing of irreversible oxygenation of the atmosphere. Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron–sulfur–carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10- 5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated.

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