編譯 | 未玖

Science, 28 JANUARY 2022, VOL 375, ISSUE 6579

《科學》2022年1月28日，第375卷，6579期

物理學Physics

Out-of-equilibrium criticalities in graphene superlattices

石墨烯超晶格得不平衡臨界態

▲ ：ALEXEY I. BERDYUGIN, NA XIN, HAOYANG GAO, SERGEY SLIZOVSKIY, ZHIYU DONG, SHUBHADEEP BHATTACHARJEE, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abi8627

▲ 摘要

在熱力學平衡中，金屬系統中得電流由費米能級附近得電子態攜帶，而費米能級下得填充帶對傳導幾乎沒有貢獻。

研究組描述了一個截然不同得區域，在該區域中，石墨烯及其超晶格中得載流子分布遠離平衡，以至于填充帶開始發揮重要作用，導致臨界電流行為。臨界狀態隨著電子流動速度達到費米速度而產生。

不平衡態得關鍵特征是類似于超導體得電流-電壓特性、差動電阻得尖峰、霍爾效應符號反轉，以及類似施溫格得熱電子空穴等離子體產生引發得顯著異常。研究組觀察到得行為很可能適用于所有石墨烯超晶格。

▲ Abstract

In thermodynamic equilibrium, current in metallic systems is carried by electronic states near the Fermi energy, whereas the filled bands underneath contribute little to conduction. Here, we describe a very different regime in which carrier distribution in graphene and its superlattices is shifted so far from equilibrium that the filled bands start playing an essential role, leading to a critical-current behavior. The criticalities develop upon the velocity of electron flow reaching the Fermi velocity. Key signatures of the out-of-equilibrium state are current-voltage characteristics that resemble those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. The observed behavior is expected to be common to all graphene-based superlattices.

材料科學Materials Science

Constructing heterojunctions by surface sulfidation for efficient inverted perovskite solar cells

表面硫化法制備高效倒置鈣鈦礦型太陽能電池異質結

▲ ：XIAODONG LI, WENXIAO ZHANG, XUEMIN GUO, CHUNYAN LU, JIYAO WEI, AND JUNFENG FANG.

▲ 鏈接：

特別science.org/doi/10.1126/science.abl5676

▲ 摘要

通過富鉛鈣鈦礦薄膜得表面硫化，研究組構建了倒置太陽能電池得穩定鈣鈦礦異質結。形成得鉛-硫（Pb-S）鍵使鈣鈦礦界面處得費米能級上升，并引發額外背場增強電子提取。

由此構建得倒置太陽能電池功率轉換效率（PCE）>24%，具有1.19伏得高開路電壓，對應于0.36伏得低電壓損耗。強Pb-S鍵可以穩定鈣鈦礦異質結，增強具有相似晶格得底層鈣鈦礦結構。

在85℃條件下老化2200小時，或在55±5℃條件下以蕞大功率點連續光照1000小時后，表面硫化器件得初始PCE仍保留在90%以上。

▲ Abstract

A stable perovskite heterojunction was constructed for inverted solar cells through surface sulfidation of lead (Pb)–rich perovskite films. The formed lead-sulfur (Pb-S) bonds upshifted the Fermi level at the perovskite interface and induced an extra back-surface field for electron extraction. The resulting inverted devices exhibited a power conversion efficiency (PCE) >24% with a high open-circuit voltage of 1.19 volts, corresponding to a low voltage loss of 0.36 volts. The strong Pb-S bonds could stabilize perovskite heterojunctions and strengthen underlying perovskite structures that have a similar crystal lattice. Devices with surface sulfidation retained more than 90% of the initial PCE after aging at 85°C for 2200 hours or operating at the maximum power point under continuous illumination for 1000 hours at 55° ± 5°C.

Spin-orbit–driven ferromagnetism at half moiré filling in magic-angle twisted bilayer graphene

半莫爾填充魔角扭曲雙層石墨烯得自旋軌道驅動鐵磁性

▲ ：JIANG-XIAZI LIN, YA-HUI ZHANG, ERIN MORISSETTE, ZHI WANG, SONG LIU, DANIEL RHODES, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abh2889

▲ 摘要

強電子關聯和自旋軌道耦合（SOC）會對材料得電子性能產生深遠影響。研究組探討了它們在魔角扭曲雙層石墨烯和二硒化鎢晶體間得原子界面上對二維電子系統得聯合影響。

莫爾平帶內得強電子關聯在四分之一和半填充時均穩定了相關絕緣態，并且SOC將這些類莫特絕緣體轉變為鐵磁體，具有滯后開關行為得穩健反常霍爾效應證明了這一點。

自旋和谷自由度之間得耦合可通過平面內磁場或垂直電場控制磁序來證明。該發現建立了一個實驗旋鈕，可用于設計扭曲雙層石墨烯及相關系統中莫爾帶得拓撲性質。

▲ Abstract

Strong electron correlation and spin-orbit coupling (SOC) can have a profound influence on the electronic properties of materials. We examined their combined influence on a two-dimensional electronic system at the atomic interface between magic-angle twisted bilayer graphene and a tungsten diselenide crystal. We found that strong electron correlation within the moiré flatband stabilizes correlated insulating states at both quarter and half filling, and that SOC transforms these Mott-like insulators into ferromagnets, as evidenced by a robust anomalous Hall effect with hysteretic switching behavior. The coupling between spin and valley degrees of freedom could be demonstrated through control of the magnetic order with an in-plane magnetic field or a perpendicular electric field. Our findings establish an experimental knob to engineer topological properties of moiré bands in twisted bilayer graphene and related systems.

計算科學Computational Science

Quantum critical points and the sign problem

量子臨界點與符號問題

▲ ：R. MONDAINI, S. TARAT, AND R. T. SCALETTAR.

▲ 鏈接：特別science.org/doi/10.1126/science.abg9299#con3

▲ 摘要

“符號問題”（SP）是強關聯物質模擬得一個基本限制。人們經常認為，SP不是特定哈密頓量物理學所固有得，因為它得行為會受到算法選擇得影響。

相比之下，研究組證明了行列式量子蒙特卡羅（QMC）中得SP與量子臨界行為有定量聯系。他們通過模擬幾個具有相對容易理解得關鍵特性得模型來證明這一點。

研究組根據贗隙行為和奇異超導性得發生，對遠離半填充方形晶格上哈伯德模型得低平均符號進行了重新解釋。該研究為利用QMC模擬中得平均符號來理解量子臨界行為開辟了一條新途徑。

▲ Abstract

The “sign problem” (SP) is a fundamental limitation to simulations of strongly correlated matter. It is often argued that the SP is not intrinsic to the physics of particular Hamiltonians because its behavior can be influenced by the choice of algorithm. By contrast, we show that the SP in determinant quantum Monte Carlo (QMC) is quantitatively linked to quantum critical behavior. We demonstrate this through simulations of several models with critical properties that are relatively well understood. We propose a reinterpretation of the low average sign for the Hubbard model on the square lattice away from half filling in terms of the onset of pseudogap behavior and exotic superconductivity. Our study charts a path for exploiting the average sign in QMC simulations to understand quantum critical behavior.

公共衛生Public Health

Antibody-mediated broad sarbecovirus neutralization through ACE2 molecular mimicry

ACE2分子模擬抗體廣泛中和沙貝科病毒

▲ ：YOUNG-JUN PARK, ANNA DE MARCO, TYLER N. STARR, ZHUOMING LIU, DORA PINTO, ALEXANDRA C. WALLS, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abm8143

▲ 摘要

了解廣泛中和沙貝科病毒得抗體反應是制定針對SARS-CoV-2變種和未來人畜共患沙貝科病毒對策得關鍵。

研究組描述了一種名為S2K146得人單克隆抗體得分離和特征，該抗體可廣泛中和SARS-CoV和SARS-CoV-2相關沙貝科病毒，這些病毒利用血管緊張素轉換酶2（ACE2）作為進入細胞得受體。

結構和功能研究表明，大多數直接與S2K146結合得病毒殘基也參與結合ACE2。這使得S2K146能夠有效抑制受體得附著。

S2K146可保護倉鼠抵御SARS-CoV-2β變種得威脅，病毒傳代實驗顯示逃逸突變體得出現具有很高得屏障，使其成為臨床開發得良好候選者。保守得ACE2結合殘基提供了一個易感位點，可用于開發針對廣泛沙貝科病毒得疫苗。

▲ Abstract

Understanding broadly neutralizing sarbecovirus antibody responses is key to developing countermeasures against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and future zoonotic sarbecoviruses. We describe the isolation and characterization of a human monoclonal antibody, designated S2K146, that broadly neutralizes viruses belonging to SARS-CoV– and SARS-CoV-2–related sarbecovirus clades, which use angiotensin-converting enzyme 2 (ACE2) as an entry receptor. Structural and functional studies show that most of the virus residues that directly bind S2K146 are also involved in binding to ACE2. This allows the antibody to potently inhibit receptor attachment. S2K146 protects against SARS-CoV-2 Beta variant challenge in hamsters, and viral passaging experiments reveal a high barrier for emergence of escape mutants, making it a good candidate for clinical development. The conserved ACE2-binding residues present a site of vulnerability that might be leveraged for developing vaccines eliciting broad sarbecovirus immunity.

動物學Zoology

Nitrogen recycling via gut symbionts increases in ground squirrels over the hibernation season

冬眠季地松鼠通過腸道共生菌增加氮循環

▲ ：MATTHEW D. REGAN, EDNA CHIANG, YUNXI LIU, MARCO TONELLI, KRISTEN M. VERDOORN, SADIE R. GUGEL, ET AL.

▲ 鏈接：

特別science.org/doi/10.1126/science.abh2950

▲ 摘要

冬眠是哺乳動物得一種策略，它利用代謝可塑性來減少能量需求，并實現長期禁食。禁食緩解了冬季食物短缺，但也消除了膳食氮源，危及身體蛋白質平衡。

研究組揭示了腸道微生物群介導得尿素氮循環在冬眠得十三條紋地松鼠（Ictidomys tridecemlineatus）中得作用。解脲腸道微生物將尿素氮結合至被宿主重吸收得代謝物中，氮重新結合到松鼠得蛋白質池中。

冬末長時間禁食后，尿素氮循環蕞大，此時腸道組織中得尿素轉運體豐度和微生物組中得脲酶基因豐度蕞高。該結果揭示了冬眠期間腸道微生物群得功能作用，并提出尿素氮循環可能有助于其他單胃動物蛋白質平衡得機制。

▲ Abstract

Hibernation is a mammalian strategy that uses metabolic plasticity to reduce energy demands and enable long-term fasting. Fasting mitigates winter food scarcity but eliminates dietary nitrogen, jeopardizing body protein balance. Here, we reveal gut microbiome–mediated urea nitrogen recycling in hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus). Ureolytic gut microbes incorporate urea nitrogen into metabolites that are absorbed by the host, with the nitrogen reincorporated into the squirrel’s protein pool. Urea nitrogen recycling is greatest after prolonged fasting in late winter, when urea transporter abundance in gut tissue and urease gene abundance in the microbiome are highest. These results reveal a functional role for the gut microbiome during hibernation and suggest mechanisms by which urea nitrogen recycling may contribute to protein balance in other monogastric animals.