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
石墨烯超晶格的不平衡臨界態
▲ 作者：ALEXEY I. BERDYUGIN, NA XIN, HAOYANG GAO, SERGEY SLIZOVSKIY, ZHIYU DONG, SHUBHADEEP BHATTACHARJEE, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abi8627
▲ 摘要
在熱力學平衡中，金屬系統中的電流由費米能級附近的電子態攜帶，而費米能級下的填充帶對傳導幾乎沒有貢獻。
研究組描述了一個截然不同的區域，在該區域中，石墨烯及其超晶格中的載流子分佈遠離平衡，以至於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。
不平衡態的關鍵特徵是類似於超導體的電流-電壓特性、差動電阻的尖峰、霍爾效應符號反轉，以及類似施溫格的熱電子空穴等離子體產生引發的顯著異常。研究組觀察到的行為很可能適用於所有石墨烯超晶格。
▲ 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
▲ 作者：XIAODONG LI, WENXIAO ZHANG, XUEMIN GUO, CHUNYAN LU, JIYAO WEI, AND JUNFENG FANG.
▲ 連結：
https://www.science.org/doi/10.1126/science.abl5676
▲ 摘要
透過富鉛鈣鈦礦薄膜的表面硫化，研究組構建了倒置太陽能電池的穩定鈣鈦礦異質結。形成的鉛-硫（Pb-S）鍵使鈣鈦礦介面處的費米能級上升，並引發額外背場增強電子提取。
由此構建的倒置太陽能電池功率轉換效率（PCE）>24%，具有1.19伏的高開路電壓，對應於0.36伏的低電壓損耗。強Pb-S鍵可以穩定鈣鈦礦異質結，增強具有相似晶格的底層鈣鈦礦結構。
在85℃條件下老化2200小時，或在55±5℃條件下以最大功率點連續光照1000小時後，表面硫化器件的初始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的自旋軌道驅動鐵磁性
▲ 作者：JIANG-XIAZI LIN, YA-HUI ZHANG, ERIN MORISSETTE, ZHI WANG, SONG LIU, DANIEL RHODES, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abh2889
▲ 摘要
強電子關聯和自旋軌道耦合（SOC）會對材料的電子效能產生深遠影響。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的原子介面上對二維電子系統的聯合影響。
莫爾平帶內的強電子關聯在四分之一和半填充時均穩定了相關絕緣態，並且SOC將這些類莫特絕緣體轉變為鐵磁體，具有滯後開關行為的穩健反常霍爾效應證明了這一點。
自旋和谷自由度之間的耦合可透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，可用於設計扭曲雙層石墨烯及相關係統中莫爾帶的拓撲性質。
▲ 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
▲ 作者：R. MONDAINI, S. TARAT, AND R. T. SCALETTAR.
▲ 連結：https://www.science.org/doi/10.1126/science.abg9299#con3
▲ 摘要
“符號問題”（SP）是強關聯物質模擬的一個基本限制。人們經常認為，SP不是特定哈密頓量物理學所固有的，因為它的行為會受到演算法選擇的影響。
相比之下，研究組證明了行列式量子蒙特卡羅（QMC）中的SP與量子臨界行為有定量聯絡。他們透過模擬幾個具有相對容易理解的關鍵特性的模型來證明這一點。
研究組根據贗隙行為和奇異超導性的發生，對遠離半填充方形晶格上哈伯德模型的低平均符號進行了重新解釋。該研究為利用QMC模擬中的平均符號來理解量子臨界行為開闢了一條新途徑。
▲ 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
▲ 作者：YOUNG-JUN PARK, ANNA DE MARCO, TYLER N. STARR, ZHUOMING LIU, DORA PINTO, ALEXANDRA C. WALLS, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abm8143
▲ 摘要
瞭解廣泛中和沙貝科病毒的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的關鍵。
研究組描述了一種名為S2K146的人單克隆抗體的分離和特徵，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）作為進入細胞的受體。
結構和功能研究表明，大多數直接與S2K146結合的病毒殘基也參與結合ACE2。這使得S2K146能夠有效抑制受體的附著。
S2K146可保護倉鼠抵禦SARS-CoV-2β變種的威脅，病毒傳代實驗顯示逃逸突變體的出現具有很高的屏障，使其成為臨床開發的良好候選者。保守的ACE2結合殘基提供了一個易感位點，可用於開發針對廣泛沙貝科病毒的疫苗。
▲ 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
冬眠季地松鼠透過腸道共生菌增加氮迴圈
▲ 作者：MATTHEW D. REGAN, EDNA CHIANG, YUNXI LIU, MARCO TONELLI, KRISTEN M. VERDOORN, SADIE R. GUGEL, ET AL.
▲ 連結：
https://www.science.org/doi/10.1126/science.abh2950
▲ 摘要
冬眠是哺乳動物的一種策略，它利用代謝可塑性來減少能量需求，並實現長期禁食。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的尿素氮迴圈在冬眠的十三條紋地松鼠（Ictidomys tridecemlineatus）中的作用。解脲腸道微生物將尿素氮結合至被宿主重吸收的代謝物中，氮重新結合到松鼠的蛋白質池中。
冬末長時間禁食後，尿素氮迴圈最大，此時腸道組織中的尿素轉運體丰度和微生物組中的脲酶基因丰度最高。該結果揭示了冬眠期間腸道微生物群的功能作用，並提出尿素氮迴圈可能有助於其他單胃動物蛋白質平衡的機制。
▲ 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.
