鉛-鉛和質子-質子碰撞中

孤立光子觸發的噴注的形狀

本文在噴注與孤立光子協同產生過程中研究了其在鉛-鉛碰撞中噴注的形狀相對於其在質子-質子碰撞中噴注形狀的改變。所使用的數據是CMS實驗組在覈子-核子碰撞的質心能5.02 TeV處收集的。噴注形狀由帶電粒子構建，其軌道橫向動量(p_T)在噴注軸周圍的環形空間中高於1GeV / c，p^jet_T>30GeV / c，並且與p^γ_T> 60GeV /c的孤立光子相關聯。在外圍的鉛鉛碰撞中產生的噴注形狀分佈與質子質子碰撞的結果中是一致的，但是在中心的鉛鉛碰撞中的形狀分佈發生改變。在這些中心鉛鉛事件中，與pp碰撞的結果相比，在距離噴注軸更遠的距離處觀察到更大比例的噴注動量，反映了在重離子碰撞和橫向部分子中產生的部分子介質之間的相互作用。

Jet Shapes of Isolated Photon-Tagged Jets in Pb-Pb and pp Collisionsat √sNN=5.02TeV

A. M. Sirunyan et al. 

(CMS Collaboration)

Phys. Rev. Lett. 122, 152001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.152001

 觀察到B⁰→J/ψK⁺π⁻衰變過程的

模型無關的外來貢獻

使用LHCb探測器收集的積分亮度爲3 fb^-1的質子-質子碰撞數據，本文進行了B⁰→J /ψK⁺π^-衰變過程的角分析。m(K ⁺π^-)譜被分成精細區間。在每個m(K ⁺π^-)區間中，檢查了三維角分佈可以僅僅由K^*共振引起的結構來描述的猜測，在分析中對K⁺π^-系統做出了最小的假設。數據在很大的置信度上反對這一猜測，這意味着在模型無關的情況下觀察到外來的貢獻。檢查m(J /ψπ^-)-m(K⁺π^-)平面給出m(J /ψπ^-)= 4200和4600 MeV附近的結構。

Model-Independent Observation of Exotic Contributions to B0→J/ψK+π− Decays

R. Aaij et al. 

(LHCb Collaboration)

Phys. Rev. Lett. 122, 152002 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.152002

中子物質中有效質量的非微擾提取

Mateusz Buraczynski 等人利用量子蒙特卡洛方法計算了強相互作用中子物質在不同密度處多中子能量以及數個不同激發態的能譜。計算的輸入量是唯像以及手徵兩核子和三核子相互作用。他們利用單粒子能譜來提取中子物質的有效質量。爲了系統地估計提取誤差，他們仔細評估了有限尺寸效應對準粒子色散關係的影響。他們發現，隨着密度的增加，有效質量比從1開始下降。最後，他們將結果與超冷氣體物理以及原子核和中子星物質能量密度泛函理論做了對比。

Nonperturbative Extraction of Effective Mass in Neutron Matter

Mateusz Buraczynski et al.

Phys. Rev. Lett. 122, 152701 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.152701

液體中的量子光力學

[編輯推薦]本文首次利用受限於光學腔的液體——超流體氦，觀察到了量子光力學效應。

本文測量了耦合到光學腔的超流體He中的單個聲學模的量子漲落。具體來說，作者監測了由腔鏡限制的駐波散射的斯托克斯和反斯托克斯光。這些信號的強度（及其相互關聯）表現出聲學波包的零點運動和腔內光的量子反作用的特徵。雖然在固體物體和超冷原子氣體的振動中也觀察到了這些特徵，但是在超流體He中觀察到這些特徵爲利用這種材料的卓越特性來獲得量子光力學的新體系開闢了可能性。

Quantum Optomechanics in a Liquid

A. B. Shkarin, et al.

Phys. Rev. Lett. 122, 153601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153601

三體原子間庫侖衰變的虛光子近似

Interatomic Coulombic decay (ICD) isa mechanism that allows microscopic objects to rapidly exchange energy. When the two objects are distant, the energy transfer between the donor and acceptor species takes place via the exchange of a virtual photon. On the contrary, recent ab initio calculations have revealed that the presence of a third passive species can significantly enhance the ICD rate at short distances dueto the effects of electronic wave function overlap and charge transfer states [Phys. Rev. Lett. 119, 083403 (2017)]. Here, we develop a virtual photon description of three-body ICD, allowing us to investigate retardation and geometrical effects which are out of reach for current ab initio techniques. We show that a passive atom can have a significant influence on the rate of the ICD process at fairly large interatomic distances, due to the scattering of virtual photons off the mediator. Moreover, we demonstrate that in the retarded regime ICD can be substantially enhanced or suppressed depending on theposition of the ICD-inactive object, even if the latter is far from both donorand acceptor species.

Virtual Photon Approximation for Three-Body Interatomic Coulombic Decay

Robert Bennett, et al.

Phys. Rev. Lett. 122, 153401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153401

光學格子中超冷原子的電導率譜

We measure the conductivity of neutral fermions in a cubic optical lattice. Using in situ fluorescence microscopy, we observe the alternating currentresultant from a single-frequency uniform force applied by displacement of a weak harmonic trapping potential. In the linear response regime, aneutral-particle an alog of Ohm’s law gives the conductivity as the ratio of total current to force. For various lattice depths, temperatures, interaction strengths, and fillings, we measure both real and imaginary conductivity, up to a frequency sufficient to capture the transport dynamics within the lowest band. The spectral width of the real conductivity reveals the current dissipation rate in the lattice, and the integrated spectral weight is related to thermodynamic properties of the system through a sum rule. The global conductivity decreases with increased band-averaged effective mass, which at high temperatures approaches a T-linear regime. Relaxation of current is observed to require a finite lattice depth, which breaks Galilean invariance and enables damping through collisions between fermions.

Conductivity Spectrum of Ultracold Atoms in an Optical Lattice

Rhys Anderson, et al.

Phys. Rev. Lett. 122, 153602 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153602

離子基光腔光子數量子數傳感器

本文將單個捕獲離子色散耦合到光學腔內，以非破壞性的方式提取關於腔光子數分佈的信息，再通過Ramsey光譜法測量該離子經歷的依賴於光子數的交流斯塔克位移。作者首先利用這些測量來獲得離子與腔相互作用強度，接着重建了相干態和一個具有混合熱相干統計的態的腔光子數分佈，發現與校準態重疊超過99％。

Ion-Based Quantum Sensor for Optical Cavity Photon Numbers

Moonjoo Lee, et al.

Phys. Rev. Lett. 122, 153603 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153603

異常面感知將靈敏度與穩健性相結合

異常點（EPs）是非厄米物理中出現的奇點。目前的研究工作僅集中於支持孤立EPs的系統，其特徵在於對外部擾動的敏感性增加，這使得它們成爲構建下一代光學傳感器的潛在候選者。在另一方面，這個特徵也是這些設備的致命弱點：它們對製造誤差和實驗不確定性非常敏感。爲了克服這個問題，Q. Zhong等人引入了一種新的設計概念，用於實現光子EPs，結合了實際使用所需的穩健性和標誌性靈敏度。特別地，他們提出的結構展示了在更大嵌入空間中的Jordan EPs超曲面，並且具有以下特徵：（1）大量非期望的擾動沿着異常表面（ES）移動操作點，因此，將系統留在另一個EP上，這就解釋了它的穩健性; （2）由於背反射或反向散射引起的擾動迫使工作點離開ES，從而提高靈敏度。重要的是，他們提出的幾何結構使用標準光子元件相對容易實現，並且設計概念可以擴展到其他物理平臺，例如微波或聲學。(江柯縉)

Sensing with Exceptional Surfaces in Order to Combine Sensitivity with Robustness

Q. Zhong, et al.

Phys. Rev. Lett. 122, 153902 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153902

耗散系統中相干結構的

非線性傅里葉變換分析

Using the cubic Ginzburg-Landau equation as an example, we demonstrate how the inverse scattering transform can be applied to characterize coherent structures in dissipative nonlinear systems. Using this approach one can reducethe number of the effective degrees of freedom in the system when the dynamicis dominated by the coherent structures, even if they are embedded in the dispersive waves and demonstrate unstable behavior. (江柯縉)

Nonlinear Fourier Transform for Analysis of Coherent Structures in Dissipative Systems

I. S. Chekhovskoy, et al.

Phys. Rev. Lett. 122, 153901 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153901

關聯噪聲多模系統中的相干波傳播

多模系統中的缺陷導致模式混合和傳播模式之間的干涉。這種無序通常以有限的相關時間（量子進化）或相關長度（在近軸演化中）爲特徵。Yaxin Li等人證明在模式空間中傳播的初始激發的大尺度動力學可以通過短程相干動力學來調製。特別是他們揭示了初始模式從指數到冪律彈道式衰變的普適轉變過程。他們的結果適用於各種波動物理框架，從多模光纖到量子點和量子生物學。(江柯縉)

Coherent Wave Propagation in Multimode Systems with Correlated Noise

Yaxin Li, et al.

Phys. Rev. Lett. 122, 153903 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153903

通過動量空間高繞組實現寬帶拓撲慢光

Slow-light waveguides can strongly enhance light-matter interaction, but suffer from a narrow bandwidth, increased backscattering, and Anderson localization. Edge states in photonic topological insulators resist backscattering and localization, but typically cross the bulk band gap over a single Brillouin zone, meaning that slow group velocity implies narrow-band operation. Here we show theoretically that this can be circumvented via an edgetermination that causes the edge state to wind many times around the Brillouinzone, making it both slow and broadband. (江柯縉)

Broadband Topological Slow Light through Higher Momentum-Space Winding

Jonathan Guglielmon, et al.

Phys. Rev. Lett. 122, 153904 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153904

膜諧振器非線性彎曲振動的空間調製

Fan Yang等人研究了在強非線性區域強驅動下機械諧振器的振動。通過對矩形氮化硅膜諧振器振動狀態的成像，利用光學干涉法對其頻率響應進行分析，表明在提高驅動強度的同時，膜採用了一種特殊的偏轉模式，該模式由疊加在基模鼓頭形狀上的同心環形成。這種圓對稱性不能描述爲少量被激發線性本徵模的疊加。此外，膜的不同部分以不同驅動頻率倍數振動，他們稱之爲“泛音局域化”。他們引入了一個基於很小數量的有效非線性諧振器耦合的唯像模型，代表膜的不同部分，正確地描述了實驗觀察。(江柯縉)

Spatial Modulation of Nonlinear Flexural Vibrations of Membrane Resonators

Fan Yang, et al.

Phys. Rev. Lett. 122, 154301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.154301

紅外泵浦增強拉曼效應

We propose a method for increasing Raman scattering from an ensemble of molecules by up to 4 orders of magnitude. Our method requires an additional coherent source of IR radiation with the half-frequency of the Stokes shift. This radiation excites the molecule electronic subsystem that in turn, via Fröhlich coupling, parametrically excites nuclear oscillations at a resonant frequency. This motion is coherent and leads to a boost of the Raman signal in comparison to the spontaneous signal because its intensity is proportional to the squared number of molecules in the illuminated volume.（蔡若冰）

Enhancement of the Raman Effect by Infrared Pumping

V. Yu. Shishkov, et al.

Phys. Rev. Lett. 122, 153905 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153905

具有奇粘性不可壓縮流體的

自由表面變分原理

Abanov等人提出了不可壓縮流體動力學的變分和哈密頓公式，流體具有自由表面和未消失的奇粘性。這裏表明，在變分原理中，奇粘度貢獻對應於幾何邊界項。這些邊界項修改了Zakharov的泊松括號，導致一種新型邊界動力學。修正的邊界條件具有一種自然的幾何解釋，描述了自由表面上與表面本身角速度成比例的附加壓力。這些邊界條件被認爲是普適的，因爲所提出的流體動力作用完全由系統的對稱性決定。（蔡若冰）

Free-Surface Variational Principle for an Incompressible Fluid with Odd Viscosity

Alexander G. Abanov, et al.

Phys. Rev. Lett. 122, 154501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.154501

分層液體中的油滴彈跳及其突然停止

當浸入另一種存在濃度梯度的液體中時，液滴可以自行推進。在這裏，Diddens等人報告了在垂直分層的乙醇-水混合物中自推進油滴的實驗和數值研究：首先，液滴由於重力而緩慢下沉，但是在達到其密度匹配位置之前，突然跳起。更值得注意的是，液滴以不斷增加的跳躍距離反覆彈跳，直到大約30分鐘後它突然停止。可以確定液滴-液體界面處的Marangoni應力是導致跳躍的原因：它的強度呈指數增長，因爲它可以拉下富含乙醇的液體，從而進一步提高其強度。跳躍過程可以重複，因爲重力恢復了系統狀態。最後，還解釋了跳躍液滴的突然停止。此研究結果表明，在沒有壁面或明顯界面的連續介質中，有一種突出的液滴反彈。（蔡若冰）

Bouncing Oil Droplet in a Stratified Liquid and its Sudden Death

Yanshen Li, et al.

Phys. Rev. Lett. 122, 154502 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.154502

電磁多極的奇異性與龐加萊指數

電磁多極已被廣泛用作整個光子學的基本語言，其中諸如輻射圖和偏振分佈的一般特徵通常是已知的，而它們的奇點和拓撲特性一般無人觸及。在此，Chen等人繪製了不同階數多極輻射的所有奇點，識別它們的指數，並明確表明整個動量範圍內指數和總是2，與龐加萊—霍普夫定理一致。從這些顯示的屬性，Chen等人將連續體中形成束縛態歸因於多極奇點與開放輻射通道間的重疊。這種見解揭示了多極奇點指數與那些束縛態拓撲電荷之間的微妙等價。這裏的工作融合了多極和拓撲這兩個基本和普遍使用的概念，爲光子學內外許多多極相關領域帶來無法估量的潛在機會。（蔡若冰）

Singularities and Poincaré Indices of Electromagnetic Multipoles

Weijin Chen, et al.

Phys. Rev. Lett. 122, 153907 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153907

Si₃N₄環形諧振腔中的強非線性耦合

We demonstrate that nondegenerate four-wave mixing in a Si₃N₄ microring resonator can result in a nonlinear coupling rate between two optical fields exceeding their energy dissipation rate in the resonator, corresponding to strong nonlinear coupling. We demonstrate that this leads to a Rabi-like splitting, for which we provide a theoretical descriptionin agreement with our experimental results. This yields new insight into the dynamics of nonlinear optical interactions in microresonators and access to novel phenomena.（蔡若冰）

Strong Nonlinear Coupling in Si₃N₄ Ring Resonator

Sven Ramelow, et al.

Phys. Rev. Lett. 122, 153906 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.153906

強相對論電子束與超強激光脈衝

單次相互作用過程中的極化問題研究

Li等人在量子輻射主導機制下，研究了強相對論電子束與超強激光脈衝對撞過程中的自旋極化。通過在局部恆定場近似中應用自旋分辨輻射概率，作者們開發了一種可用於模擬任意電磁場中的電子輻射自旋效應的蒙特卡羅方法。由於自旋相關的輻射反應，所施加的橢圓偏振激光脈衝使最初未極化的電子束極化，並沿着傳播方向將其分成兩個相反的橫向極化部分，其分裂角度約爲幾十毫弧度。因此，利用真實的激光脈衝可以在數十飛秒內產生偏振度超過70%的緻密電子束。本文所提出的方法給出了一種利用現有激光設備進行相對論電子束極化的方法。（王科力）

Ultrarelativistic Electron-Beam Polarization in Single-Shot Interaction with an Ultraintense Laser Pulse

Y. F. Li, et al.

Phys. Rev. Lett. 122, 154801 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.154801

利用Thomson散射測量低密度

等離子體的皮秒熱力學參量

Davies等人通過相干Thomson散射測量了激光等離子體中電子密度和溫度的快速演化。利用脈衝前沿傾斜補償光譜儀首次實現了皮秒時間分辨測量，測量結果揭示了等離子體-波動力學中等離子體從最初的冷碰撞狀態到準靜態無碰撞狀態的轉變。將Thomson散射光譜與通過理論計算（使用傳統的Bhatnagar-Gross-Krook（BGK）碰撞算子或嚴格的朗道碰撞項）得到的波動譜進行比較發現：在最大碰撞條件下BGK模型高估了50％的電子溫度。（王科力）

Picosecond Thermodynamics in Underdense Plasmas Measured with Thomson Scattering

A. S. Davies, et al.

Phys. Rev. Lett. 122, 155001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.155001

通過單色二維Kα輻射圖像

揭示短脈衝激光等容加熱機制

Sawada等人利用二維窄帶X射線成像和X射線光譜學方法研究了高強度亞皮秒激光對薄鈦箔的快速加熱過程。通過使用調整到4.51keV Ti Kα的新型單色成像診斷器，成功地將固體密度等離子體橫向直徑約35μm、深度爲2μm的主要電離區域（〈Z〉>17±1）圖像化。實驗結果和二維碰撞particle-in-cell模擬表明，強激光對固體箔進行快速等容加熱時，在脈衝結束後的幾皮秒內，熱預等離子體的熱擴散作用使固體鈦達到高電離狀態。Kα的偏移和缺失不能用現有的原子物理模型來解釋。僅當包括具有⟨Z⟩= 17的閾值電離的Kα偏移的唯象模型時，才能再現測量的Kα圖像。這項工作揭示了等容加熱非平衡等離子體的電離態和電子溫度的獨立增加機制。（秦晨）

Monochromatic 2D Kα Emission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism

H. Sawada, et al.

Phys. Rev. Lett. 122, 155002 (2019)

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.122.155002

無ELM高性能託卡馬克等離子體中

低n邊界諧頻振盪的激發機制

Brunetti等人分析了準H模中低n邊界諧頻振盪（EHO）的激發機制。結果表明，在離子流類多普勒效應的約束下，逆磁效應和極向MHD流的共同作用將導致短波模的穩定，從而允許低n擾動的增長。本文中的分析基於託卡馬克環位型，考慮的影響因素包括：大的邊緣壓強梯度，局域平坦的安全因子剖面和逆磁流，剪切平行和E×B旋轉，等離子體和理想導體壁間的真空區域，以及分界面等。（秦晨）

Excitation Mechanism of Low-n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

D. Brunetti, et al.

Phys. Rev. Lett. 122, 155003 (2019)

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.122.155003 

Sine-Gordon模型

和Lukyanov-Zamolodchikov猜想的

非微擾函數的重整化羣方法

作者用非微擾函數的重整化羣方法(FRG)來研究量子sine-Gordon模型。這種方法的基準是將他們對孤子以及最輕呼吸（孤子-反孤子束縛態）質量的研究成果與精確的結果做對比。然後，他們檢驗了塊狀相（n是整數並且2π⁄β表明了sine-Gordon模型中勢場的週期性）中指數場條件下Lukyanov-Zamolodchikov猜想期望值〈e^i⁄2nβφ 〉的有效性。他們發現FRG結果與猜想之間的相對與絕對不一致的最小值小於0.01。（毛慧燦）

Nonperturbative Functional Renormalization-Group Approach to the Sine-Gordon Model and the Lukyanov-Zamolodchikov Conjecture

R. Daviet and N. Dupuis

Phys. Rev. Lett. 122, 155301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.155301

通過打破山谷分配展現泊松比開關的

摺疊模式幾何力學

[編輯推薦]：摺疊圖案產生具有可在大範圍內調節的特性的超材料。

對特定摺疊圖案構型空間的探索[例如Miuraori(具有平行四邊形摺疊模式的平面)和eggbox]使得科學技術有了顯著進步。爲了擴大摺疊設計空間，Pratapa等人提出了一個名爲“Morph”的模式，它結合了其父模式的特性。他們介紹了一種四頂點摺疊晶胞，它在Miura模式和eggbox模式之間連續變化，形成了一類同倫構型。這是通過改變其中一個摺痕的峯和谷的分配來實現的，從而通過大範圍的正負泊松比實現平滑的切換。Pratapa等人給出了平面內拉伸和平面外彎曲的泊松比的精確解析表達式，發現它們大小相等，符號相反。此外，他們證明通過使用動力學分岔將上述每種模式下的兼容單胞結合，可以創建出具有獨特特性的混合摺疊模式，例如拓撲模式鎖定和泊松比的可調切換。（劉瑞）

Geometric Mechanics of Origami Patterns Exhibiting Poisson’s Ratio Switch by Breaking Mountain and Valley Assignment

P. P. Pratapa, K. Liu, G. Paulino

Phys. Rev. Lett. 122, 155501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.155501

極端張力下MoS₂熱導率的增強

由於範德瓦爾斯（vdW）固體的層間鍵合作用很弱，因此對外界的刺激例如應變非常敏感。對vdW固體熱性質應變調控的實驗研究目前爲止還未被報導過。在鑽石鐵砧單元中9%靜水壓橫向壓縮應變以下的範圍，利用皮秒瞬態熱反射測量技術可以觀測到MoS₂塊體裏橫向熱導率從3.5 Wm^-1K^-1到25 Wm^-1K^-1 的增強。第一性原理計算和相干聲子光譜實驗揭示這一顯著變化源於應變增強的層間相互作用極大地修正了聲子色散，並且由於沿着橫向方向的分解效應導致了聲子壽命的衰減。電子熱導率變化的貢獻則可以忽略不計。作者的結果表明，在多物理器件中可能實現並行地調控vdW固體的結構、熱和電特性。(曹錦)

Thermal Conductivity Enhancement in MoS₂ under Extreme Strain

Xianghai Meng, et al.

Phys. Rev. Lett. 122, 155901 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.155901

具有任意Rashba和Dresselhaus自旋軌道

相互作用的量子阱中的解析弱局域磁導率

Marinescu等人推導出一個對於垂直磁場中具有任意Rashba α和Dresselhaus β（線性）和β₃（立方）自旋-軌道相互作用耦合的二維電子系統的磁導率進行弱局域（WL）校正的解析表達式。在具有面內z軸且α=β時爲高自旋對稱方向的參考系統中，他們設計了一種新算法來計算導致WL的三個獨立貢獻。反局域性被沿z方向自旋弛豫相關的項抵消，只依賴於α-β。另一項是由兩個相同的散射模式產生，其特徵在於作爲散射動量方向顯式函數的自旋弛豫速率。對於GaAs量子阱的數據研究，發現了極好的一致性，其中特別的是，他們的理論正確地獲取了WL曲線的最小值隨α/β的變化。這表明有效自旋弛豫速率的各向異性是理解自旋-軌道耦合在輸運中的效應的基礎。（方子明）

Closed-Form Weak Localization Magneto conductivity in Quantum Wells with Arbitrary Rashba and Dressel haus Spin-Orbit Interactions

D. C. Marinescu et al.

Phys. Rev. Lett. 122, 156601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.156601

有限距離相互作用勢的BCS理論中

普遍存在的超導圓頂

藉助數學物理學的最新進展，Langmann等人給出了一種能夠在有限距離相互作用引起s波超導的體系解析求解線性BCS能隙方程的可靠方法。作者證明，標準BCS理論預言的超導臨界溫度Tc隨載流子密度n單調增長的關係是由局域相互作用勢假設造成的人爲後果，而任何明確定義的非局域勢都會引發超導圓頂，即超導臨界溫度在有限摻雜的情況下達到最大值並在大摻雜濃度下趨於零。這意味着超導圓頂的出現並不一定需要競爭序或者新奇超導性。（李鬆）

Ubiquity of Superconducting Domes in the Bardeen-Cooper-Schrieffer Theory with Finite-Range Potentials

Edwin Langmann et al.

Phys. Rev. Lett. 122, 157001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.157001

磁摻雜揭示玻色超導-絕緣轉變

附近的準粒子屏蔽

Experiments show that the Cooper pair transport in the insulator phase that forms at thin film superconductor to insulator transitions (SIT) is simply activated. The activation energy T₀ depends on the microscopic factors that drive Cooper pair localization. To test proposed models, we investigated how a perturbation that weakens Cooper pair binding, magnetic impurity doping, and phase frustration affects T₀. The data show that T₀ decreases monotonically with doping in films tuned farther from the SIT and increases and peaks in films that are closer to the SIT critical point. The observations provide strong evidence that the bosonic SIT in thin films is a Mott transition drivenby Coulomb interactions that are screened by virtual quasiparticle excitations. This dependence on underlying fermionic degrees of freedom distinguishes these SITs from those in microfabricated Josephson Junction arrays, cold atom systems, and likely in high temperature superconductors with nodes in their quasiparticle density of states.

Quasiparticle Screening near a Bosonic Superconductor-Insulator Transition Revealed by Magnetic Impurity Doping

X. Zhang et al.

Phys. Rev. Lett. 122, 157002 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.157002

Sr₃IrRuO₇中過阻尼反鐵磁奇異金屬態

The unconventional electronic ground state of Sr₃IrRuO₇ is explored via resonant x-ray scattering techniques and angle-resolved photoemission measurements. As the Ru content approaches x=0.5 in Sr₃(Ir_1−xRu_x)₂O₇, intermediate to the J_eff=1/2 Mott state in Sr₃IrRuO₇ and the quantum critical metal in Sr₃IrRuO₇, a thermodynamically distinct metallic state emerges. The electronic structure of this intermediate phase lacks coherent quasiparticles, and charge transport exhibits a linear temperature dependence over a wide range of temperatures. Spin dynamics associated with the long-range antiferromagnetism of this phase show nearly local, overdamped magnetic excitations and an anomalously large energy scale of 200 meV—an energy far in excess of exchange energies present within either the Sr₃IrRuO₇ or Sr₃IrRuO₇ solid-solution end points. Overdamped quasiparticle dynamics driven by strong spin-charge coupling are proposed to explain the incoherent spectral features of the strange metal state in Sr₃IrRuO₇.

Overdamped Antiferromagnetic Strange Metal State in Sr₃IrRuO₇

Julian L. Schmehr et al.

Phys. Rev. Lett. 122, 157201 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.157201

亞鐵磁體超快退磁過程中的角動量流

自從Beaurepaire等人發現利用飛秒激光脈衝可以使得鐵磁金屬鎳在亞皮秒時間尺度上發生退磁現象以來，越來越多的注意力被投放到超快磁化動力學過程的研究中。近年來，對亞鐵磁GdFeCo合金的研究表明，超快激光誘導的磁化翻轉是由瞬間類鐵磁態誘導的，且這種翻轉完全是熱驅動的，不需要任何其他外部刺激，只依賴於稀土和過渡金屬子晶格之間的交換耦合作用。但是，到目前爲止，對超快退磁和磁化翻轉過程中角動量的流動方式仍然不清楚。本文中，作者藉助於時間分辨的軟X射線磁圓二色性測量技術對亞鐵磁GdFeCo合金在飛秒激光誘導退磁過程中的磁化動力學行爲進行研究。實驗中，作者分別對Fe和Gd元素中自旋、軌道磁矩的動力學行爲進行了觀察和記錄。作者發現，在退磁過程的前幾百飛秒內，自旋和軌道角動量可以完全轉移到晶格，爲Fe和Gd之間缺乏原子間角動量交換提供了有力的證據。（劉錢）

Angular Momentum Flow During Ultrafast Demagnetization of a Ferrimagnet

M. Hennecke et al.

Phys. Rev. Lett. 122, 157202 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.157202

ZnO薄膜中非局域和帶簡併

引起的光物質相互作用協同增強

This study aims to reveal the full potential of ZnO as an ultrafast photofunctional material. Based on nonlocal response theory to incorporate the spatially inhomogeneous quality of the samples coupled with experimental observations of linear and nonlinear optical responses, we establish the ultrafast radiative decay of excitons in ZnO thin films that reaches the speed of excitonic dephasing at room temperature intypical semiconductors at a couple tens of femtoseconds. The consistency between the observed delay-time dependence of the transient-grating signals and the theoretical prediction reveals that the ultrafast radiative decay is due to the synergetic effects of the giant light-exciton interaction volume and the radiative coupling between multicomponent excitons.

Synergetic Enhancement of Light-Matter Interaction by Nonlocality and Band Degeneracy in ZnO Thin Films

Takashi Kinoshita et al.

Phys. Rev. Lett. 122, 157401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.157401

機械記憶的強度在軟玻璃的屈服點處最大

Mukherji等人通過實驗證明，單個和多重機械記憶都可以編碼在無定形氣泡筏中，該氣泡筏是一種受到振盪應變的軟玻璃原型。根據最近的數值結果，作者發現多重機械記憶可以在沒有外部噪聲的條件下形成。通過系統地研究橫跨屈服的一系列訓練應變振幅的記憶形成，作者發現記憶的明顯特徵甚至超出屈服。最引人注目的是，對於屈服應變附近的訓練振幅，系統回收記憶的程度是最大的，並且是系統在編碼過程中進行重組的空間範圍的直接結果。作者的研究進一步表明，力網絡在訓練中的演化對於堵塞包裝中的記憶形成起着決定性作用。

Strength of Mechanical Memories is Maximal at the Yield Point of a Soft Glass

Srimayee Mukherji, et al.

Phys. Rev. Lett. 122, 158001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.158001

受驅動遠離平衡的分子振動的

Fröhlich凝聚體中的量子漲落

當系統由外部泵浦時，Fröhlich發現極性振動在最低頻率模式下發生明顯的凝聚。爲了充分了解Fröhlich凝聚，人們需要超越平均場的層次來描述關鍵行爲以及量子漲落。擁有非線性的振動模式之間的能量重新分佈被證明對於實現凝聚和聲子數分佈是必不可少的，揭示了利用泵浦從準熱到超泊松統計的轉變。Zhang等人進一步研究了Fröhlich凝聚體的光譜特性，該特性通過窄線寬顯示出來。這給出了凝聚體的長時相干性和集體運動。最後，作者展示了蛋白質，如牛血清白蛋白和溶菌酶，最可能成爲通過拉曼或紅外光譜觀察太赫茲體系中這種集體模式的候選者。

Quantum Fluctuations in the Fröhlich Condensate of Molecular Vibrations Driven Far From Equilibrium

Zhedong Zhang, et al.

Phys. Rev. Lett. 122, 158101 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.158101

從可感知的動力學中

檢測隱藏單元和網絡規模

網絡動力系統的單元數目的大小，可以說是最基本的屬性。然而，網絡的許多單元往往在實驗上不可獲得，使得網絡規模通常是未知的。在這裏，Haehne等人引入一個檢測矩陣，該矩陣可以適當地安排來自可獲得的單元子集的多個瞬態時間序列，通過匹配秩約束來檢測網絡規模。作者所提的方法是不依賴於模型的，可用於各種系統類型和交互拓撲，適用於固定點附近的非平穩動力學，以及週期的和混沌的集體運動。即使只有少數單元是可感知的，對於同時表現出非線性、異質性和噪聲的系統，精確的規模檢測是可行的。作者演示了該方法在已成爲範式的一類生化反應網絡中的適用性。

Detecting Hidden Units and Network Size from Perceptible Dynamics

Hauke Haehne, et al.

Phys. Rev. Lett. 122, 158301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.158301

切比雪夫近似與模型預測的全局幾何

Complex nonlinear models are typically ill conditioned or sloppy; their predictions are significantly affected by only a small subset of parameter combinations, and parameters are difficult to reconstruct from model behavior. Despite forming an important universality class and arising frequently inpractice when performing a nonlinear fit to data, formal and systematic explanations of sloppiness are lacking. By unifying geometric interpretations of sloppiness with Chebyshev approximation theory, we rigorously explain sloppiness as a consequence of model smoothness. Our approach results in universal boundson model predictions for classes of smooth models, capturing global geometric features that are intrinsic to their model manifolds, and characterizing a universality class of models. We illustrate this universality using three models from disparate fields (physics, chemistry, biology): exponential curves, reaction rates from an enzyme-catalyzed chemical reaction, and an epidemiology model of an infected population.

Chebyshev Approximation and the Global Geometry of Model Predictions

Katherine N. Quinn, et al.

Phys. Rev. Lett. 122, 158302 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.158302

自相似過程遵循離散對數空間中的冪律分佈

Cities, wealth, and earthquakes follow continuous power-law probability distributions such as the Pareto distribution, which arecanonically associated with scale-free behavior and self-similarity. However, many self-similar processes manifest as discrete steps that do not produce acontinuous scale-free distribution. We construct a discrete power-law distribution that arises naturally from a simple model of hierarchical self-similar processes such as turbulence and vasculature, and we derive the maximum-likelihood estimate (MLE) for its exponent. Our distribution isself-similar, in contrast to previously studied discrete power laws such as the Zipf distribution. We show that the widely used MLE derived from the Pareto distribution leads to inaccurate estimates in systems that lack continuous scale invariance such as branching networks and data subject to logarithmicbinning. We apply our MLE to data from bronchial tubes, blood vessels, and earthquakes to produce new estimates of scaling exponents and resolve contradictions among previous studies.

Self-Similar Processes Follow a Power Law in Discrete Logarithmic Space

M. Newberry and Van M. Savage

Phys. Rev. Lett. 122, 158303 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.158303

氣候模型中憂鬱態之間的轉變：

調和確定性和隨機性觀點

衆所周知，在當前的天文構象中，地球處於一個可以實現兩個漸近態的體系中。我們生活的溫暖態與冰雪覆蓋的雪球態競爭。由於正的冰反照率反饋，存在雙穩態。在先前對中等複雜性氣候模型進行的研究中，Lucarini等人識別出分離共存氣候的不穩定氣候態（憂鬱態melancholia state），並研究了其動態特性和幾何特性。憂鬱態的地球被冰覆蓋到中緯度，該態吸引起始於區域邊界的軌跡。在這篇快報中，作者研究了隨機擾動控制入射太陽輻射強度的參數如何影響氣候的穩定性。作者研究了溫暖態和雪球態之間的轉變，並詳細地分析了噪聲引起的從相應吸引域逃逸的特性。作者確定了轉變的最可能路徑，並發現有證據表明憂鬱態起到入口的作用，類似於能量地貌中的鞍點。

Transitions across Melancholia States in a Climate Model: Reconciling the Deterministic and Stochastic Points of View

Valerio Lucarini and Tamás Bódai

Phys. Rev. Lett. 122, 158701 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.158701

降雨的精確可解記錄模型

Daily precipitation time series are composed of null entries corresponding to dry days and nonzero entries that describe the rainfall amounts on wet days. Assuming that wet days follow a Bernoulli process with success probability p, we show that the presence of dry days induces negative correlations between record-breaking precipitation events. The resulting nonmonotonic behavior of the Fano factor of the record counting process is recovered in empirical data. We derive the full probability distribution P(R,n) of the number of records R_n up to time n, and show that for large n, it converges to a Poisson distribution with parameter ln(pn). We also study in detail the joint limit p→0, n→∞, which yields a random record model in continuoustime t=pn.

Exactly Solvable Record Model for Rainfall

Satya N. Majumdar, et al.

Phys. Rev. Lett. 122, 158702 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.158702