3He超流體、量子自旋液體、晶格 QCD 、 光連續譜束縛態 | 本週物理講座

1

報告人：Hiroki Ikegami，Institute of Physics，Chinese Academy of Sciences

時間：12月3日（週二）10:00

單位：中國科學院物理研究所

地點：懷柔園區X1樓101會議室

摘要：

The p-wave superfluid 3He exhibits a number of exotic quantum phenomena which are intimately related to symmetry breaking and nontrivial topology, and their understanding has significant implications not only for condensed matter physics but also for particle physics and cosmology. In this talk, I will present two experimental studies of novel phenomena arising from symmetry breaking and nontrivial topology of superfluid 3He. First, I will present the first direct demonstration of chiral symmetry breaking in Weyl superfluid 3He-A phase by showing that electrons immersed in superfluid 3He-A exhibit an anomalous Hall effect. Second, I will present the direct observation of Majorana surface states formed at a free surface of topological 3He-B phase by using electrons trapped at the surface.

報告人簡介：

Hiroki Ikegami is a professor at Institute of Physics (IOP), Chinese Academy of Sciences (CAS). He received B. S., M. S., and Ph. D. from the University of Tokyo, all in applied physics. He was an assistant professor at the University of Tokyo in 1999–2001, and a research scientist and a senior research scientist at RIKEN in 2001–2022. Since 2022, he is a professor at IOP, CAS. He received a Young Scientist Award of the Physical Society of Japan in 2009 and JSPS (Japan Society for the Promotion of Science) Prize in 2015.

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報告人：David Smith，法國國家科研中心

時間：12月3日（週二）15:30

單位：北京大學物理學院

地點：KIAA-auditorium

摘要：

Over 300 pulsars are seen to pulse in GeV gamma rays acquired with the Large Area Telescope (LAT) on the Fermi satellite. Many more may be waiting for discovery: of the >2000 LAT sources with no counterpart known at other wavelengths, hundreds are non-variable, with pulsar-like spectral shapes and sky distributions. In addition, population syntheses typically predict as many as twice the current LAT pulsar sample. However, detecting gamma-ray pulsations will be difficult for most of the new ones, whether through blind searches of the gamma-ray data, or using long-term phase-connected rotation ephemeredes for radio pulsars. I will describe the sample of gamma-ray pulsars in the 3rd LAT Pulsar Catalog, and the ongoing work to transform candidates into discoveries. I will focus on the opportunities that FAST provides to identify the radio-faint, gamma-loud pulsars hidden in the LAT data, highlighting some of the science that further discoveries enable.

報告人簡介：

David A. Smith works with NASA’s Fermi satellite at the Laboratoire d’Astrophysique de Bordeaux, a laboratory of the French National Center for Scientific Research (CNRS). The Large Area Telescope (LAT), Fermi’s primary instrument, is sensitive to gamma-ray photons in the GeV energy range. Fermi was called GLAST before being launched from Cape Canaveral in June, 2008. Smith grew up in Berkeley, California, and obtained a B.A. in Physics from the University there. He received his PhD from the University of Illinois at Urbana-Champaign in 1988, for work on the CDF experiment at the Fermilab proton-antiproton collider that contributed to the discovery of the Top quark. He was part of a small team that built and commissioned the then-largest muon detector in the world, specializing in the front-end and trigger electronics. He was a postdoctoral fellow at the National Institute for Nuclear Physics (INFN) in Pisa, Italy for six years. David Smith switched to gamma ray astrophysics in 1991, developing innovative telescopes to exploit atmospheric Cherenkov light. He worked on experiments on the island of La Palma in the Canaries, and led the reconversion of a solar facility in the French Pyrenees into a gamma-ray telescope, focussing on the data acquisition electronics. He joined the CNRS staff in 1995. The Bordeaux group discovered of a large number of gamma-ray pulsars, widely published. Smith organised an international consortium to time pulsar rotations using radio telescopes around the world. Smith also led the testing of Fermi’s GPS-based precision clocks. His primary research interest is the study of gamma-ray pulsars. He also explores the nature of the approximately 2000 GeV LAT sources with no presently known counterpart at other wavelengths. To this end, he has been looking into massive star formation regions (SFRs) as gamma-ray emitters since late 2023.

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報告人：樑劍，華南師範大學

時間：12月3日（週二）15:00

單位：中國科學院高能物理研究所

地點：圖書館樓319會議室

摘要：

Understanding the asymptotic high-energy behavior of hadron-hadron total cross sections is one of the most challenging open problems in strong interaction physics. The optical theorem connects hadronic total cross sectionsto hadron elastic scattering amplitudes. In our work, we calculate, from first principles, the Euclidean correlation functions of Wilson loops that can be used to reconstruct high-energy meson-meson scattering amplitudes in a functional-integral approach. Additionally, considering the crossing symmetry of the loop-loop correlation functions, we clearly observe odderon exchange in the high-energy soft interactions between two quark dipoles.

報告人簡介：

樑劍，華南師範大學量子物質研究院研究員，博士生導師。2010年本科畢業於南開大學，2015年於中國科學院高能物理研究所獲得博士學位，後在美國肯塔基大學從事博士後研究。2020年入職華南師範大學，2022年獲得國家優秀青年基金資助。主要從事格點量子色動力學相關的研究工作，致力於從第一性原理出發通過大規模數值模擬研究強子結構與性質。

4

報告人：Zhewei Yin，Argonne and Northwestern Univ.

時間：12月3日（週三）10:00

單位：中國科學院理論物理所

Zoom ID: 832 7630 0290

Passcode: 691240

摘要：

I will present universal relations between the crosssection, which is the primary observable for high energy particle scattering, and entanglement entropy, which quantifies the quantumness of the process. A careful formulation of incoming wave packets is essential to: seattering with no initial entanglement, uncover these relations. We show that for 2-particle seattering with no initial entanglement, the entanglement entropy for elastic final states is the elastic cross section in the unit of the transverse size for the initial wave packets, which can be alternatively interpreted as the elastic seattering probability, This statement does not depend on details of the local dynamies, and is valid to all orders in coupling strength, Furthermore, different ways to partition the system of the two particles lead to final state entanglement entropy expressed as different kinds of semi-inclusive elastie cross sections. Our results imply a version of an area law for entanglement entropy ofa two-body system.

報告人簡介：

Dr Zhewei Yin obtained his BSc degree in 2015 at Peking University, China, and his PhD degree in 2020 at Northwestern University, USA. He then became a postdoctoral researcher at Uppsala University, Sweden, after which he has been holding a joint appointment as a postdoctoral fellow at Northwestern University and Argonne National Laboratory, USA. He works in the field of theoretical high energy physics, with a focus on discovering new properties and developing modern methods in scattering amplitudes and effective field theories, as well as connecting these formal development to particle phenomenology, gravitational wave physics and quantum information science.

5

報告人：何宇馳，根特大學

時間：12月4日（週三）14:00

單位：清華大學物理系

地點：物理樓W316

摘要：

The investigation of twisted bilayer graphene has opened a “twistronics era”, providing unprecedented tunability for solid-state systems and an excellent platform for strongly correlated quantum phases and their transitions. While twisted bilayer graphene requires involved multi-band descriptions, twisted bilayer transition metal dichalcogenides are simpler. In this talk, I will introduce some of our theoretical works related to recent experimental progress. We studied two cases of twisted bilayer transition metal dichalcogenides: (1) effective triangular systems and (2) effective honeycomb systems. For triangular systems, we predict magnetic orders and spin liquids at half-filling; we study the magnetic orders at the van Hove filling, predicting rich metallic magnetic orders. To gain some understanding of magnetism in the case away from half-filling. We use a cluster construction at 1/3 doping and analyze the competing antiferromagnetic and ferromagnetic exchange interactions from different virtual processes. The model we construct supports antiferromagnetism for intermediate interaction and ferromagnetism at strong interactions.

報告人簡介：

Yuchi He obtained his PhD in the physics department of Carnegie Mellon University, USA in 2020. Before that, he earned his BS from Peking University. He worked as a postdoc at RWTH Aachen University and the University of Oxford. Now he is a postdoc at Ghent University and a visiting researcher at Oxford. His primary research interest is phases and dynamics of strongly correlated quantum many-body systems. One-dimensional and two-dimensional systems are investigated by applying and developing effective theory and tensor network methods.

6

報告人：張向東，北京理工大學

時間：12月4日（週三）15:10

單位：北京大學物理學院

地點：物理樓中樓212

摘要：

連續譜束縛態(BICs)是物理學研究領域的一個重要概念。具有連續譜束縛態的光學系統通常含有超高品質因子的共振模式和動量空間的拓撲性質，使其在超低閾值激光、超敏傳感器以及濾波器等方向具有非常重要的應用前景。最近的研究表明，具有高品質因子的準BICs可在不同的納米結構中被實現。但是，其顯著的色散效應也限制了準BICs在廣角光源下的使用效率。另一方面，最近將轉角自由度引入光子結構的設計，構建光子moiré超晶格受到了人們廣泛關注。Moiré光學結構爲設計弱色散的光子平帶提供了重要的平臺。因此一個重要的問題是：是否可以將moiré物理與BICs相結合，來構建具有平帶效應的新的BIC光子態，使其擁有平帶和BICs的雙重特性？本報告將對這方面的研究進展做介紹。

報告人簡介：

張向東，北京理工大學特聘教授、納米光子學與超精密光電系統北京市重點實驗室主任。科技部國家重點研發計劃首席科學家，2008年入選國家傑出青年科學基金支持計劃。長期從事光子晶體和低維納米結構的物理特性及其應用研究，探討利用人工微結構調控經典和量子光場，取得了多項創新成果。在國內外核心期刊上發表論文300餘篇，研究成果曾被Physics Web、Phys. World、ScienceNews等專門報道。

7

報告人：Lingyu Wang，格羅寧根大學

時間：12月5日（週四）15:30

單位：北京大學物理學院

地點：KIAA-auditorium

摘要：

The evolution of massive galaxies is important for understanding key physical processes such as AGN feedback in galaxy formation and evolution. In a cosmological context, statistical properties of this population such as their abundance could also provide an interesting diagnostic test. There is mounting evidence that our knowledge of the galaxy stellar mass function at the high mass end is incomplete, and may even miss the dominant population of the very massive galaxies. To achieve an unbiased census of massive galaxies particularly in the early Universe, it is imperative to account for the dust-obscured star-formation galaxies, which are most easily observed in the far-infrared and sub-millimetre. I will present our efforts and results in tracing this elusive population, their physical properties and triggering mechanisms, by employing a tripod approach of state-of-the-art galaxy surveys, cosmological simulations and artificial intelligence techniques. I will conclude by summarising our main conclusions so far, future outlook and also challenges therein.

報告人簡介：

I obtained B.S. in Physics from Zhejiang University in 2005 and Ph.D. in astrophysics from Imperial Collage London in the UK in 2009. I held post-doctoral research fellowships at the University of Sussex and University of Durham in the UK from 2009 to 2015. In 2015, I was appointed as scientist (tenure track and later tenured) at SRON Netherlands Institute for Space Research and assistant professor at the University of Groningen in the Netherlands. I was promoted to senior scientist in 2021 and associate professor in 2024. My research focuses on statistical galaxy evolution studies in diverse environment across cosmic time and how galaxy evolution connects to the underlying cosmological framework. For more than a decade, I have worked extensively on large multi-wavelength photometric and spectroscopic extragalactic galaxy surveys from the local to the early Universe (such as Herschel, GAMA, LOFAR and Euclid), consistent comparisons with state-of-the-art theoretical models and simulations of galaxy formation and evolution, and applications of machine learning (in particular deep learning) methods. In particular, I focus on investigating the two main physical processes driving galaxy evolution, i.e., star formation and accretion onto supermassive black holes and feedback, using multiple observational probes and test galaxy populations (from field galaxies to galaxy clusters). Over the past decade, I have won various individual and team research grants for my work. I have also served on various international panels and committees, in particular I served as a Topical Team member for the European Space Agency (ESA) Voyage 2050 Programme which sets out priorities in the ESA science mission themes for the timeframe 2035 - 2050.

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報告人：周興江，中國科學院物理研究所

時間：12月5日（週四）16:00

單位：清華大學物理系

地點：理學院鄭裕彤大講堂

摘要：

The superconductivity mechanism in high temperature superconductors remains a prominent and challenging issue in condensed matter physics. Angle-resolved photoemission spectroscopy (ARPES) plays a key role in probing the electronic structure, many-body effect and superconducting gap structure of these superconductors. In this talk, I will report our recent laser-based ARPES studies of the cuprate superconductors, iron-based superconductors and newly discovered nickel-based superconductors. We developed a new approach that makes ARPES able to measure not only the superconducting gap size but also the gap sign. We determined that the pairing symmetry is of the nodal s+-(G-M) type in iron-based superconductor KFe2As2 which has only hole pockets. We found ubiquitous coexisting electron couplings with both the 40 meV and 70 meV modes in cuprate superconductors. We revealed the electronic origin of high-Tc maximization in trilayer cuprate superconductors. We resolved the electronic structures of La3Ni2O7 and found orbital-dependent electron correlations. These results provide key insights in understanding superconductivity mechanism and also pave a way to further enhance Tc in these high temperature superconductors.

報告人簡介：

周興江，中國科學院物理研究所研究員。1988年清華大學學士。1990年清華大學碩士，1994年中國科學院物理研究所博士。1995-1997年德國斯圖加特馬普固體研究所洪堡學者，1997-2006年爲美國斯坦福大學物理學者兼美國勞侖斯Berkeley國家實驗室先進光源束線科學家，2004年入選中國科學院百人計劃，2009-2022年任超導國家重點實驗室主任。長期從事凝聚態物理實驗研究，自主研製系列真空紫外激光角分辨光電子能譜儀，在高溫超導體和其它量子材料的研究中做出了重要工作。發表SCI論文270多篇，論文被引用13000餘次。2003年獲美國Berkeley國家實驗室的 David A. Shirley“傑出科學成就”獎，2005年獲國家級人才基金資助, 2008年獲首屆周光召基金會“傑出青年基礎科學獎”, 2009年獲中國物理學會“胡剛復物理獎”， 2013 年獲全球華人物理和天文學會“亞洲成就獎”， 2015 年獲國家自然科學二等獎， 2015 年獲第三世界科學院TWAS 物理獎，2016 年入選美國物理學會會士。

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報告人：馬傑，上海交通大學物理與天文學院

時間：12月6日（週五）15:00

單位：清華大學物理系

地點：理科樓B315

摘要：

在強關聯阻挫體系中，複雜的自旋、電子、晶格和軌道相互作用常常會導致低能態的宏觀簡併，誘導出一系列新奇的物理特性。當磁矩較小（S=1/2或1）時，這種簡併態極易受到熱漲落、量子漲落等影響，在極低溫、高磁場、強壓力等極端條件下被進一步調控，甚至產生新物態，例如量子自旋液體態，磁化平臺相等等。目前，量子自旋液體材料主要分爲基於強幾何阻挫的共振價鍵體系和基於六角蜂巢晶格上的Kitaev體系。前者的典型代表爲三角晶格、籠目晶格等，但是被哈密頓量不能嚴格求解所限制。Kitaev模型則是起源於二維蜂窩狀晶格，六個頂點上的磁性離子與最近鄰離子沿不同晶格方向存在強各向異性的類Ising相互作用，即Kitaev相互作用。與起源於自旋排列和晶格對稱性不相容誘導的幾何阻挫不同，Kitaev模型中單個格點的自旋由於具有鍵依賴性，其本身就存在阻挫。另外，Kitaev模型的基態可嚴格求解，對研究量子效應、低能分數化激發等具有頗高的研究價值。我們主要利用彈性和非彈性中子散射技術對三角、蜂巢及Shastry-Sutherland等二維晶格氧化物的量子自旋液體行爲開展探索，併力圖對極低溫、強磁場誘導出的各相開展調控。

報告人簡介：

馬傑，上海交通大學物理與天文學院教授。2003年本科畢業於中國科學技術大學；2010年博士畢業於美國衣阿華州立大學；2010年至2016年在美國橡樹嶺國家實驗室/田納西大學開展博士後工作。主要從事凝聚態物理實驗研究方面的工作，在生長樣品的同時，運用中子散射、繆子自旋弛豫/旋轉及同步輻射X光技術對強關聯材料的晶體/磁結構及相關動力學譜進行研究，探討這類材料在極低溫、強磁場、高壓強等極端條件下的電子、磁子、聲子和軌道等相互作用及其導致的諸如電荷有序、軌道晶格耦合、電聲耦合等新奇量子效應，並對這些奇異物性開展調控。

封面圖片來源：https://zhuanlan.zhihu.com/p/513360802

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