3He超流体、量子自旋液体、晶格 QCD 、 光连续谱束缚态 | 本周物理讲座

1

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

时间：12月3日（周二）10:00

单位：中国科学院物理研究所

地点：怀柔园区X1楼101会议室

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.

报告人简介：

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.

2

报告人：David Smith，法国国家科研中心

时间：12月3日（周二）15:30

单位：北京大学物理学院

地点：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.

报告人简介：

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.

3

报告人：梁剑，华南师范大学

时间：12月3日（周二）15:00

单位：中国科学院高能物理研究所

地点：图书馆楼319会议室

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.

报告人简介：

梁剑，华南师范大学量子物质研究院研究员，博士生导师。2010年本科毕业于南开大学，2015年于中国科学院高能物理研究所获得博士学位，后在美国肯塔基大学从事博士后研究。2020年入职华南师范大学，2022年获得国家优秀青年基金资助。主要从事格点量子色动力学相关的研究工作，致力于从第一性原理出发通过大规模数值模拟研究强子结构与性质。

4

报告人：Zhewei Yin，Argonne and Northwestern Univ.

时间：12月3日（周三）10:00

单位：中国科学院理论物理所

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.

报告人简介：

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

报告人：何宇驰，根特大学

时间：12月4日（周三）14:00

单位：清华大学物理系

地点：物理楼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.

报告人简介：

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

报告人：张向东，北京理工大学

时间：12月4日（周三）15:10

单位：北京大学物理学院

地点：物理楼中楼212

摘要：

连续谱束缚态(BICs)是物理学研究领域的一个重要概念。具有连续谱束缚态的光学系统通常含有超高品质因子的共振模式和动量空间的拓扑性质，使其在超低阈值激光、超敏传感器以及滤波器等方向具有非常重要的应用前景。最近的研究表明，具有高品质因子的准BICs可在不同的纳米结构中被实现。但是，其显著的色散效应也限制了准BICs在广角光源下的使用效率。另一方面，最近将转角自由度引入光子结构的设计，构建光子moiré超晶格受到了人们广泛关注。Moiré光学结构为设计弱色散的光子平带提供了重要的平台。因此一个重要的问题是：是否可以将moiré物理与BICs相结合，来构建具有平带效应的新的BIC光子态，使其拥有平带和BICs的双重特性？本报告将对这方面的研究进展做介绍。

报告人简介：

张向东，北京理工大学特聘教授、纳米光子学与超精密光电系统北京市重点实验室主任。科技部国家重点研发计划首席科学家，2008年入选国家杰出青年科学基金支持计划。长期从事光子晶体和低维纳米结构的物理特性及其应用研究，探讨利用人工微结构调控经典和量子光场，取得了多项创新成果。在国内外核心期刊上发表论文300余篇，研究成果曾被Physics Web、Phys. World、ScienceNews等专门报道。

7

报告人：Lingyu Wang，格罗宁根大学

时间：12月5日（周四）15:30

单位：北京大学物理学院

地点：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.

报告人简介：

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.

8

报告人：周兴江，中国科学院物理研究所

时间：12月5日（周四）16:00

单位：清华大学物理系

地点：理学院郑裕彤大讲堂

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.

报告人简介：

周兴江，中国科学院物理研究所研究员。1988年清华大学学士。1990年清华大学硕士，1994年中国科学院物理研究所博士。1995-1997年德国斯图加特马普固体研究所洪堡学者，1997-2006年为美国斯坦福大学物理学者兼美国劳仑斯Berkeley国家实验室先进光源束线科学家，2004年入选中国科学院百人计划，2009-2022年任超导国家重点实验室主任。长期从事凝聚态物理实验研究，自主研制系列真空紫外激光角分辨光电子能谱仪，在高温超导体和其它量子材料的研究中做出了重要工作。发表SCI论文270多篇，论文被引用13000余次。2003年获美国Berkeley国家实验室的 David A. Shirley“杰出科学成就”奖，2005年获国家级人才基金资助, 2008年获首届周光召基金会“杰出青年基础科学奖”, 2009年获中国物理学会“胡刚复物理奖”， 2013 年获全球华人物理和天文学会“亚洲成就奖”， 2015 年获国家自然科学二等奖， 2015 年获第三世界科学院TWAS 物理奖，2016 年入选美国物理学会会士。

9

报告人：马杰，上海交通大学物理与天文学院

时间：12月6日（周五）15:00

单位：清华大学物理系

地点：理科楼B315

摘要：

在强关联阻挫体系中，复杂的自旋、电子、晶格和轨道相互作用常常会导致低能态的宏观简并，诱导出一系列新奇的物理特性。当磁矩较小（S=1/2或1）时，这种简并态极易受到热涨落、量子涨落等影响，在极低温、高磁场、强压力等极端条件下被进一步调控，甚至产生新物态，例如量子自旋液体态，磁化平台相等等。目前，量子自旋液体材料主要分为基于强几何阻挫的共振价键体系和基于六角蜂巢晶格上的Kitaev体系。前者的典型代表为三角晶格、笼目晶格等，但是被哈密顿量不能严格求解所限制。Kitaev模型则是起源于二维蜂窝状晶格，六个顶点上的磁性离子与最近邻离子沿不同晶格方向存在强各向异性的类Ising相互作用，即Kitaev相互作用。与起源于自旋排列和晶格对称性不相容诱导的几何阻挫不同，Kitaev模型中单个格点的自旋由于具有键依赖性，其本身就存在阻挫。另外，Kitaev模型的基态可严格求解，对研究量子效应、低能分数化激发等具有颇高的研究价值。我们主要利用弹性和非弹性中子散射技术对三角、蜂巢及Shastry-Sutherland等二维晶格氧化物的量子自旋液体行为开展探索，并力图对极低温、强磁场诱导出的各相开展调控。

报告人简介：

马杰，上海交通大学物理与天文学院教授。2003年本科毕业于中国科学技术大学；2010年博士毕业于美国衣阿华州立大学；2010年至2016年在美国橡树岭国家实验室/田纳西大学开展博士后工作。主要从事凝聚态物理实验研究方面的工作，在生长样品的同时，运用中子散射、缪子自旋弛豫/旋转及同步辐射X光技术对强关联材料的晶体/磁结构及相关动力学谱进行研究，探讨这类材料在极低温、强磁场、高压强等极端条件下的电子、磁子、声子和轨道等相互作用及其导致的诸如电荷有序、轨道晶格耦合、电声耦合等新奇量子效应，并对这些奇异物性开展调控。

封面图片来源：https://zhuanlan.zhihu.com/p/513360802

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