多体微扰理论、二次谐波生成、偶极阿贝尔任意子、非线性非厄米奇异点 | 本周物理讲座

学术 2024-10-29 09:31 北京

1 From Chiral Electronics to Mottness in Momentum-Space

报告人：Dr. Niels B.M. Schröter，Max Planck Institute of Microstructure Physics

时间：10月29日（周二）10:00

单位：清华大学物理系

地点：理科楼C302

摘要：

The term chirality is derived from the Greek word for ‘hand’ χειρ (kheir)and describes objects that are distinct from their mirror image. It is long known that chirality plays a crucial role in nature, providing powerful functionality to chiral molecules in living organisms. By extending this concept from the molecular to the solid state, my group aims to uncover new chirality-enabled phenomena that could form the basis for new technologies.The focus of my talk will be on chiral topological semimetals, a new class of quantum materials at the intersection of structural and electronic chirality. The first examples of this material class were discovered in 2019, and since then, it has been demonstrated that they can host new fermionic quasiparticles without analogue in high-energy physics, which carry large and controllable topological charges. I will present new results beyond these initial works and demonstrate that these materials realize an isotropic Weyl-type parallel spin-momentum locking that can be considered the natural counterpart of Rashba spin-orbit coupling. Moreover, I will present fingerprints of controllable orbital angular momentum monopoles in these materials, which could be exploited in memory devices for field-free switching of magnets with perpendicular magnetic anisotropy.Time permitting, I will also present our work on elucidating the origin of the magnetic field-induced and field-free Josephson diode effect. For the latter, we identify a momentum-resolved signature of Mottness that allows us to distinguish band- from unconventional Mott-insulators with an even number of electrons.

报告人简介：

Since 2021, Dr. Niels B. M. Schröter has been leading an independent Max Planck Research Group at the Max Planck Institute of Microstructure Physics in Halle, Germany. He earned his DPhil in Physics from the University of Oxford in 2018, followed by postdoctoral research at the Paul Scherrer Institute in Switzerland. He is the recipient of the 2021 IBM Condensed Matter Physics Award for his discovery of chiral topological semimetals and holds an ERC Starting Grant to further explore this novel material class. His research spans the spectroscopy and synthesis of quantum materials, with a particular focus on structurally chiral materials that exhibit unique chiral electronic, spin, and orbital textures, offering potential applications in next-generation technologies. From 2025, he will be a full Professor (W3) of Experimental Physics at the Martin-Luther University Halle-Wittenberg, while still maintaining his research lab at the Max Planck Institute. He is currently recruiting prospective graduate students and postdocs to work on his ERC funded research. For more information, please visit www.schroeterlab.org.

2 Ab-initio description of quantum phases and their dynamics far from equilibrium

报告人：E.K.U. Gross，Hebrew University of Jerusalem

时间：10月29日（周二）10:00

单位：中国科学院物理所

报告地点：M楼236会议室

腾讯会议：942-399-323

会议密码：241029

摘要：

The basic idea of “functional theories” is to describe nature in terms of simple reduced quantities rather than the full many-body wave function. Prominent examples of functional theories are density-functional theory as well as Green-function-functional theory (better known as many-body perturbation theory). After an overview of the basic concepts of standard ground-state density functional theory (DFT) as well as time-dependent DFT (TDDFT), the description of quantum phases, such as magnetism and superconductivity within these frameworks will be addressed. The idea is to include the order parameter describing the respective quantum phases or the corresponding Green function explicitly in the formalism. This can be done both in the static case and in systems driven far from equilibrium. As a real-world example, the ultrafast laser-induced spin dynamics in magnetic materials will be simulated and first steps toward the analogous treatment of superconductors driven by external fields will be presented.

报告人简介：

Eberhard Gross received his PhD in Physics in 1980 at the Goethe University in Frankfurt, Germany. After a postdoctoral stay at the same university, he joined the group of Walter Kohn at the University of California, Santa Barbara, first as a postdoc, then as a Heisenberg fellow. In 1990, he became Professor of Physics at the University of Wuerzburg, Germany. From 2001 he had the Chair of Theoretical Physics at the Free University of Berlin, and from 2009 to 2019 he was Director of the Max Planck Institute of Microstructure Physics in Halle, Germany. Since 2017, he is Professor of Chemistry at the Hebrew University of Jerusalem, Israel. Together with Erich Runge, he laid the foundation of time-dependent density functional theory. He furthermore developed the Ensemble DFT of excited states, and an ab-initio theory of phonon-driven superconductivity. In recent years, he developed the exact factorization, a novel methodology describing all aspects of non-adiabatic chemical dynamics, in particular electronic decoherence and the molecular Berry phase. His work has been recognized with several prizes and awards, including the 2016 Bernie Alder CECAM prize, the 2016 Tsungming Tu prize in Taipei, the Schlumberger Award with medal, and the CMOA senior medal. He is a member of the International Academy of Quantum Molecular Science, a Fellow of the American Physical Society and a Mercator Fellow of the German Science Foundation (DFG).

3 非线性非厄米奇异点

报告人：白凯，武汉大学博士后

时间：10月29日（周二）14:00

单位：中国科学院物理所

腾讯会议：631-544-345

会议密码：1029

摘要：

奇异点（EP)是一类特殊的能谱奇点，在该点处，两个或多个本征模式聚合，其本征矢量因聚合而变得平行，从而致使哈密顿量的本征基的完备性丢失。EP 附近的奇特物理性质带来了各种新奇应用, 如信号放大、激光模式分辨、微小信号探测、量子传感、能量转移、光子芯片、单向激光、量子控制、模式转换等。然而随着参数接近EP ，由于本征矢量趋于平行，系统噪音显著增大，这将极大地阻碍上述应用的实现。为此，我们提出了非线性奇异点(NEP)，并且在电路系统中对其进行了观测。其在保持线性 EP 的基本特性的同时，在动力学过程中恢复了有效哈密顿量的本征基的完备性，从根本上解决了因本征基矢聚合而引起的噪音发散问题。

报告人简介：

白凯博士于2015年获得兰州大学学士学位，2019年获得兰州大学硕士学位（师从罗洪刚教授和安钧鸿教授），2023年获得武汉大学博士学位（师从肖孟教授），2023-至今在武汉大学刘正猷教授课题组从事博士后工作。近年来以第一作者身份在Phys. Rev. Lett. (4篇)、Natl. Sci. Rev.等国际知名期刊发表相关论文6篇上发表论文。2023年至今，主持国家自然科学基金青年项目，博士后创新人才支持计划，中国博士后面上资助科研项目3项。

4 Dipolar Abelian anyons

报告人：Professor Jung Hoon Han，Sungkyunkwan University, South Korea

时间：10月29日（周二）16:00

单位：清华大学物理系

地点：理科楼C302

摘要：

Properties of Abelian anyons are well-known and can be encoded as Abelian Chern-Simons or BF field theories. Lattice realization of the latter is the famous toric code. Recently, our group has explored a variant of the toric code called the rank-2 toric code (R2TC), where the Abelian anyon excitations exhibit dipolar constraint, dipolar braiding, and are described by dipolar BF theory. In this talk, I introduce the model and explain how it came about, then move on to describe its basic properties such as the ground state degeneracy and associated Wilson operators, topological entanglement entropy, braiding statistics, and finally encode them in field-theoretic form. I conclude with a comment on how the various features can be understood in the framework of symmetry-enriched topological phase. This work has been done in collaboration with Daniel Bulmash, Yun-Tak Oh, Jintae Kim, Hyunyong Lee, Salvatore Pace, Yizhi You.

报告人简介：

Jung Hoon Han leads the Theory of Information & Matter Group at Sungkyunkwan University in Suwon, South Korea. He earned his BSc in physics at Seoul National University, South Korea, in 1991 and his PhD in physics at the University of Washington in 1997 under David Thouless. His research focuses on understanding complex quantum behavior in real materials. More recently, he has worked on developing quantum models with dipole symmetry.

5 New Higgses at the electroweak scale

报告人：Andreas Crivellin，Physik-Institut, Universitat Zurich, and Paul Scherrer Institut

时间：10月30日（周三）15:00

单位：中国科学院理论物理所

地点：北楼322

Zoom ID: 832 7630 0290

Passcode: 691240

摘要：

Statistically significant di-photon excess at 95 GeV(~3sigma) and 152 GeV (>4sigma) have been observed, Furthermore, strong tensions exist between the SM predictions and measurements of W and top-like signatures at the LHC. I discuss the status of these anomalies, and how they can be related via new Higgses at the electroweak scale.

报告人简介：

Andreas Crivellin is a SNSF Professor at University of Zurich and Paul Scherrer Institute, Switzerland in 2019, He received his Ph.D. from Karlsruhe institute of Technology in 2013. After that, he was a postdoc at University of Bern and CERN before joining the SNSF Professorship. Also, he had a Scientific Associateship at CERN during 2020-2021. His main research area is physics beyond the Standard Model, with a particular focus on the flavour anomalies and the LHC anomalies. He has 110+ peer reviewed articles with 10 authors or less, including 16 of them published in Physical Review Letters. He is currently interested in growing evidences for new scalars at the electroweak scale.

6 Second harmonic generation: a symmetry probe for 2D materials

报告人：吴施伟，复旦大学

时间：10月30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：

Atomically thin two dimensional materials such as graphene, transition metal dichalcogenide and chromium trihalide monolayers have recently spurred a great of interests due to their unique mechanic, electronic, optical and magnetic properties. And often these properties could be greatly tuned by external stimuli such as electric, magnetic and force field. Individual member in this class of 2D materials is also characteristic in term of different symmetries. Moreover, the symmetries could also be tuned, depending on how monolayers are stacked on one another. These variations in symmetry have given rise to even richer properties among different 2D materials and their homo-/hetero-structures. Therefore, they provide a new playground for nonlinear optics, namely second harmonic generation, because of its sensitivity to symmetries. Vice versa, second harmonic generation becomes a powerful technique to study 2D materials. In this talk, I will present some of our recent results on 2D materials.

报告人简介：

Dr Shiwei Wu is currently Xie Xide Chair Professor of Physics and the director of Key Laboratory of Micro and Nano Photonic Structures (MOE) at Fudan University. His research focuses on the optical microscopy and spectroscopy of low-dimensional materials, with the effort of developing the novel experimental methods to solve cutting-edge problems in condensed matter physics. He obtained his bachelor degree from Fudan University in 2001 and his PhD degree from University of California, Irvine in 2007. Before joining the department of physics at Fudan in 2011, he worked in the Molecular Foundry of Lawrence Berkeley National Laboratory as a postdoc fellow.

7 Current and future upgrades of ESO/VLTI and opportunities for supermassive black hole studies

报告人：Jinyi Shangguan，北京大学

时间：10月31日（周四）15:30

单位：北京大学物理学院

地点：KIAA-auditorium

摘要：

The GRAVITY instrument on the European Southern Observatory's Very Large Telescope Interferometer (VLTI) has brought significant advancements to infrared interferometry with its high spatial resolution and sensitivity. The ongoing GRAVITY+ project will equip the VLTI with wide-angle phase reference delay lines, state-of-the-art adaptive optics, improved vibration control, and other upgrades. These enhancements will not only greatly improve GRAVITY's performance but also reshape the entire VLTI system. In this talk, I will provide an overview of GRAVITY's technology and scientific achievements, highlight the recent progress of GRAVITY+, and discuss future opportunities for extragalactic supermassive black hole (SMBH) studies. GRAVITY+ will enable accurate measurements of SMBH masses and broad-line region structures for a large sample of AGNs at both low and high redshifts. Additionally, multiwavelength synergetic observations will provide critical data for investigating SMBH accretion, AGN feedback, and the search for SMBH binaries. I will conclude by discussing the prospects for the next-generation VLTI.

报告人简介：

Jinyi Shangguan is now an assistant professor at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University. He got his Ph.D. in 2018 at Peking University, with studies of the interstellar medium of quasar host galaxies. Hereafter he joined the Infrared Group of Max-Planck Institute for Extraterrestrial Physics, and has been working on observations and data analyses of the VLTI/GRAVITY interferometer. He uses GRAVITY to study the broad-line region dynamics and hot dust continuum of active galactic nuclei together with multiwavelength observations from other instruments. He joined KIAA in October 2024.

8 The Statistical Physics of Optimal Transport

报告人：Prof. Henri Orland，Université Paris-Saclay

时间：10月31日（周四）10:00

单位：中国科学院理论物理所

地点：北楼322

摘要：

We show how the Optimal Transport problem can be recast in the framework of statistical physics and studied at finite temperature. This allows for the implementation of very fast and efficient algorithms and the generalization of the Wasserstein distance to finite temperature. The statistical physics method can be extended to several forms of unbalanced Optimal Transport problems, and to the Gromoy-Wasserstein metric. We show applications to shape recognition as well as to some biological problems. Finally, we discuss some implications to none quilibrium statistical physics.

报告人简介：

Henri Orland is a senior theoretical physicist and former director of the Institut de Physique Théorique, CEA, University of Paris-Saclay. His research interestsencompass quantum many-body theory & nuclear physics, statistical physics of disordered systems, biological systems, and soft condensed matter. He is a member of the American Academy of Arts and Sciences. Orland has written more than 200 research papers published in major journals; he is the author of twobooks, Ouantum Many-Particle Systems with John W. Negele and Molecular Kinetics in Condensed Phases: Theory, Simulation, and Analysis with Ron Elberand Dmitri Makarov.

9 Imaging ferroelastic domain dynamics with nanoscale X-ray diffraction at the MAX IV synchrotron

报告人：Jesper Wallentin，Lund University

时间：10月31日（周四）14:30

单位：中国科学院物理研究所

地点：物理所M253会议室

摘要：

Metal halide perovskites (MHPs) have shown impressive results in solar cells, light emitting devices, and scintillator applications, but basic questions regarding its complex structure are still open. The low symmetry of MHP crystal structures allows the formation of ferroelastic domains, whose ferroelectric nature is debated. Ferroelastic and ferroelectric materials show nanoscale domains with typical sizes ranging from 10 to 1000 nm. Imaging dynamics of ferroic domains require an experimentally challenging combination of high spatial resolution, strain sensitivity and long penetration depth. We have developed nanoscale X-ray diffraction methods to study the dynamics of ferroelastic domains within MHP nanostructures, made available by recent developments in X-ray optics and synchrotron sources. CsPbBr3 nanowires were imaged across the orthorhombic to tetragonal crystal phase transition using in situ temperature-dependent nanofocused scanning X-ray diffraction, with the 60 nm beam at the NanoMAX beamline, MAX IV. The formation of highly organized domain pattern near 80 °C revealed the ferroelastic nature of the domains. To achieve improved temporal resolution, we used the newly developed Full-Field Diffraction X-ray Microscopy technique, available at the ID01 beamline, ESRF, France, to probe the domain evolution at 6 s time resolutions. Twinned ferroelastic domains in single 500 nm CsPbBr3 particles were studied with 3D Bragg coherent x-ray diffraction imaging. These results demonstrate that X-ray methods now offer sufficient spatial resolution to image ferroic domains, allowing for in situ studies of their formation and dynamics in realistic conditions. Finally, I will give an update of the status of the 4th-generation synchrotron MAX IV in Lund, Sweden (https://www.maxiv.lu.se/).

报告人简介：

Jesper Wallentin is Professor at the division for Synchrotron Radiation Research at Lund University, Sweden. He was previously a postdoctoral fellow at the University of Göttingen, Germany. His research concerns the intersection of nanoscience and X-ray science, both developing X-ray methods to investigate nanostructured devices, and developing nanostructured X-ray detectors. His group has a strong collaboration with the Nanomax beamline at MAX IV in Lund, but also visits many other synchrotrons for experiments.

10 Multi-reference many-body perturbation theory

报告人：李振东，北京师范大学

时间：10月31日（周四）15:00

单位：中国科学院物理研究所

地点：M238

摘要：

Standard many-body perturbation theory is the foundation for many computational methods used today such as the GW approximation. However, it is well-known that this perturbation series breaks down in the presence of strong electron correlation. In this talk, I will present some recent progresses towards generalizing standard many-body perturbation theory (MBPT) to the multi-reference case. Specifically, I will introduce a multi-reference generalization of random phase approximation (RPA) and the closely related second-order screened exchange (SOSEX) approximation based on diagrammatic resummation. Proof-of-concept results for typical molecules demonstrate that the resulting MR-RPA and MR-SOSEX successfully resolve the problems of the single-reference variants. This paves the way towards developing more reliable computational methods for strong correlation problems based on diagrammatic resummation.

报告人简介：

李振东，男，北京师范大学化学学院教授。2014年于北京大学获得理学博士学位，2014-2016年为美国普林斯顿⼤学博士后，2016-2018年为美国加州理⼯学院博⼠后。2019年加入北京师范大学化学学院。2020年入选国家海外人才青年项目，同年度获中国化学会唐敖庆理论化学青年奖。主要从事高精度量子化学方法与程序开发、量子计算化学模拟。

11 On 2d conformal field theories

报告人：Prof. Kimyeong Lee，BIMSA

时间：11月1日（周五）15:00

单位：北京大学物理学院

地点：物理学院南楼408

摘要：

In this talk, l would like to summarize our recent works on 2d conformal field theories. We cover Modular linear differential equation for fermionic conformal field theories, Hecke transformations, VOAs related to Intermediate Algebras and E7+1/2, and a bit of Monster Moonshine. In addition, we want to discuss additional challenges in the subject.

报告人简介：

I am a theoretical physicist working on quantum field theory and string theory. l have been educated in South Korea and United States, I worked as postdoctoral fellow and faculty member in US and also in South Korea. Recently l joined BlMSA in quantum field theory and string theory group. My research interests are also on cosmology, black holesparticle phenomenology, geometry, representation theory vertex operator agebras, categorical symmetries, and number theory.

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