1 A glimpse of RIXS and its applications in quantum materials
报告人:周克瑾,Diamond Light Source, UK
时间:3月7日(周二)10:00
单位:中科院物理所
地点:中科院物理所M236会议室
摘要:
Resonant inelastic X-ray scattering (RIXS) is a photon-in photon-out spectroscopic technique utilizing highly intense and monochromatized X-rays to probe the excitations in materials of interest. By selectively working at the resonant thresholds of an element, collective excitations or ordered states, such as magnons, orbitons, plasmons, phonons, charge-density waves, can be probed in the energy-momentum space. Owing to its high cross-section and focused X-ray beam, RIXS is advantageous in measuring micron-size samples and nanometre-thick films.
Over the last decade, RIXS has flourished because of an order of magnitude increase in its energy resolving power. At Diamond Light Source in the UK, the I21-RIXS beamline delivers an energy resolution of 35 meV at Cu L-edge (930 eV) and 15 meV at Oxygen K-edge (532 eV) with high photon throughput. In this talk, I will introduce the principle of the technique and the recent science cases in quantum materials particularly unconventional high-temperature superconductors.
报告人简介:
报告人:刘佳,北京大学
时间:3月7日(周二)10:00
单位:中科院理论物理所
地点:北楼 322
摘要:
We report on an interesting realization of the QCD axion, with mass in the range O(10) MeV. It has previously been shown that although this scenario is stringently constrained from multiple sources, the model remains viable for a range of parameters that leads to an explanation of the Atomki experiment anomaly. In this article we study in more detail the additional constraints proceeding from recent low energy experiments and study the compatibility of the allowed parameter space with the one leading to consistency of the most recent measurements of the electron anomalous magnetic moment and the fine structure constant. We further provide an ultraviolet completion of this axion variant and show the conditions under which it may lead to the observed quark masses and CKM mixing angles, and remain consistent with experimental constraints on the extended scalar sector appearing in this Standard Model extension. In particular, the decay of the Standard Model-like Higgs boson into two light axions may be relevant and leads to a novel Higgs boson signature that may be searched for at the LHC in the near future.
报告人简介:
报告人:周也铃,国科大杭州高等研究院
时间:3月7日(周二)10:00
单位:中科院理论物理所
地点:南楼6420
摘要:
Topological defects are a class of important concepts in particle cosmology. They are physical objects formed when a fundamental symmetry is spontaneously broken during the cooling of the expanding Universe. Typical topological defects include monopoles, domain walls and cosmic strings. While the first two lead to a serous cosmological problem and should be diluted by inflation, the last one is safe and have some interesting features favoured by theorists. The most important one is that it is a main source to generate cosmic background of stochastic gravitational waves (GWs). An observation of this background in the future will be helpful for us to construct a fundamental particle theory at super-high energy scale. On the other hand, biased domain walls could avoid the cosmological problem and provide another source for GWs. In this paper, I will introduce mechanisms of GWs from topological defects and discuss their connections to fundamental particle theories.
报告人简介:
4 Near Charge Density Wave Instability in Superconductor LaO₀.₅F₀.₅BiS₂ and electron-correlation-induced charge density wave in magnetic kagome FeGe
报告人:万贤纲,南京大学
时间:3月7日(周二)10:00
单位:合肥微尺度物质科学国家研究中心、国际功能材料量子设计中心、中科院强耦合量子材料物理重点实验室、中国科大物理系、科研部
会议链接:https://www.koushare.com/lives/room/697299
摘要:
报告人简介:
报告人:郑浩,上海交通大学
时间:3月7日(周二)10:00
单位:中科院物理所
地点:M楼253
摘要:
1965年,Fulde理论预言,超导体中如果库珀对的动量足够大就可以在超导能隙中产生准粒子,从而导致出一种特殊的费米面。但由于普通超导体库珀对动量足够大时,产生准粒子的同时,库珀对也会破裂而失去超导,因此要观察到 超导费米面实验上非常困难。该预言一直没有被证实。我们将拓扑表面态费米速度极高的独特优点应用到超导研究中来,设计并制备出拓扑绝缘体/超导复合体系,提出了外场调控库伯对动量新方法,最终在实验上实现了超导 “分段费米面”。该工作证实了50多年前理论预言,并发现可以用磁场方向和大小来调节“分段费米面”的形状和大小,还能调控拓扑性,构建新的拓扑超导,并开辟了调控物态的新方法。
报告人简介:
报告人:谭鹏,复旦大学物理学系
时间:3月7日(周二)10:00
单位:中科院物理所
地点:M楼255会议室
摘要:
玻璃转变和结晶分别形成非晶固体(玻璃态)和晶体。尽管如此,结晶和玻璃化在动力学方面密切联系。我们将详细介绍我们在这一领域的研究中取得的一些进展,如结晶过程中的非经典形核路径、玻璃态结晶原理和玻璃态中多层级的弛豫的极限形式,以及界面、尺寸、非平衡效应等因素如何影响结晶和玻璃转变。
报告人简介:
报告人:吴洁强,中国科学院理论物理研究所
时间:3月7日(周二)12:00
单位:中科院理论物理所
地点:南楼6620
摘要:
全息纠缠熵已经提出了15年,并在学界取得了巨大的影响。在这一次的报告中,我会围绕全息纠缠熵介绍一些我认为比较重要的题目,以及一些未来可以进一步研究的问题,具体包括:entanglement wedge nesting及其所需要的能量条件、纠缠熵第一定律的全息描述、JLMS formula、极值曲面在哈密顿系统中的性质等。报告内容以综述为主。
8 First-principles calculations for Dzyaloshinskii-Moriya interaction and its application for the DMI-torque switching of perpendicular magnetization
报告人:杨洪新,南京大学物理学院
时间:3月7日(周二)12:00
单位:江苏省物理学会
会议链接:https://www.koushare.com/lives/room/569762
摘要:
报告人简介:
报告人:Jose Ramon Espinosa,西班牙马德里IFT ( Instituto de Fisica Teorica)
时间:3月7日 (周二) 16:00
单位:中国科学院理论物理研究所
会议链接:https://www.koushare.com/lives/room/567655
摘要:
The calculation of tunneling actions, that control the exponential suppression of the decay of metastable phases (like the unstable electroweak vacuum), can be reformulated as an elementary variational problem in field space. This alternative approach circumvents the use of bounces in Euclidean space by introducing an auxiliary function, a tunneling potential Vt that connects smoothly the metastable and stable phases of the field potential V. The tunneling action is obtained as the integral in field space of an action density that is a simple function of Vt and V and can be considered as a generalization of the thin-wall action to arbitrary potentials. This formalism provides new useful handles for the theoretical understanding of different features of vacuum decay, can be easily extended to include gravitational effects in an elegant way and has a number of interesting properties and applications that I will discuss.
报告人简介:
Jose Ramon Espinosa is a full professor of IFT of Madrid in Spain and now is a visiting professor at CERN. He obtained his PhD in 1994 working on Particle Physics beyond the Standard Model at IEM (CSIC, Madrid) under the supervision of Mariano Quirós. After postdoctoral stays at DESY (Hamburg, Germany), University of Pennsylvania (Philadelphia, USA) and CERN (Geneva, Switzerland), from 1999 to 2008 he joined IMAFF (CSIC, Madrid) and then IFT-UAM/CSIC (Madrid) with a permanent position. From 2008 to 2018 he joined ICREA as Research Professor to work at IFAE. Since 2019 he become a member of IFT, Madrid. He is a world-leading particle physicist in BSM phenomenology and cosmology. He has published over 100 papers with over 17000 citations. Recently, he has discovered a new formalism for quantum tunneling in field theory.
10 Novel Orbital Physics – Unconventional Bose-Einstein Condensation, and itinerant Ferromagnetism in optical lattices
报告人:Congjun WU, Westlake University
时间:3月9日(周四)10:30
单位:南方科技大学物理系
会议链接:https://www.koushare.com/lives/room/278537
摘要:
Orbital is a degree of freedom independent of charge and spin. It plays an important role in physical properties of transition-metal-oxides. The recent developments of cold atom systems in optical lattices have opened up an opportunity to study novel features of orbital physics that are not easily accessible in solid state systems. We predicted that cold bosons, when pumped into high orbital bands of optical lattices, exhibit a class of novel superfluid states spontaneously breaking time-reversal symmetry. In analogy to unconventional superconductivity, their complex-valued condensate wavefunctions possess unconventional symmetries beyond the scope of “no-node” theorem for most states of bosons. This class of unconventional Bose-Einstein condensations have been experimentally realized by a few prominent experimental groups. On the other hand, itinerant ferromagnetism (FM), i.e., FM based on Fermi surfaces instabilities of mobile electrons (fermions), is a hard-core problem of strong correlation physics. The well-known Stoner criterion overestimates the FM tendency by neglecting correlation effects. Furthermore, the paramagnetic metal phase above the Curie temperature, i.e., the Curie-Weiss metal state, is a long-standing challenge. It exhibits a dichotomic nature: The spin channel is incoherent, i.e., local moment-like, while the charge channel remains coherent. In spite of these difficulties, we proved a series of theorems setting up the ground state FM phase in the p-orbital bands. The Curie-Weiss metal phase and the critical scalings of the FM transitions are studied via the sign-problem free quantum Monte-Carlo simulations at high numerical precisions. These results also shed light on the mechanism of itinerant FM and Curie-Weise metal in solid state orbital systems.
报告人简介:
Congjun Wu received his Ph.D. in physics from Stanford University in 2005, and did his postdoctoral research at the Kavli Institute for Theoretical Physics, University of California, Santa Barbara, from 2005 to 2007. He became an Assistant Professor in the Department of Physics at the University of California, San Diego in 2007, an Associate Professor in 2011, and a Professor in 2017. In 2021, he became a Chair Professor at School of Science, Westlake University. He was selected as a New Cornerstone Investigator in 2023, elected to a Fellow of American Physical Society in 2018, and awarded the Sloan Research fellowship in 2008. His research interests are exploring new states of matter and reveling their organizing principles, including quantum magnetism, superconductivity, topological states, mathematical physics, and the numerical method of quantum Monte Carlo simulations.
报告人:Wei Ji(季伟),Helmholtz Institute Mainz
时间:3月9日(周四)14:00
单位:清华大学物理系
地点:理科楼C109
摘要:
Tabletop precision measurements provide powerful tools to search for new physics beyond the standard model, such as dark matter and exotic spin-dependent interactions (5th force). The exotic spin-dependent interaction may be mediated by new ultralight bosons, such as axion or Z', which are also proposed as dark matter candidates. In this talk, I will introduce ultra-high sensitivity alkali-noble gas atomic magnetometers and their application in searching for exotic spin-dependent force. Our recent experiments set stringent limits on different terms of exotic forces between electron-electron, neutron-neutron, or electron-proton. These experimental results represent orders of magnitude improvement by other lab-based experiments. For the Z' boson-mediated term, our result can surpass the limits set by astrophysical methods.
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