金属基催化材料面临的挑战与机遇 | 本周物理学讲座
报告人：蒋青，吉林大学
时间：12月14日（周五）15:00
单位：中科院物理研究所
地点：M楼253会议室
本次报告将首先回顾催化科学一百多年的发展历程，阐述金属基催化剂/催化材料的发展现状及背景。报告人结合自身研究提出了材料科学研究催化材料的优势，并介绍对未来的贡献。
2Topology from chaos: quantum Hall physics, Haldane conjecture and beyond
报告人：田矗舜，中科院理论物理所
时间：12月11日（周二）12:00
单位：中科院理论物理所
地点：理论物理所322报告厅
Chaotic and topological phenomena have totally opposite characteristics: the former/latter are extremely sensitive to/robust against the change in system's details (e.g., the parameters of the Hamiltonian, the initial conditions, etc.). Thus they are commonly considered not to be compatible. In this talk, I will show how, by introducing a spin degree of freedom to the canonical model of chaotic dynamics, the so-called quantum kicked rotor (QKR), which is simply a particle moving on a ring and subjected to pulsed external force, rich dynamical behaviors of topological origin arise. These include, notably, the realization of quantum Hall physics and Haldane conjecture, which occur originally to totally different systems, namely, many-electron systems and quantum antiferromagnetic chains, respectively. I will show how a supersymmetry structure arises from the time-driving nature of QKR, and serves as a seed for a wealth of topological phenomena in this chaotic system as simple as being single-particle.
报告人：Tianbo Liu，Jefferson Lab and Duke University
单位：中科院理论物理所
时间：12月12日（周三）10:00
地点：Conference Room 322, ITP main building
We determine the structure of generalized parton distributions from light-front holographic QCD up to a universal reparametrization function w(x), which incorporates Regge behavior at small-x and inclusive counting rules at large-x. A simple ansatz for w(x) which fulfills the physical constraints leads to precise descriptions of both nucleon and pion valence quark distribution functions. The analytic structure provides a nontrivial connection with hadron spectrum. Keeping the holographic structure, we can unambiguously introduce quark masses, preserving the harding scattering counting rule at large-Q and the inclusive counting rule at large-x. Within the light-front holographic framework, we predict the nucleon strange quark form factor and the asymmetric strange sea distribution up to a normalization factor. Together with lattice QCD data, we derive a lower limit on the intrinsic strange sea of the nucleon.
报告人：王轲，Tsinghua University
时间：12月12日（周三）10:00
单位：中科院物理研究所
地点：M238会议室
Discovery of topological materials has sparked a worldwide interest to harness the topological properties of quantum matter, with important applications in dissipationless electronics and fault-tolerant quantum computing. One prime example is WTe2, which is a layered semimetal that crystallizes in a unique structure where the emergence of massless Weyl fermions in this system is sensitive to atomic-scale lattice distortions. In this talk, I will discuss the topological physics of WTe2, and show that its topological invariants are highly tunable by means of interlayer shear strain, as crystallographically measured using relativistic electron diffraction. We will discuss how ultrashort pulses of terahertz (THz) electromagnetic field can be used to drive the shear mode which in turn serves as an ultrafast, energy-efficient means to induce more robust, well-separated Weyl points or to annihilate all Weyl points of opposite chirality. These results define new methods for ultrafast manipulation of the topological properties in 2D materials that can operate at THz frequencies.
报告人：Manqi RUAN,IHEP CAS
时间：12月12日（周三）10:30
单位：北京航空航天大学
地点：Main Building, 513
The Circular Electron Positron Collider (CEPC), aproposed collider facility with main ring circumference of 100km, is expectedto play a leading role in the particle physics exploration in the next fewdecades. In its nominal design, the CEPC will be operated at center of massenergies from 91 GeV to 240 GeV, and produces 1 Million Higgs bosons, 100Million W bosons, and almost 1 Tera Z bosons in 10 years operation. Giving theextremely clean collision environment of the electron positron collider, CEPC canboost the precisions on Higgs properties by one order of magnitude with respectto the ultimate precision of the HL-LHC, improve the current precision on EWmeasurement by 1-2 orders of magnitudes. Meanwhile, the CEPC also serves as asuperb factory of quarks, leptons, which could significantly enhance ourknowledge on Flavor physics, QED, et.al.
In Nov 2018, the CEPC study group releases itsconceptual design report, an important milestone towards the realization ofthis facility. According to this report, this talk will introduce the physicsreach and the performance of the baseline CEPC detector.
6Scanning near-field optical microscopy and its applications in condensed matter physics
报告人：Zhiwen Shi
时间：12月12日（周三）16:00
单位：北京大学
地点：Room W563, Physics Buildin
Scanning near-field optical microscopy (SNOM), is a microscopy technique for nanostructure investigation that breaks the far field optical resolution limit by exploiting the properties of evanescent waves. Basically, it is a combination of laser and atomic force microscope (AFM), where light is focused onto the apex of a metal-coated AFM tip. The near-field at the tip apex is strongly enhanced, leading to a strong local interaction of light with material underneath the tip. Optical image and spectroscopy with spatial resolution of ~10nm can be achieved, providing the capability to explore light-matter interaction at nanometer scale. In this talk, I will first briefly introduce the SNOM technique, and then talk about a few examples of exploring novel optical phenomena in low-dimensional materials with SNOM.
7Preliminary Study of Three Bosons System in the Finite Volume
报告人：Jia-Jun Wu
时间：12月13日（周四）10:00
单位：北京航空航天大学
地点：Room 316
The three-particle quantization condition is partially diagonalized in the center-of-mass frame by using cubic symmetry on the lattice. By using the Bethe-Salpeter equation for particle-dimer scattering, we expand it in the basis functions of different irreducible representations of the octahedral group. Through one toy model, we show that this method can extract the energy eigenvalues in terms of bound and scattering states in the finite volume.Furthermore, we prove that the energy shift in the finite volume upto L^{-6} is cutoff independent.
8Machine learning the quantum Hall effect
报告人：Xin Wan
时间：12月13日（周四）10:00
单位：北京大学
地点：Room W563, Physics Building
Machine learning has been successfully applied to identify phases and phase transitions in condensed matter systems. In this talk I will discuss its application to quantum Hall systems, focusing on the effect of disorder and guiding center anisotropy. In the first part, I will discuss the effort to quantify critical fluctuations at the plateau transition of an integer quantum Hall system. We develop a finite-size scaling approach based on a convolutional neural network and analyze the critical behavior of the transition. The localization length critical exponent can be obtained from the worst performance of the neural network due to critical fluctuations. In the second part, I will discuss the study of the internal metric of several fractional quantum Hall states with the help of principle component analysis. We show that the response of the metric to interaction anisotropy remains unchanged from 1/3 to 2/5 in the same Jain sequence, but is drastically different at 1/5 filling.
9Cell Press and iScience ：From Life Science to Physical Science
报告人：李健
时间：12月13日（周四）14:00
单位：中科院物理研究所
地点：M249会议室
报告将主要介绍细胞出版社和旗下期刊，特别是近年来科学出版业务的战略调整：从生命科学领域向物理科学领域的拓展，以及新期刊iScience的出版宗旨、标准与流程。最后从编辑的角度出发，提供具体的实用投稿写作技巧，包括Cover Letter的撰写，题目的选取，和推荐审稿人的挑选等。
10Revealing Excitonic Complexes in Monolayer WSe2
报告人：Sufei Shi
时间：12月13日（周四）14:00
单位：北京大学
地点：Room W563, Physics Building
Single layer transition metal dichalcogenides (TMDs) represent a new class of atomically thin semiconductors with superior optical and optoelectronic properties. The two-dimensional nature of single-layer TMDs results in reduced screening and enhanced Coulomb interaction, giving rise to excitonic complexes such as exciton, trion, and biexciton with binding energy orders of magnitude larger than that of conventional semiconductors such as GaAs. The excitonic complexes also possess valley degree of freedom and can be accessed selectively through circularly polarized light. Here we show that by encapsulating the monolayer WSe2 with BN, we can construct devices with high-quality optical spectra which helps to identify fine features of excitonic complexes. The BN encapsulated monolayer WSe2 thus provides an exciting playground for the strong light-matter interaction in 2D.
报告人：Jiangtao Li，Univ. of Michigan
时间：12月13日（周四）14:00
单位：清华大学
地点：蒙民伟科技南楼S727
Circum-galactic medium (CGM) represents multi-phase gases and other matters [e.g., cosmic rays (CRs), magnetic field, dust, etc.] beyond the galactic disk and bulge, but typically within the virial radius of their dark matter halos. This multi-phase CGM plays a key role in the co-evolution of galaxies together with their ecosystem, as a reservoir providing fuels to continue star formation and a depository of energy and metal-enriched materials ejected by various forms of galactic feedback [e.g., from AGN, massive stellar wind, or supernovae (SNe)]. As the most extended and volume filling phase of the CGM, the X-ray emitting hot gas potentially contains a large fraction of the galactic baryon and energy budgets; its origin, spatial distribution, dynamical state, as well as physical and chemical properties are thus critical in determining how the CGM interacts with the galaxies. I will summarize what we have learned about the hot CGM from the existing X-ray observations. I will also present brief prospects on future works on the hot CGM with the existing and forthcoming X-ray missions, as well as the multi-phase CGM observed in multi-wavelength observations and the CGM study at the high redshift universe.
报告人：葛惟昆
时间：12月13日（周四）14:00
单位：清华大学
地点：物理系理科楼C302
作为波动的光波具有偏振特征，作为粒子的光子具有自旋性质。这里介绍关于它们的基本概念和相互关联。
13First Principles Design of Materials for Energy and Optoelectronic Device Applications
报告人：Su-Huai Wei，Beijing Computational Science Research Center
时间：12月13日（周四）16:00
单位：清华大学
地点：理科楼郑裕彤讲堂
Materials design using first-principles techniques is one of the ultimate goals in computational materials science. Recent advances in first-principles electronic structure theory and computing power has enabled us to perform knowledge-based computational design of materials with unique optoelectronic properties that are tuned to specific applications. This approach has now become a vital tool in accelerating scientific discovery of optoelectronic materials. In this talk, selective topics from our recent studies will be discussed to illustrate how computational methods can be used to understand and design functional optoelectronic materials, including solar-electric materials; solar-chemical materials; and transparent conducting materials.
14Holomorphic Hartree-Fock Theory: The Path to Strong Correlation
报告人：Alex Thom，University of Cambridge
时间：12月14日（周五）14:30
单位：中科院物理研究所
地点：D楼210会议室
The mean-field solution to the electronic structure problem is given by the single Slater determinant produced by Hartree-Fock (HF) theory which, in many situations is a reasonably close approximation to the exact solution, lacking only dynamic correlation which can be provided by perturbative or other means. In so-called strongly correlated systems, where there are competing electronic structures, a single mean-field Slater determinant can represent only one of these, and perturbative treatments of correlation break down. The conventional solution to this problem would be a `multi-reference' method, such as Complete Active Space Self-Consistent Field theory, but such methods are far from black-box and generally scale poorly with system size.
We have shown that where there is strong correlation there are in fact many mean-field solutions which act as quasidiabatic states and it is possible to combine them by a Non-Orthogonal Configuration Interaction (NOCI) approach to recover a good description of the system. However, in the region between strong and weak correlation, these multiple solutions coalesce and disappear, making the method unsuitable in such regions. We show that by changing the form of Hartree-Fock to recover a complex-analytic, holomorphic, functional, wherever solutions coalesce, they analytically continue with complex coefficients. These holomorphic Hartree-Fock solutions are smooth and continuous, existing at all molecular geometries and so can be used as a basis for NOCI, recovering the strong correlation with little effort. We show that this approach is effective in some model electron transfer systems.
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