从激子迁移与电荷传输调控构建高性能有机太阳能电池 | 本周物理学讲座
报告人：黄辉，中国科学院大学
时间：7月11日（周三）09:30
单位：北京大学
地点：物理楼西楼464室
报告将围绕高性能有机太阳能电池的构建这一主题，从非共价“构象锁”构建高度共平面有机半导体材料和三线态碲吩材料的合成与应用入手，研究有机半导体材料结构与太阳能电池性能的关系。
报告人：Claudio Ricci
时间：7月10日（周二）12:00
单位：北京大学
地点：1st floor meeting room, KIAA
X-ray emission is an ubiquitous property of active galactic nuclei and, being produced within a few gravitational radii from the accreting supermassive black hole, it can provide fundamental information about the characteristics of the accretion flow, and about the structure and geometry of the circumnuclear material.In my talk I will review some of the most recent findings obtained by the BAT AGN Spectroscopic Survey (BASS - www.bass-survey.com), the largest multi-wavelength survey of hard X-ray (>10 keV) selected AGN, with particular emphasis on the properties of the gas and dust located in the inner parsecs of these systems. I will also discuss the first results obtained with a newly developed simulation platform, RefleX, which allows to reproduce absorption and reflection of X-ray radiation by quasi-arbitrary geometries.
3 Atomic-resolution observation of crystal growth in metallic glass nanorods
报告人：Yujun Xie
时间：7月10日（周二）14:00
单位：中科院物理所
地点：D楼210
Crystallization induced microstructure plays a central role in tailoring materials properties, yet our understanding of its formation process is limited due to its complexity. Classical crystallization theories assume that nucleation and growth are separate processes in which thermodynamically unstable clusters fluctuate in the nucleation stage, but do not participate in the later growth. Here, we apply in situ aberration-corrected transmission electron microscopy (TEM) technique to directly observe the crystal growth of metallic glass nanorods at the atomic resolution and test the classical theories. Surprisingly, we show that, at the atomic scale, the isothermal growth rate for a single crystalline phase is asymmetric upon thermal history. This observation is in direct contrast to what would be expected based on classical theories. We further observe that the asymmetric growth rate depends on the diameter of the nanorod. Thus, our in situ TEM observations mark departure from classical theories.
4 Highly magnified stars in lensing clusters and a probe for dark matter substructure
报告人：Liang Dai, IAS
时间：7月10日（周二）14:00
单位：清华大学
地点：蒙民伟科技南楼S727
Observations have uncovered a new type of gravitational lensing phenomenon that can be utilized to address fundamental physics questions: in galaxy cluster strong lensing systems, background galaxies straddle the lensing caustic and stars near the caustic can be individually detectable to optical/IR telescopes (as in the case of a recent detection by the HST) thanks to the extreme magnification. I discuss how we can use caustic-crossing stars to probe small subhalos or other small-scale granularity in the cluster's halo beyond the reach of existing methods, thus constraining the microscopic nature of the dark matter. I also discuss the prospect of this method with the forthcoming JWST or with the next-generation giant ground-based optical/IR telescopes.
5Novel Carbons – From Graphene to Generalized Grphenoid Compounds
报告人：Stefano Leoni，Cardiff University
时间：7月10日（周二）15:30
单位：中科院物理所
地点：M楼830会议室
Research on novel carbon allotropes never loses momentum. This is due to its ability to form tetrahedral sp3 compounds like diamond, as well as planar sp2 graphite. Between those, manifold intermediates are known, from fullerenes to nanotubes, from hyperbolic Schwarzites to carbon foams. While the planar sp2 unit implies layers of merged six-rings, as regular triangles tile the Euclidean plane, this is not necessarily true for structures based on sp3 centers. Diamond consists of adamantane-like cages of fused six-rings in chair conformation. On the other hand 3D structures with planar six-rings and tetrahedral centers seem to be intrinsically a problem, unless there is a certain amount of odd rings in the structure. Combination of odd and even rings is key to hard and transparent carbon materials, while entangling 1D nanotubes in regular pattern produces superior hydrogen storage materials. Dirac fermions appears in single sheet graphene, while electronic properties can be further tuned in few-layers gaphite. In the attempt to expand the catalogue of carbons, we have found novel graphenoid structures, based on sp2 centers, which nonetheless are not planar, i.e. they represent 3D gaphenes. They define a novel class of compounds, very poorly investigated so far, that can be derived from generalized graphite compounds. Along this way, different graphite(s) as well as graphenoid carbons can be obtained, which hosts interesting electronic properties. The chirality of some of them may represent the starting point towards pure carbon 3D Weyl fermion materials, which so far could be realized in exotic materials only. The possibility of experimentally accessing these materials from suitable precursors can be studied by accurate mechanistic investigation based on advanced molecular dynamics techniques, showing details of pressure-induced material formation.
报告人：Philip Willke，IBM Almaden Research Center
时间：7月10日（周二）16:00
单位：清华大学
地点：物理系理科楼C302
In this talk I will present our recent progress in single atom electron spin resonance (ESR) realized in a scanning tunneling microscope (STM) [1,2].In the first part I will show that we can resolve and control the hyperfine interaction of individual atoms by using ESR-STM. Using atom manipulation to move single atoms we find that the hyperfine interaction strongly depends on the binding configuration of the atom as well as the proximity to other magnetic atoms. This allows the extraction of atom- and position-dependent information about the electronic ground state, the state mixing with neighboring atoms as well as properties of the nuclear spin. Thus, the hyperfine spectrum becomes a powerful probe of the chemical environment of individual atoms and nanostructures. In addition, I show that we are able to extend ESR-STM to perform magnetic resonance imaging (MRI) for the first time on individual atoms. Here, we use the magnetic field of the STM tip to shift the Zeeman energy of the atom on the surface and cause spatial variations in the resonance frequency. While this is similar to existing scanning field gradient methods[3,4], our approach exceeds their spatial resolution by one to two orders of magnitude, to achieve ？ngstr？m resolution.Hyperfine interaction of individual titanium atoms. ESR spectra for 48Ti (top, nuclear spin I = 0) 47Ti (middle, I = 5/2) and 49Ti (bottom, I = 7/2). Right panel: STM images of the individual Ti atoms on a MgO surface.
7Interface-Driven Quantum Magnetism in Oxide Heterostructures
报告人：Jiandi Zhang, Louisiana State University
时间：7月10日（周二）16:00
单位：清华大学
地点：物理系理科楼B315
A defining characteristic of complex transition-metal oxides (TMOs) is their vast variety of physical properties, emerging from a complicated competition between multiple energy scales and the close coupling with charge, spin, and lattice degrees of freedom. The chemical and physical complexity, though presenting a formidable challenge in condensed matter physics, offer a fabulous playground for making artificial structures of these materials with new quantum physics of matter.
In this talk, I will introduce our ability in growing high quality thin films with atomically sharp interfaces, as well as powerful tools to characterize their properties down to atomic scale, which allow us to explore unconventional interfaces and search for novel quantum functionality. I will discuss that broken symmetry at interface results in many exciting emergent phenomena: 1) spontaneous magnetization reversal and inverted hysteresis persisting well above room temperature at the interface of La2/3Sr1/3MnO3 (LSMO)/SrTiO3; 2) interface-induced magnetic polar metal phase in BaTiO3/SrRuO3/BaTiO3 (BTO) heterostructure; and 3) Interface-induced multiferroism in BTO/LSMO superlattices. These exciting new properties are closely related to the dramatic modification of structure/chemistry at the interface. Our results open up a conceptually intriguing recipe for developing novel functional ultrathin materials via interface-induced charge-spin-lattice coupling.
报告人：Q. Charles Su，Illinois State University
时间：7月11日（周三）10:00
单位：北京大学
地点：物理楼中楼215
After receiving a Bachelor’s of Science from Nankai University, Dr. Q. Charles Su went to the University of Rochester (USA) for his graduate studies through the CUSPEA scholarship program coordinated by Nobel Laureate T.D. Lee of Columbia University. He worked in the field of theoretical Quantum Optics under the guidance of Andrew Carnegie Professor J.H. Eberly and received his PhD in 1991. He performed his postdoctoral research at the Max-Planck Institute for Quantum Optics in Munich, Germany. Dr. Su began his career in Illinois State’s Physics Department in 1994, has held the University Professor honor since 2011 and the Distinguished Professor honor since 2016. He shared the American Physical Society Prize for Faculty Research in an Undergraduate Institution in 2006 with his colleague (Dr. R. Grobe). As a Cotrell Science Scholar, Dr. Su was awarded the Singular Exceptional Endeavor of Discovery Grant by Research Corporation in 2017. He has been PI or Co-PI on research grants issued by the National Science Foundation, the US Department of Energy, Research Corporation and the National Science Foundation-China with a total of grant funding that exceeds 2.5 million dollars. Dr. Su has published more than 170 research articles, and has been invited to present at numerous conferences and research institutions. He was elected a Fellow of the American Physical Society in 2012.
报告人：Qiang Yuan，PMO
时间：7月11日（周三）12:00
单位：北京大学
地点：KIAA, 1st meeting room
The dark matter particle explorer (DAMPE) is a space-borne high energy cosmic ray and gamma-ray detector dedicated to searching for dark matter indirectly in space. The wide energy range coverage, high energy resolution, and high particle identification capability of DAMPE successfully open a new window for the high energy Universe. Since its launch in the end of 2015, DAMPE has been operated smoothly for more than 2 years in space. Based on the data recorded by DAMPE, we have measured the cosmic ray electron plus positron fluxes with very high precision to about 5 TeV, which may shed new light on the detection of dark matter. In this talk the background of dark matter detection, the DAMPE detector and performance, and the first physical results will be presented.
报告人：Xiaoqin (Elaine) Li，University of Texas Austin
时间：7月11日（周三）15:00
单位：中科院物理所
地点：M楼 253会议室
Fundamental excitations (e.g. plasmons, excitons, phonons and magnons) determine both the equilibrium and non-equilibrium properties of solids such as metals, semiconductors, and magnetic materials. In this talk, I will give a few examples of our recent work on investigating how such fundamental excitations and particularly coupling between different types of excitations can be probed and controlled. In the first example, I will discuss how magnon and phonon non-equilibrium in a magnetic insulator driven by a temperature gradient leads to spin current. In the second example, I will discuss how coupling between excitons and surface plasmon polaritons can be used to sort and route valley polarized excitons in monolayer semiconductors.
报告人：包吉明，University of Houston
时间：7月11日（周三）15:30
单位：北京师范大学
地点：物理楼106
In this talk, I will show you two recent works from my lab. I will first demonstrate the generation of a liquid jet by simply focusing a pulsed laser into water through a glass window. This is a new optofluidics principle that combines photoacoustics with acoustic streaming. Due to small momentum of photons and many other reasons, the transportation or manipulation of matter with lasers has been a great challenge. The key to our laser streaming is a special photoacoustic transducer that can convert a single laser pulse to a multi-cycle ultrasound oscillation, a train of laser pulses can then generate a quasi-continuous ultrasound wave which produces a steady flow as in classical acoustic streaming. In the second part, I will talk about some important but controversial issues in low dimensional Perovskites. Specifically, I will discuss about edge states in Ruddlesden-Popper organic-inorganic perovskites, controversial bandgaps of two-dimensional CsPb2Br5 and zero-dimensional Cs4PbBr6. I will share with you our preliminary results and understandings of these materials.
12Quantum Yang-Mills problem and implications in QCD and Quantum Gravity
报告人：Dmitriy G. Pak，Inst. of Modern Physics, Lanzhou
时间：7月12日（周四）10:00
单位：中科院理论物理所
地点：Conference Room 6420, ITP new building
I give a short review on principal problems and conceptual issues of the Millennium problem of quantum Yang-Mills theory. Recently a significant progress in formulation of a microscopic theory of the vacuum of SU(3) Yang-Mills theory and understanding the origin of color confinement in quantum chromodynamics (QCD) has been achieved. In particular, a long-standing, key problem of existence of a stable vacuum has been resolved. This revelas the microscopic vacuum structure which manifests an exact Abelian projection conjectured by 't Hooft in 1981.
A brief outline of ways towards full resolution of the quantum Yang-Mills problem and possible implications in quantum gravity and DM/DE problem are discussed.
报告人：Jiming Bao
时间：7月12日（周四）10:00
单位：中科院物理所
地点：M楼253会议室
I will show you two recent works from my lab. I will first demonstrate the generation of a liquid jet by simply focusing a pulsed laser into water through a glass window. This is a new optofluidics principle that combines photoacoustics with acoustic streaming. Due to small momentum of photons and many other reasons, the transportation or manipulation of matter with lasers has been a great challenge. The key to our laser streaming is a special photoacoustic transducer that can convert a single laser pulse to a multi-cycle ultrasound oscillation, a train of laser pulses can then generate a quasi-continuous ultrasound wave which produces a steady flow as in classical acoustic streaming. In the second part, I will talk about some important but controversial issues in low dimensional Perovskites. Specifically, I will discuss about edge states in Ruddlesden-Popper organic-inorganic perovskites, controversial bandgaps of two-dimensional CsPb2Br5 and zero-dimensional Cs4PbBr6. I will share with you our preliminary results and understandings of these materials.
报告人：Xinyu Yao, Lehigh University
时间：7月12日（周四）10:00
单位：清华大学
地点：理科楼B315会议室
Due to the mission configuration, in 74% of the observed area, TESS can only capture one or two transits for planets with orbital periods longer than 13.5 days, which means the true ephemerides will be difficult to determine from TESS data alone. The Kilodegree Extremely Little Transit (KELT) survey has a long observation baseline and monitors fields that largely overlap with the TESS footprint, and also observes stars of similar brightness. We insert simulated TESS-detected single transits into KELT light curves, and find that KELT photometry can be used to confirm ephemerides with high accuracy for planets of Saturn size or larger with orbital periods as long as a year, and therefore span a wide range of planet equilibrium temperatures. In a large fraction of the sky our average recovery rate can be as high as 40%. The resulting periods and ephemerides of the signals can then be used by follow-up teams, to plan and coordinate follow-up observations to confirm candidates as planets, eclipsing binaries, or other false positives, as well as to conduct detailed transit observations with facilities like JWST or HST.
报告人：张坚地
时间：7月12日（周四）14:00
单位：中科院物理所
地点：M236
张坚地教授将与大家分享自己的人生经历，分享自己对科学的兴趣， 人生道路的抉择，科研生涯的历程，希望对同学们有所借鉴。
8. 隐身漫谈
10. 四十载风雨兼程再出发初心不忘——写在中国科学院理论物理研究所建所40 周年之际
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