理论热学：变换热学及其衍生理论与热超构材料(2008-2019) | 本周物理学讲座

　　1理论热学：变换热学及其衍生理论与热超构材料(2008-2019)

　　报告人：黄吉平,复旦大学

　　时间：3月27日（周三）16:00

　　单位：中科院理论物理所

　　地点：新楼6620报告厅

　　变换热学理论是指基于两种不同空间之间的坐标变换而实现的一种把空间几何参数精确耦合进热导率等热学物理量的一种理论方法。自由操控热流一直是人类的一个梦想，热超构材料正是为此目的而生，它起源于变换热血理论。在此，我将汇报该领域自2008年变换热学理论诞生以来取得的若干理论和实验研究进展，它主要包括以下新奇热现象或功能器件：热隐身；热聚集；热旋转；宏观热二极管；热伪装；热透明；热模仿；热学“点石成金”；热晶体；环境温差中零能耗和负能耗保温；热对流隐身、聚集、伪装；热辐射制冷；等等。我将汇报与之相关的微观或宏观传热机制，亦将对该领域未来发展做若干展望。其后，将以热隐身和零能耗保温为例，重点介绍其中的具体理论。本报告内容涉及热防护、热探测、热控制或热管理。

　　2Sub-mHz Spectral Purity Transfer for Next Generation Strontium Optical Atomic Clocks

　　报告人：Ronald Holzwarth，CTO of Menlo Systems

　　时间：3月26日（周二）14:00

　　单位：清华大学

　　地点：物理系理科楼C302

　　As the optical frequency standards based on cold atoms and ultra-stable cavity-stabilized laser continue to be improved, the demand of optical frequency combs that are used as clockwork is increasing as well. Recently, Matei et al. demonstrated a laser source with a record-breaking sub-Hz linewidth with very low frequency drift. Optical lattice clocks with Strontium atoms interrogated in a cryogenic environment have been demonstrated at 10-18 level of accuracy and stability. Moreover, the first Fermi-degenerate three-dimensional optical lattice frequency standard has also been reported, showing the potential to overridden the tradeoff between low quantum projection noise limit and density-dependent frequency shifts. Due to technical reasons the central frequency of the ultra-stable lasers is at approximately 194 THz, while the clock transition of neural Strontium atoms is centered around 429 THz. Here, we demonstrate a clockwork for spectral purity transfer from a 1542 nm reference laser to the interrogation wavelength of a Strontium clock at 698.44nm, paving the way for a novel level of instability and inaccuracy at 10-19 at 100 second for optical frequency measurement.

　　3More on gravitational memory

　　报告人：毛普健，天津大学

　　时间：3月26日（周二）15:30

　　地点：Room 6420, ITP NEW BUILDING

　　In this talk, I will first review the gravitational memory in Newman-Penrose formalism. Then I will show in details the memory formula in the case of an arbitrary conformal factor on the boundary and the geometric interpretation of the spin memory discovered very recently by Pasterski, Strominger, and Zhiboedov.

　　4Disentangling galaxy formation history through a population-orbit superposition model

　　报告人：Ling Zhu

　　时间：3月27日（周三）12:00

　　单位：北京大学

　　地点：KIAA 1st meeting room

　　Stellar kinematics is a fossil record of galaxy formation and evolution.In particular, the fraction of stars on approximately circular and co-planar orbits, compared to the fraction of stars on kinematically hotter and geometrically rounder orbits, speaks directly to the slowly accretion of gas flow or violent merging/feedback of the galaxies’ past. On the other hand, stars conserve chemical properties since their birth, chemistry is a widely-used indication of stellar age. The combination of stellar kinematics and stellar chemical age may provide us unprecedented information to understand the formation of galactic structures. The IFU surveys, like CALIFA and MaNGA, provide us information integrated along the line-of-sight, including the surface brightness, kinematic maps, mean age and metallicity maps from stellar-population synthesis of the spectra across the 2D sky-plane.Using the orbit-superpostion Schwarzschild method, we have been able to derive the internal stellar orbit distribution for a sample of 300 CALIFA galaxies, which form an orbit-based ‘dynamical Hubble sequence’.Decomposition of different orbital structures is thus possible based on the orbit distribution. In order to obtain chemical information of these orbital structures, we further develop a population-orbit superposition model, by tagging age and metallicities to the orbits in the Schwarzschild model. This is an on-going work, I will show you various method-tests and some preliminary results of application to MUSE observed galaxies.

　　5Soft supersymmetry breaking of four dimensional superconformal field theory

　　报告人：Dan Xie，Tsinghua University

　　时间：3月27日（周三）14:30

　　地点：新楼6420报告厅

　　I will discuss classification of soft supersymmetry breaking of four dimensional superconformal field theory (SCFT). Some deformations of N=2 SCFT would give us new N=1 SCFT and more interestingly new non-supersymmetric conformal field theory.

　　6Nonlinear Hall effect

　　报告人：Hai-Zhou Lu

　　地点：Room W563, Physics Building

　　Unconventional responses upon breaking discrete or crystal symmetries open avenues for exploring emergent physical systems and materials. By breaking inversion symmetry, a nonlinear Hall signal can be observed, even in the presence of time-reversal symmetry, quite different from the conventional Halleffects. However, less is known when a strong nonlinear Hall signal can be measured, in particular, its connections with the band-structure properties. By using model analysis, we find prominent nonlinear Hall signals near tilted band anticrossings and band inversions. These band signatures can be used to explain the strong nonlinear Hall effect in the recent experiments on two-dimensional WTe2. Disorder plays indispensable roles in various linear Hall effects. We derive the formulas of the nonlinear Hall conductivity in the presence of disorder scattering and construct the general scaling law of the nonlinear Hall effect, which may help in experiments to distinguish disorder-induced contributions to the nonlinear Hall effect.

　　7Observation of Higgs Boson Decays to a pair of Bottom Quarks with the ATLAS Detector

　　报告人：李昌樵，中国科技大学

　　时间：3月28日（周四）10:00

　　单位：中科院高能物理所

　　地点：B326, main building

　　In the standard model prediction, Higgs Boson is expected to decay to a pair of b-quarks, with a branching ratio of about 58%. Thus probing this decay is indispensable for the understanding of the property of the Higgs boson. In this seminar, a search for the Higgs to bb decay is presented using 79.8 fb-1 of 13 TeV LHC Run2 data.

　　8Full symmetry classification of avoided Landau-level crossings

　　报告人：Aris Alexandradinata

　　单位：中科院物理研究所

　　地点：M830

　　Landau levels generically repel due to a combination of the spin-orbit coupling and the Zeeman interaction. In this talk, we ask how many real parameters are needed to tune to a spin degeneracy in the Landau-level spectrum. In the absence of crystallographic point-group symmetries, three real parameters are needed. We have exhaustively identified all symmetry classes of cyclotron orbits for which this number is reduced from three, thus establishing symmetry-enforced 'non-crossing rules' for Landau levels. In particular, only one parameter is needed in the presence of spatial rotation or inversion; this single parameter may be the magnitude or orientation of the field. Signatures of single-parameter tunability include (i) a smooth crossover between period-doubled and -undoubled quantum oscillations in the low-temperature Shubnikov-de Haas effect, as well as (ii) 'magic-angle' magnetoresistance oscillations. Our theory is applied to the Rashba-Dresselhaus two-dimensional electron gas ( subject to an arbitrarily oriented magnetic field), as well as to a comparative case study between Bismuth (a conventional metal) and Na3Bi (topological).

　　9Formation of binary stellar-mass black holes from globular clusters: the impact of host clusters' properties

　　报告人：Jongsuk Hong

　　时间：3月28日（周四）12:00

　　Globular clusters (GCs) provide a good environment for the formation of black hole binaries (BBHs), some of which can merge with gravitational waves (GW) within the age of the Universe. We have performed a survey of Monte-Carlo simulations to explore the impact of host GC properties on the formation and detection of BBH mergers originating from GCs. We find that the number of BBH mergers from GCs is influenced by not only the initial mass but also the initial half-mass radius and primordial binary fraction of GCs. BBH mergers can be identified by their origins, primordial and dynamical BBH mergers, significantly affecting their properties such as the mass and merging time distributions. In this talk I will provide some empirical relations like the expected number of BBH mergers from individual GCs and the time evolution of merger rates of these BBHs, which can be used to estimate the detection rates.

　　10Gravitational wave astronomy and cosmology- the dawn has arrived

　　报告人：Misao Sasaki

　　时间：3月28日（周四）15:00

　　地点：Room 6620, ITP NEW BUILDING

　　11Energy Harvesting by Spin Current

　　报告人：SADAMICHI MAEKAWA

　　时间：3月28日（周四）16:00

　　The flow of electron spins, the so-called ?spin current?, is a key concept in the recent progress in spintronics. In a ferromagnet, the spin current interacts with magnetization by the exchange interaction and induces the motion of the magnetization due to the angular momentum conservation, the so-called spin transfer torque. Its inverse effect is called the spin-motive force which is the electric voltage generated by the magnetization dynamics due to the energy conservation between electrical current and magnetization. The spin motive-force is derived by extending the Faraday?s law of electro-magnetism.

　　Spin current is induced and manipulated by heat and mechanical motion as well. The interconversion between various energies through spin current , the so-called ?power spintronics?,is discussed.

　　12Cosmological implications of the BOSS and eBOSS galaxy surveys

　　报告人：Gongbo Zhao，NAOC

　　单位：清华大学

　　地点：理科楼郑裕彤讲堂

　　Galaxy surveys can provide key information for cosmological studies through probes of baryonic acoustic oscillations (BAO) and redshift space distortions (RSD). In this talk, I will focus on dark energy and gravity tests on cosmological scales using BAO and RSD measurements derived from the BOSS DR12 and eBOSS DR14 quasar survey. I’ll also discuss how to maximise the information context that can be extracted from large galaxy surveys.

　　13Testing general relativity using X-ray reflection spectroscopy

　　报告人：Cosimo Bambi，Fudan University

　　时间：3月29日（周五）15:30

　　地点：KIAA-PKU Auditorium

　　Einstein's theory of general relativity was proposed over 100 years ago and has successfully passed a large number of observational tests in weak gravitational fields. However, the strong field regime is still largely unexplored, and there are many modified and alternative theories that have the same predictions as Einstein's gravity for weak fields and present deviations only when gravity becomes strong. X-ray reflection spectroscopy is potentially a powerful tool for testing the strong gravity region around astrophysical black holes with electromagnetic radiation. In this talk, I will present the reflection model RELXILL_NK designed for testing the metric around black holes and the current constraints on possible new physics from the analysis of a few sources.