逐渐睁开的中国天眼 | 本周物理学讲座

来源：中国物理学会期刊网

1逐渐睁开的中国天眼

报告人：姜鹏，中国科学院国家天文台 研究员、 FAST总工程师

时间：9月6日（周五）14:00

单位：中科院物理研究所

地点：M236会议室

在贵州与世隔绝的群山深处，有一片叫“大窝凼”的天然洼地，2016年9月25日，“500米口径球面射电望远镜”（FAST）在此落成启用。这口深山里的“超级大锅”，是目前世界上最大和最灵敏的单口径射电望远镜。它的建设、调试和运行经历了怎样的故事，凝结了多少中国人的智慧和勤劳，又达成了哪些重要的科学成果？本次讲座将为您详细介绍“中国天眼” 的故事。

2An STM view on correlated electron systems: from heavy fermion metals to topological Kondo insulators

报告人：Steffen Wirth，Max Planck Institute for Chemical Physics of Solids

时间：9月3日（周二）10:00

单位：中科院物理研究所

地点：M楼236会议室

Electronic correlations give rise to a plethora of interesting phenomena and phases. For example, hybridization between 4f and conduction electrons in heavy fermion metals may result in the generation of low-energy scales that can induce quantum criticality and unconventional superconductivity. One of the most important techniques that helped shaping our understanding of nonlocal correlations, both magnetic and superconducting, has been scanning tunneling spectroscopy (STS) with its unique ability to give local, microscopic information that directly relates to the one-particle Green's function. We combine STS with bulk measurements to obtain complementary information on different length scales. We compare hybridization effects as observed by STS, focusing on the model heavy fermion metal YbRh2Si2 and the intermediate-valence Kondo insulator SmB6. Investigation of high-quality single crystals of YbRh2Si2 allows to study the evolution the single-ion Kondo effect and lattice Kondo coherence upon lowering temperature. We also show how Kondo coherence connects with quantum criticality. Low-temperature in-situ cleaving of SmB6 single crystals mostly resulted in reconstructed surfaces, while non-reconstructed patches were found less frequently. The different surface terminations give rise to marked differences in the STS results; in our analysis, however, we concentrate on STS of non-reconstructed areas. These spectra confirm the hybridization picture typically considered for this material. At the surface, the Kondo effect is suppressed to lower temperatures as compared to the bulk material. We show the development of the surface states at low temperatures and how it is locally suppressed around magnetic impurities. The latter is consistent with a topological nature of these surface states.

3A hybrid LBM-DEM numerical approach with an improved immersed moving boundary method for complex particle-liquid flows involving adhesive particles

报告人：Wenwei Liu，University of Surrey

时间：9月3日（周二）10:00

单位：中科院理论物理所

地点：ITP South Building 6420

This work presents a hybrid numerical framework for modelling solid-liquid flow with particle adhesion based on a coupled single-relaxation-time lattice Boltzmann method (LBM) and a discrete element method (DEM) for adhesive particles. The LBM is implemented with an improved immersed moving boundary (IMB) method for solving complex fluid-particle interactions using a fast linear approximation of partially intersected volume between a particle and a lattice cell. It is shown that the linear approximation of the solid fraction is very efficient with good accuracy. In order to model particle adhesion, the Johnson-Kendall-Roberts (JKR) adhesive contact mechanics is adopted with a novel implicit solution to obtain the particle-particle normal force in the DEM. The developed hybrid IMB-LBM-DEM numerical framework is verified with several benchmark tests. The results confirm that the hybrid numerical approach is capable of deriving more detailed flow field between dense particles with relatively low grid resolution, as well as effectively capturing the adhesive mechanics between microspheres.

4Stringy Effects at Low-Energy Limit

报告人：马承德，South China Normal University & University of Cape Town

时间：9月3日（周二）14:30

单位：中科院理论物理所

地点：ITP South Building 6420

In the simple case of bosonic closed string theory with one of the twenty-five spatial directions being a circle of radius $R$, one has to take the field-theory limit $R\gg\sqrt{\alpha^{\prime}}$ to study the low-energy physics. The corresponding massless spectrum, which does not have the winding number and internal momenta excitation, is obtained when the left-moving and right-moving oscillator numbers equal to one, i.e.  $N_L=N_R=1$. This condition characterizes the strong constraint solutions in Double Field Theory. When, in the context of this letter,  one considers instead $N_L\neq N_R$, then the strong constraint solution is not enough to take into account the massless states with nontrivial internal momentum and winding number. This stringy effect in the low-energy limit should be expected from a perturbation in the parameter $\sqrt{\alpha^{\prime}}/R$. We use a linear gauge transformation to construct the quadratic action with a new mass term for the state $(N_L, N_R)=(2, 0), (0, 2)$, and the action is T-dual invariant. By obtaining a gauge transformation for a non-linear extension, a constraint acting on fields can be uniquely defined in triple-products. Finally, we show that the stringy effects only appear in the higher dimensional compact dimensions.

5界面调控光催化性能及其与长余辉材料的复合研究

报告人：王育华，兰州大学

时间：9月3日（周二）15:30

单位：北京航空航天大学

地点：凝聚态物理研究中心113二楼会议室

6Formation of Galaxy Clusters — from the Core to the Outskirts

报告人：Congyao Zhang，MPA, Garching Germany

时间：9月4日（周三）12:00

单位：北京大学

地点：KIAA 1st Meeting Room

Galaxy clusters are the largest virialized structures in our Universe, which contains massive dark matter halos and very hot intracluster medium (ICM). Generally speaking, galaxy clusters evolve in a self-similar way. But there are two main processes that could break the self-similarity of galaxy clusters, i.e. active galactic nucleus (AGN) feedback and cluster mergers. In this talk, I will discuss the effects of these two processes on the formation of galaxy clusters. In the cluster center, X-ray bubbles are inflated by the powerful jets and buoyantly rise outwards. Internal waves excited by these buoyant bubbles may play a very important role in heating the ICM. On the other hand, cluster mergers could re-distribute the matter in galaxy clusters on the Mpc scale. Shock fronts and contact discontinuities are naturally formed during this supersonic process. Our study shows that the merger shock could detach from the gas halo which drives it and travels to the large cluster radius. A "habitable zone" populated by the runaway merger shocks may exist in cluster outskirts, where the shock strength can be maintained or even amplified. 

7基于电子自旋的可靠而环保的物联网终端

报告人：刘小晰

时间：9月4日（周三）14:00

单位：北京航空航天大学

地点：沙河校区国实C座626

8早期宇宙强相互作用物质的演化

报告人：刘玉鑫，北京大学

时间：9月5日（周四）13:30

单位：中国科学院大学

地点：雁栖湖校区 教1-208

9Complementary test of the model by the synergy between measurements of gravitational waves and Higgs couplings

报告人：Katsuya Hashino，Peking University

时间：9月5日（周四）15:00

单位：中科院理论物理所

地点：ITP South Building 6620

The baryon asymmetry of the universe is one of the phenomena beyond the standard model and can be explained by the electroweak baryogenesis. This scenario require the strongly first-order electroweak phase transition in order to realize the asymmetry. The model with extended Higgs sector can easily satisfy the condition. Also, if the phase transition occurs discontinuously, the gravitational wave can be produced by the phase transition and the spectrum of it depend on the form of the potential. Therefore, we may use not only collider experiments but also the gravitational observation experiments to test the new model. In this talk, we discuss wether we can complementarily test the extended Higgs model by the synergy between measurements of gravitational waves and Higgs couplings.

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