米级二维单晶材料的生长及性质调控 | 本周物理学讲座

来源：中国物理学会期刊网

1米级二维单晶材料的生长及性质调控

报告人：刘开辉，北京大学

时间：6月5日（周三）15:00

单位：中科院物理研究所

地点：M楼236会议室

量子材料，包含拓扑材料、超导材料、二维材料等，是非常有望带来颠覆性应用的新型材料。二维材料由于其与当代硅基芯片工艺兼容而有望实现规模化应用，成为当代跨学科交叉研究的热点材料体系。二维材料由于其原子层结构而具有极大的比表面积，其电子态和声子态都分布在表面。因此二维材料对界面非常敏感，跟其它材料在界面上的相互作用可以显著地改变其生长动力学和物理性质。通过设计和利用这种界面相互作用，我们可以调控二维材料的生长和性质。在这个报告中我将介绍近期我们在二维材料界面调控方向开展的一些工作，主要包括：利用表面局域元素供应调控二维材料的生长速率、利用单晶金属衬底周期势调控米级二维单晶石墨烯、六方氮化硼外延生长，利用石墨烯狄拉克能带结构调控二维界面载流子传输动力学。

2Does tunneling process cost time?

报告人：李卫东，山西大学理论物理研究所

单位：中科院物理研究所
时间：6月4日（周二）10:00

地点：M238会议室

A clear consensus on how long it takes a particle to tunnel through a potential barrier has never been so urgently required, due to the attoscecond time resolution in strong-field ionization experiments. A naïve quantum travel time is introduced by the ratio of the travel distance to the expected value of the velocity operator under the barrier. The validity of this definition is checked by considering the analytical solvable mode, rectangular barrier tunneling. In the case of attoclock experiment, the tunneling delay time could be interpreted as a travel time spent by the electron to tunnel from a point under the barrier to the tunnel exit. In addition, a peculiar oscillation structure in the wavelength dependent tunneling delay time in deep tunneling regime is predicted, which is beyond the scope of adiabatic tunneling picture. This oscillation structure can be attributed to the interference between the ground state tunneling channel and the excited states tunneling channels.

3Quantum chaos, Black holes, Periodic Table of SYK and supersymmetric SYK

报告人：叶锦武，首都师范大学

时间：6月4日（周二）10:00

单位：中科院物理研究所

地点：M255会议室

We will first review the recent progress in SYK models and their global impacts in quantum gravity, QCD, condensed matter physics and quantum information science. Then we will outline the results achieved in our recent works in. This colloquium is pedagogical, so should be accessible to any graduate students who are interested in working on this still rapidly expanding research direction and other related directions such as many body localization (MBL), eigenstate thermalization hypothesis (ETH), complexity, etc.

4Emergent phenomena in correlated oxides close to metal-insulator transition

报告人：陈航晖

时间：6月4日（周二）10:00

单位：中科院物理研究所

地点：M830会议室

Correlated oxides exhibit a wide range of exotic phenomena from metal-insulator transition, colossal magnetoresistance to high-temperature superconductivity. In this talk, we focus on one class of correlated oxides that are close to metal-insulator transition. Upon external perturbations, new phenomena  emerge in those correlated oxides. Specifically, we show that: i) a magnetic transition can simultaneously induce an orbital-selective insulator-metal transition in rock-salt ordered oxides A2BB'O6 where B is a non-magnetic ion and B' a magnetic ion with a d3 electronic configuration (Ru5+ and Os5+). The orbital selectivity originates from geometrical frustration of a face-centered-cubic lattice on which the magnetic ions B' reside; ii) in (SrRuO3)_1/(SrTiO3)_N superlattices, the Ru magnetic anisotropy is changed from two-fold along <001> axis (N<3) to eightfold along <111> axis (N>=3). The reorientation of the Ru magnetic easy axis is due to a new orbital ordering which significantly tunes the underlying spin-orbit interaction. 

5Variable stars in the era of large-scale surveys (special seminar)

报告人：Nami Mowlavi，University of Geneva

时间：6月4日（周二）10:30

单位：清华大学

地点：蒙民伟科技南楼S727

Variable stars play an increasingly preponderant role in modern astronomy. They are key, for example, in the determination of cosmological distances, in probing the internal structures of stars, in the study of Galactic structure, and in the discovery of exo-planets. The advent of large-scale multi-epoch surveys since a few decades is further boosting the field. Among these surveys, ESA's Gaia mission is unique by the provision of astrometric, photometric and spectro-photometric data in a homogeneous way for more than 1.5 billion stars across the entire sky, together with spectroscopic data for the bright stars.

In this seminar, I will illustrate these considerations with the case of long-period variables. I will review their properties and their relevance for the study of the Galaxy and extra-galactic systems, and present the first catalog of these objects released by the Gaia mission in its second data release one year ago.

6The evolving soliton microcombs

报告人：Qifan Yang

时间：6月4日（周二）13:30

单位：清华大学

地点：物理系理科楼C302

Optical frequency combs are having a broad impact on science and technology by pushing metrology of time and frequency to the best accuracy. Integration of these systems on photonic chips would revolutionize the instrumentation as well as a wide range of subjects. Such miniaturized approach has been proposed in high-quality-factor (high-Q) microresonators and was recently leveraged by the demonstration of mode locking through the formation of light bullets called optical solitons. In this talk I will trace the development of soliton microcombs including their physical origins. I will also cover discoveries of novel nonlinear phenomena in soliton microcombs, followed by ground-breaking applications spanning spectroscopy and telecommunication to chip-based optical frequency synthesizers and atomic clocks.

7Machine learning meets quantum physics

报告人：Dong-Ling Deng，Tsinghua IIIS

时间：6月5日（周三）10:00

单位：中科院物理研究所

地点：M830

Recently, machine learning has attracted tremendous interest across different communities. In this talk, I will briefly introduce some new progresses in the emergent field of quantum machine learning ---an interdisciplinary field that explores the interactions between quantum physics and machine learning. On the one hand, I will talk about several quantum algorithms that promise an exponential speed-up for machine learning tasks. On the other hand, I will show how ideas and techniques from machine learning can help solve challenging problems in the quantum domain. In particular, I will talk about how to use machine learning to identify nonergodic metals in a many-body localized system and 3D chiral topological insulators with experimental data observed from a solid-state quantum simulator.

8Electric field control of spin-charge interconversion in ferromagnetic-free oxide Rashba nanodevices

报告人：Felix Trier，University Paris-Saclay

时间：6月5日（周三）14:30

单位：中科院物理研究所

地点：M楼253会议室

A plethora of exciting properties have been observed at the oxide heterointerface between LaAlO3 and SrTiO3. Most prominently it has been demonstrated that the confined electron gas formed at the interface features e.g. gate-tunable superconductivity, ferromagnetism and a sizeable Rashba spin-orbit coupling. This Rashba spin-orbit coupling allows a considerable charge/spin interconversion to take place at this particular interface as previously demonstrated by spin pumping ferromagnetic resonance experiments from a NiFe contact. Moreover, the efficiency of this charge-to-spin conversion was demonstrated to be strongly tunable by a gate voltage. Transport experiments of patterned LaAlO3/SrTiO3 devices have also allowed detection and quantification of this charge-to-spin conversion through non-local resistance measurements. Here, we probe spin/charge interconversion through the two-dimensional spin Hall effect in patterned amorphous-LaAlO3/SrTiO3 planar nanodevices using the Hanle effect. Specifically, we investigate the dependence of the non-local spin resistance as a function of back-gate voltage, temperature, channel length and magnetic field angle. From these measurements, we observe a large non-monotonic modulation of the spin Hall angle and characteristic spin diffusion length when the back-gate voltage is varied. Most notably, we observe a spin diffusion length of up to ~1 μm at 2 K for certain gate voltages, which compared with the spin diffusion length in e.g. Pt of ~4-5 nm at 2 K, highlights this particular oxide interface as a strong candidate for spintronic applications.

9Effective field theory approach to lepton number violation: dimension seven operators

报告人：廖益，南开大学

时间：6月5日（周三）15:00

单位：中科院理论物理所

地点：ITP South (New) Building 6420

Effective field theory offers an appropriate approach to lepton-number violating processes at low energy and to connecting to origin of lepton number violation at high energy scale. In this talk I'll focus on dimension seven operators appearing in standard model effective field theory. I'll discuss their completeness and independence, and their renormalization. I'll explain how to extract anomalous dimensions for a suitably chosen basis of operators constrained by nontrivial flavor relations. As simple illustrations, I'll estimate renormalization effects on neutrinoless double beta decay and unusual proton decay.

10Recent advances on first-principles study of Dzyaloshinskii-Moriya interaction at interfaces

报告人：杨洪新，中科院宁波材料技术与工程研究所

时间：6月5日（周三）15:00

单位：北京师范大学

地点：物理楼105

The antisymmetric exchange interaction, Dzyaloshnskii-Moriya Interaction (DMI), has become recently a subject of tremendous interest for both fundamental research and applications due to its crucial role in the creation, annihilation and the influence on the dynamics of magnetic Skyrmions and chiral domain walls. Here, I will present a general DMI calculation approach based on DFT total energy calculations. I will address the main features and microscopic mechanism of typical Fert-Levy type DMI at interfaces between ferromagnetic and heavy metals by clearing up several fundamental questions: how does the DMI extend away from the interface? Where is the corresponding electronic energy source located? How to design structures with enhanced DMI? Moreover, I will show results at ferromagnet/graphene interfaces beyond Fert-Levy type DMI. At the end, I will present some new results of DMI and Skyrmion study based on 2D ferromagnets. 

11C and CP Violation in η → π+ π- π0

报告人：史君，University of Kentucky

时间：6月6日（周四）10:00

单位：中科院理论物理所

地点：ITP North Building  322

The CP violating effects observed thus far appear only in flavor-changing processes and in a manner consistent with the predictions of the Standard Model (SM). The observed baryon asymmetry of the universe suggests that new mechanisms of CP violation beyond the SM should appear. Most searches for new sources of CP violation focus on processes that break P and CP, whereas processes that would break C and CP are not well studied. The decay η →π+ π- π0is an ideal process in which to search for C and CP violation. In this talk, I will analyze the C and CP violating patterns in the Dalitz plot distribution of η → π+ π- π0decay and discuss the implications of existing experiments.

12Computational methods for the dynamics of the nonlinear Schroedinger/Gross-Pitaevskii equations

报告人：Weizhu Bao，National University of Singapore

时间：6月6日（周四）15:00

单位：中科院理论物理所

地点：Room6620,ITP South Building

In this talk, I begin wtih the nonlinear Schroedinger/Gross-Pitaevskii equations (NLSE/GPE) for modeling Bose-Einstein condensation (BEC), nonlinear optics, quantum physics and chemistry, etc., and review some dynamical properties of NLSE/GPE including conserved quantities, dispersion relation, center-of-mass dynamics, soliton solutions and semiclassical limits. Different numerical methods will be presented including finite different time domain (FDTD) methods and time-splitting spectral method, and their error estimates and comparison will be discussed. Extensions to NLSE/GPE with an angular momentum rotation term and/or non-local dipole-dipole interaction as well as multi-component will be presented. Finally, applications to soliton interactions, collapse and explosion of BEC, quantum transport and quantized vortex interaction will be investigated.

13一维量子气体可积非平衡过程的物理实验研究

报告人：陈徐宗，北京大学

时间：6月6日（周四）16:00

单位：清华大学

地点：理科楼郑裕彤讲堂

一维量子气体的可积问题一直是科学家们感兴趣的问题，也是量子模拟的一个热点问题之一。文本通一维超冷玻色原子量子牛顿摆实验，研究原子在一维系统中的退相位和弛豫。原则上，一个在非平衡状态下的可积系统不会随着时间而达到平衡态，但是实际系统中总会达到平衡，如何从可积系统达到平衡，这是一直是个未解之谜。我们的实验表明：（1）每个原子的初始能量低于一维系统的横向激发能，经历了几百个振荡周期，接近可积模型。（2）由于存在横向激发态原子，从而破坏了系统的可积性，增加了系统的弛豫速率。这些实验结果证明了一维玻色气体的可积性，并解释了系统最终达到平衡的原因。

14General Overview of Physics and Applications OF WGM

报告人：Lan Yang，Washington University

时间：6月7日（周五）09:00

单位：中科院半导体研究所

地点：图书馆101会议室

15Topological Monopoles in Transition Metal Dichalcogenides

报告人：颜丙海，Weizmann Institute of Science, Israel

时间：6月7日（周五）10:00

单位：北京师范大学

地点：物理楼105

The past decade has witnessed intensive research investigating the role of band-structure topology and discovering topological materials. In this talk, I will introduce our most recent progress on the Weyl semimetal phase discovered in a well-known family of compounds, transition metal dichalcogenides (WTe2 and MoTe2). The band crossing point exhibits “monopole” structure of the Berry curvature, giving rise to Weyl fermions with unique properties such as the chiral anomaly and Fermi arcs. Further, a nonlinear anomalous Hall effect, distinct from the ordinary Hall effect, was predicted to exist due to the topological monopoles. This exotic phenomenon was observed in experiment recently.

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