铁电畴和畴壁结构的衍生现象：从类神经突触到低损耗可调微波通讯器件

来源：中国物理学会期刊网

1铁电畴和畴壁结构的衍生现象：从类神经突触到低损耗可调微波通讯器件

报告人：刘仕，西湖大学

时间：7月10日（周三）14:00

单位：北京师范大学

地点：科技楼A区311

Ferroelectrics, a major class of high-coupling materials characterized by the switchable polarization, have become important in modern devices ranging from medical ultrasound, non-volatile memory to vibration-powered electronics. The device functionalities heavily rely on the interactions between the electric polarization and applied stimuli (e.g., electric fields). Understanding the dynamics of ferroelectric domains and domain walls in response to external perturbations is important for the development of ferroelectric-based functional devices. In this talk, I will first introduce a classical force field we developed based on the bond valence theory which enabled large-scale molecular dynamics simulations of typical ferroelectric materials at the million-atom scale. I will then explain a theory-experiment collaboration wherein we demonstrated deterministic and repeatedly obtainable multistate polarizations in ferroelectric thin films, highlighting the potential of ferroelectrics for adaptive neuromorphic electronics. Finally, I will explain how the resonance of domain walls can be exploited to obtain tunable dielectrics with ultralow loss and high tunability.

2VVV MICROLENSING EVENTS, CURRENT STATUS AND FUTURE WORK

报告人：Gabriela Navarro

时间：7月9日（周二）12:00

单位：北京大学

地点：KIAA 1st meeting room

A microlensing event occurs when an object passes near the line sight of a star from earth to a background star generating an apparent increase in brightness. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. We searched for microlensing events in the innermost area of the Galactic bulge using the VVV Survey near-IR data. We discovered a total sample of N=906 events within an area covering ~30 deg^2 between the years 2010 and 2015 (Navarro et al. 2017 and Navarro et al. 2019). We used the near-IR Color-Magnitude and Color-Color Diagram to select events with red-clump sources to analyze the extinction properties of the sample in the central region of the Galactic plane and minor axis (Navarro et al. 2018). The timescale distribution and its dependence in the longitude and latitude axis are presented along with the efficiency analysis to correct those distributions. The minor axis shows a steeper distribution as we approach to the galactic center. This is the first time we can measure the rate of microlensing events down to the innermost areas of the Milky Way. We also detected light curves that do not follow the simple microlensing model and show a binary systems or parallax effect.

3Nuclear Incompressibility: Does It Depend on Nuclear Structure?

报告人：Umesh Garg，University of Notre Dame

时间：7月9日（周二）16:00

单位：中科院理论物理所

地点：ITP South Building 6420

The nuclear incompressibility parameter is one of three important components characterizing the nuclear equation of state. It has crucial bearing on diverse nuclear and astrophysical phenomena, including radii of neutron stars, strength of supernova collapse, and collective flow in medium- and high-energy nuclear collisions. The only direct experimental measurement of this quantity comes from the compression-mode giant resonances—the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant dipole resonance (ISGDR). There have been some experimental results recently suggesting that nuclear structure effects may influence the energy of the isoscalar giant monopole resonance and, hence, the nuclear incompressibility. However, this being a bulk property of nuclear matter, one expects structure effects to play no role in it. In this talk, I will critically examine how, and if, nuclear structure effects play a role。

4What is inside a Black Hole? And some potential applications

报告人：Andre LeClair，The Cornell University

时间：7月10日（周三）10:00

单位：中科院物理研究所

地点：M253会议室

5Predictions of nuclear masses and half-lives with Bayesian neural network approach

报告人：牛中明，Anhui University

时间：7月10日（周三）15:00

单位：中科院理论物理所

地点：ITP South Building 6420

Bayesian neural network (BNN) approach is employed to improve the predictions of nuclear masses and half-lives. It is found that the noise error in the likelihood function plays an important role in the predictive performance for the BNN approach. By including a distribution for the noise error, theoretical predictions can be improved remarkably. In addition to the proton and mass numbers, we further include two quantities related to nuclear pairing and shell effects into the input layer for nuclear mass predictions, and two quantities related to nuclear pairing and reaction energies into the input layer for nuclear half-life predictions. As a result, the theoretical accuracies are significantly improved for both nuclear masses and nuclear half-lives. This manifests that better predictive performance can be achieved if more physical features are included into the BNN approach.

6Antimonide-based devices: the infra-red optoelectronics toolbox

报告人：Eric Tournié，Université de Montpellier

时间：7月11日（周四）10:00

单位：中科院半导体研究所

地点：图书馆101会议室

7Accretion towards SgrA* SMBH in the Milky Way

报告人：Paul Ho，East Asian Observatory

时间：7月12日（周五）12:00

单位：北京大学

地点：KIAA 1st meeting room

SgrA* is the nearest supermassive black hole, located in the nucleus of our Galaxy. There is a large reservoir of gas in the form of a circumnuclear ring at a radial distance of about 1pc. We examine the evidence for accretion towards the nucleus. We argue that magnetic fields play a role in forming the visible structures.

8Auxiliary field quantum Monte Carlo for transition metal systems: from molecules to solids

报告人：石浩，CCQ, Flatiron institute, Simons Foundation

时间：7月12日（周五）15:00

单位：北京师范大学

地点：物理楼106

A major challenge in condensed matter physics, chemistry, and materials is to be able to compute the properties of electrons in real materials. Auxiliary field quantum Monte Carlo is a promising numerical method for these systems. It is proven to be highly accurate and be able to treat large number of electrons in the Simons many-electron collaboration. We apply the state of art auxiliary field quantum Monte Carlo for realistic transition metal systems. The many-body ab initio Hamiltonian is treated directly on transition metal atoms, their ions, and their monoxide molecules. We show ionization energy and dissociation energy on transition metal systems are indistinguishable from experimental results. Then, we studied the low temperature phase diagram of Ca2RuO4 for a range of layered perovskite structures. Our calculations find that the metal-insulator transition in Ca2RuO4 is driven by a structural transition from a long c-axis to a short c-axis perovskite in this material and is accompanied by a ferromagnetic-antiferromagnetic transition. Our many-body simulations capture the phase diagram and explain the origin of the magnetic and metal-insulator transitions in Ca2RuO4.

9The Breakout of Astrophysical Shocks

报告人：Re'em Sari，The Hebrew University

时间：7月12日（周五）16:00

单位：北京大学

地点：KIAA 1st Meeting Room

Shockwaves are abundant in astrophysics, from gamma ray bursts, to supernovae to planetary collisions.In many cases such shocks emerge from the edge of the system, be it the surface of the planet or the edge of the star.We discuss the physics of such shocks. Interesting hydrodynamics solutions allowing acceleration of shocks as they propagate towards the edge, as well as deviation from equilibrium as the dynamical and diffusion timescales become short and photons leak out of the systems. These processes determine the first signals we see from a supernovae or from the electromagnetic counterpart of gravitational wave sources such as neutron star mergers.This dynamics will also set the amount of atmosphere ejected from planets in the process of their formation.

10Origin of the Jamming Scaling Exponents

报告人：Corey S. O'Hern，Yale University

时间：7月14日（周日）11:30

单位：中科院理论物理所

地点：ITP South Building 6420

11Recent Advances on the Glass Problem and its Relationship to Amorphous Packing

报告人：Patrick Charbonneau，Duke University

时间：7月14日（周六）14:00

单位：中科院理论物理所

地点：ITP South Building 6420

Recent theoretical advances in the mean-field theory of glasses predict the existence, deep in the glass phase, of a novel phase transition, a so-called Gardner transition. This transition signals the emergence of a complex free energy landscape composed of a marginally stable hierarchy of sub-basins. It is also thought to be the onset of the anomalous thermal and transport properties of amorphous systems, and to ultimately lead to the unusual critical behavior at jamming. In this talk, I will present an overview of recent theoretical and numerical advances in the field of glasses, paying particular attention to capturing and characterizing the physics of the Gardner phase.

更多报告信息：中国物理学会期刊网学术讲座列表

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