基於氧化物的電子突觸器件及類腦計算研究||本周物理學術講座

1基於氧化物的電子突觸器件及類腦計算研究

報告人：吳華強，清華大學微納電子系

時間：9月21日（周四）16:00

單位：清華大學物理系

地點：理科樓鄭裕彤講堂

人工智慧的研究和應用已經取得了突飛猛進的發展，但是運行人工智慧深度神經網路演算法的計算平台主要是超級計算機群（成百上千個CPU和GPU）,不但需要巨大的硬體投入，而且佔用的空間和消耗的能源也非常可觀。受限於存儲計算分離對晶元性能的限制，同時CMOS工藝微縮速度放緩，以及人工智慧應用對計算存儲需求的不斷提升，當前的技術將面臨諸多新的挑戰。在這一背景下，新器件的出現變得至關重要，通過引入新原理的半導體器件，不但可以拓展晶元的功能，甚至可以顛覆傳統電路理論，突破當前晶元面臨的能效、速度瓶頸，大幅提升晶元性能。基於過渡族金屬氧化的憶阻器件顯示出了優越的存算一體的特性，能夠規避存儲和計算之間數據搬運的功耗並且能夠實現大規模集成，進而實現高性能計算。展望未來，智能社會即將來臨！面向未來的智能晶元，最底層的器件需要具備哪些特性呢？

2In Situ Synchrotron XRD Studies on the Synthesis of Cathode Materials for Li-Ion Battery

報告人：Jianming Bai， Brookhaven National Laboratory

時間：9月19日（周二）10:30

單位：中科院物理研究所

地點：D樓二層210會議室

In-situ, real-time tracking of the structural chemistry evolution during the synthesis reactions can provide details on reaction process, elucidating intermediate phases and how temperature, pressure, time and the precursor concentrations affect the kinetic reaction pathways. Synchrotron X-ray powder diffraction (SXPD), with its high beam intensity and angular resolution, allows in situ structural characterization in short time scales capable of catching subtle structure changes in the materials under synthesis. The presentation will introduce the in situ SXRD techniques developed at NSLS and NSLS-II, as applied in study of synthesis processes of cathode materials for Li-ion batteries. Specific examples will be given to show how the insights gained from in-situ studies may provide guidance to rational design and synthesis of new battery materials.

3Berry Phase in Strongly Interacting Fermions

報告人：陳靜遠

時間：9月20日（周三）16:00

單位：清華大學物理系

地點：理科樓C302報告廳

Non-Fermi liquid is a class of states of matter emerged from strongly interacting fermions, characterized by the absence of stable quasiparticle excitation, and hence drastically deviate from our Fermi gas intuition. Many studies on such systems are based on phenomenological propositions; concrete theoretical results are extremely rare and any of them can serve as a long-term anchor of the field. I will present that one particular response property -- the static magnetic response -- can be derived from first principles under very general assumptions. The result is formulated in terms of Berry curvature, which is a concept widely used for non-interacting fermions, but here adopted for strongly interacting fermions.

4Ultrafast Spectroscopy Characterization toward Next Generation High Performance Electronic and Optoelectronic Devices

報告人：孫棟，北京大學

時間：9月20日（周三）10:10

單位：北京大學現代光學研究所

地點：物理樓中樓211

Ultrafast science & technology is one of the most exciting fields in science and engineering today. In this talk, first I』ll introduce basic aspects about ultrafast spectroscopy and its role towards the development of next generation high performance electronic and optoelectronic devices. Then I』ll describe several representative work regarding ultrafast spectroscopy characterization of two dimensional materials and topological materials that were performed in ICQM by our group during the past few years. These work includes the following: valley polarization dynamics and exciton dynamics of transitional metal dichalcogenides MoS2; anisotropic response of black phosphorus under high electric field and high magnetic field; and photo response of three dimensional Dirac/Weyl semimetals.

5Open-closed rational conformal field theories

報告人：Liang Kong，Tsinghua University

時間：9月20日（周三）15:30

單位：中科院理論物理研究所

地點：Room 322, ITP

In this talk, I will give a review of the mathematical foundation of the boundary-bulk (or open-closed) rational conformal field theories. In particular, we will discuss all the ingredients of an open-closed conformal field theory, including bulk fields OPE, boundary fields OPE, boundary conditions, modular invariance conditions, Cardy conditions, boundary states, etc. As a consequence, we obtain a precise mathematical description of open-closed rational conformal field theories. Using this precise mathematical language, one can formulate precisely and prove rigorously the so-called "boundary-bulk duality" (or open-closed duality). If time permits, I can also briefly mention how it leads to a complete classification of gapless edges of 2+1D topological orders.

6Star Formation Across Cosmic Time

報告人：Yong Shi，Nanjing University

時間：9月21日（周四）14:00

單位：清華大學物理系

地點：蒙民偉科技南樓 S727

Stars including our Sun are born in clouds of cold gas. Understanding how gas converts into stars across cosmic time is a big challenge in modern astronomy. In the early universe, primordial gas with little or no metals collapse into early-generation stars whose radiation re-ionizes the universe. The subsequent rising of the cosmic star-formation-rate (SFR) density until z～2 follows by a rapid decline toward the current universe. The driving mechanism of this cosmic SFR evolution is related to the cold gas reservoir available within the galaxies and its capability of forming new stars. In this talk, I will review recent progresses including our own works in understanding the evolution of cosmic star formation, with the focus on answering three key questions: how does cosmic star formation start, how does cosmic star formation evolve, and how does star formation stop?

7Probing Light-Matter Interactions in Polar Semiconductor Materials

報告人：Qihua Xiong，Nanyang Technological University

時間：9月21日（周四）14:00

單位：清華大學物理系

地點：理科樓C302報告廳

The interaction of light with matter gives rises to a wide range of linear and nonlinear phenomena that we are familiar with, such as absorption and scattering, spontaneous or stimulated emission, and second harmonic generation. In polar semiconductors, the electromagnetic field of light polarizes the matter leading to the formation of elemental excitations such as excitons and exciton polaritons, due to long-range dipolar force as well as additional coupling to the optical fields.

8Dirac physics and topological photonics

報告人：蔣建華，蘇州大學

時間：9月21日（周四）14:00

單位：北京大學現代光學研究所

地點：物理樓中樓211

The celebrated Dirac equation is not only the foundation of quantum field theory, but also the parent model of many later advances in physics. One of thekey notion derived from Dirac equation is the band topology for fermions in various condensed matters. Recently this notion is extended to bosonic systems, such as in photonics. I will briefly introduce the background, fundamental challenges and recent advances in the search of photonic topological materials. Band degeneracy and topology enriched by space symmetry in all dielectric photonic crystals is emphasized. Synergy with linear and quantum optics is also introduced.

9Optical response of metal nanostructures controlled by mode coupling and interference

報告人：阮智超，浙江大學

時間：9月22日（周五）14:00

單位：北京大學現代光學研究所

地點：物理樓中樓211

In this talk, we briefly review our recent efforts on the manipulation of the light scattering, absorption, and mode excitation through the mode coupling and interference. Especially, we develop a general coupled-mode theory to capture the ubiquitous nature of mode coupling and interference and give a unified picture from both the temporal and the spatial views. Based on the temporal coupled-mode theory, we will show how to design nanowire structures to realize strong absorption enhancement or substantially reduced scattering in the applications of cloak sensors, transparent electrodes and photodetector. As the examples for the spatial domain, we will discuss how to concentrate the surface plasmon polariton (SPP) excitation through the prism coupling method and how to achieve the spatial differentiator and integrator based on a simple Kretschmann prism configuration.

10Cold gas in galaxies: single-dish surveys in the

報告人：Barbara Catinella，University of Western Australia

時間：9月22日（周五）15:00

單位：清華大學物理系

地點：蒙民偉科技南樓 S727

A detailed knowledge of how gas cycles in and around galaxies, and how it depends on their structural and star formation properties, as well as environment, is crucial to understand galaxy formation and evolution. This requires sensitive surveys of cold gas for representative samples of galaxies, able to probe the gas-poor regime. I will present results based on the recently completed, extended GALEX Arecibo SDSS Survey (xGASS), which includes the deepest observations of cold gas in galaxies currently available, and will discuss results obtained via spectral stacking of the largest stellar mass-selected sample with atomic hydrogen data assembled to date. I will argue that, even in the era of the Square Kilometre Array and its precursors, there are important scientific areas where large single-dish telescopes such as Arecibo and FAST can uniquely contribute.

11走向統一的自然力（上）

報告人：厲光烈，中科院高能物理研究所

時間：9月22日（周五）16:00

單位：中科院理論物理研究所

地點：Room 322, ITP

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