铁基超导、电极材料、配对密度波、量子多体系统 | 本周物理讲座

1 铁基超导体的中子自旋共振模

报告人：洪文山，北京大学

时间：3月14日（周二）14:00

单位：中科院物理所

腾讯会议：819 875 550

会议密码：9849

摘要：

在非常规超导体中，磁性扮演着非常重要的角色。理论上认为，相对于常规超导体中电声子耦合的配对机制，自旋涨落在非常规超导体中可能扮演着类似于电声子耦合中声子的媒介作用。自旋涨落是超导库珀对配对不可忽视的驱动力，这一观点的关键实验证据之一就是中子自旋共振模。由于铁基超导体的多带特性，相比于单带体系的铜氧化物超导体而言，它的中子自旋共振模存在着一些特点：（1）共振能量分布较宽，且面内面外都存在色散；（2）面内面外的色散行为在不同的体系中又有不同的表现；（3）自旋共振模与超导能隙之间的关系没有较好的描述形式等。为了深入了解上述行为的起源，我们挑选并研究了几个体系的铁基超导样品，得出了以下结论：共振能量分布较宽且存在面外色散与超导层之间残存的磁相互作用有关；自旋共振模的面内色散行为与费米面的拓扑形貌有关；超导能隙的色散行为与层间磁相互作用有关。这些研究结果直接揭示了铁基超导体中磁性与电荷/轨道之间的相互作用，对理解非常规超导体中中子自旋共振模的起源以及铁基超导体中的库珀对配对机制有着重大的帮助。

报告人简介：

洪文山博士分别于2016年获得四川大学学士学位 ，2021年获得中国科学院大学博士学位。2021-至今在北京大学物理学院量子材料科学中心开展博士后研究，合作导师为李源研究员。近5年来在Physical Review Letters, Nano Letters,Physical Review B 等国际知名期刊发表相关论文十余篇，其中一作（及共同一作）PRL 3篇，PRB 2篇。2021年至今，获得博新计划支持，并主持中国博士后面上项目。

2 Gravitational waves and fundamental physics with Pulsar Timing Arrays

报告人：陈偲源，北京大学科维理天文与天体物理研究所

时间：3月14日（周二）14:30

单位：中科院理论物理所

地点：理论所南楼6620会议室

腾讯会议：100-934-042

摘要：

Pulsar Timing Arrays (PTAs) search for nHz gravitational waves by timing the radio signals from a network of stable millisecond pulsars and looking for a spatially correlated common signal in the data set. We expect to find a gravitational wave background (GWB) first, followed by possible individual sources. PTAs have reported the finding of a spectrally similar but spatially uncorrelated signal in various data sets, namely North American Nanohertz Observatory for Gravitational waves (NANOGrav), Australian Parkes PTA, European PTA, together with the Indian PTA they form the International PTA. We hope to deepen collaboration with Chinese and South African PTA colleagues.

I will present results from the different PTAs on the search for a GWB. All PTAs report consistent results of a common signal with a nominal amplitude of 2-3e-15, but no characteristic spatial correlation required for a GWB. This putative signal has been tested against both cosmological and astrophysical sources for a GWB and helped to put constraints for various theories. We are working in the four PTA collaborations to collect and analyze the most recent data sets in a coordinated process, including the supervision of an external Detection Committee under the guidance of the IPTA. We hope to have exciting results to present by the end of this year. These new data sets will form the basis for the next IPTA DR3 combination in the coming year.

报告人简介：

Siyuan Chen received his PhD in Physics and Astronomy from the University of Birmingham in the UK under the supervision of Prof. Alberto Sesana in 2018. From 2018 to 2021, he has worked as a postdoctoral researcher at the Centre national de la recherche scientifique (CNRS) in Orleans, France, in the Laboratory for space and evironmental physics and chemistry (LPC2E). During his studies and reasearch Siyuan Chen has been strongly involved with the European Pulsar Timing Array (EPTA). Other collaborations include the Large European Array for Pulsars (LEAP), North American Nanohertz Observatory for Gravitational waves (NANOGrav) and International Pulsar Timing Array (IPTA). At the end of 2021, he has joined the Kavli Institute for Astronomy and Astrophysics at Peking University as a postdoctoral fellow.

3 When nature entangles millions of particles: from quantum materials to black holes & Introduction to quantum spin liquids

报告人：Subir Sachdev，Harvard University

时间：3月14日（周二）16:30

单位：香港大学

会议链接：https://www.koushare.com/lives/roo‍m/412849

摘要：

When nature entangles millions of particles: from quantum materials to black holes

Entanglement is the strangest feature of quantum theory, often dubbed ''spooky action at a distance’’. Quantum entanglement can occur on a macroscopic scale with trillions of electrons, leading to "strange metals" and novel superconductors which can conduct electricity without resistance even at relatively high temperatures. Remarkably, related entanglement structures arise across the horizon of a black hole, and give rise to Hawking’s quantum paradox. This lecture will be designed to introduce these forefront topics in current physics research to a general audience.

Introduction to quantum spin liquids

Spin liquids are novel states of quantum matter featuring excitations with fractionalized quantum numbers, emergent gauge fields, and long-range quantum entanglement. I will use the parton method to describe the simplest spin liquids on the square lattice: those with emergent Z2, U(1), and SU(2) gauge fields. I will also discuss confinement transitions of these spin liquids.

4 基于超导量子电路的量子网络和量子模拟

报告人：钟有鹏，南方科技大学

时间：3月15日（周三）10:00

单位：中科院物理所

地点：M楼253会议室

摘要：

超导量子计算最近几年发展迅速，有望在未来几年扩展到数千个量子比特以上。然而超导量子比特尺寸较大，且每个比特需要专用射频控制线路，随着比特数量的增加，在单芯片上集成更多比特变得越来越困难。分布式量子计算通过把多个量子芯片互联的方式构建大规模量子处理器，该方案可以突破单芯片集成的困境，但是目前芯片间的高性能互联面临技术瓶颈。近期我们在该方向获得一些实验进展，我们通过一根铌钛超导同轴线把两个超导量子芯片连接起来，实现了低损耗的量子芯片互联和高保真度的芯片间量子态传输。在此基础上，我们在一个芯片上制备了3比特GHZ纠缠态，并通过串行的方式确定性地传输到另一个芯片。随后，我们采用一系列技术创新，研发了超低损耗且易于键合连接的超导同轴线，并在量子芯片上集成了阻抗转换器以降低量子芯片连接界面的损耗。通过这些技术创新，我们实现了超高性能的超导量子芯片互联，信道单光子品质因子达到8.1×10^5，较先前的结果提高了一个数量级，信道相干时间（~26.4μs）达到单芯片上量子比特的水平，跨芯片量子态传输的保真度达到99%。在此基础上，我们实现了5个量子芯片的互联，并展示了跨3个芯片的12比特最大纠缠态（GHZ态）。进一步地，我们实现了64米超低损耗同轴线连接的两个量子芯片间的量子隐形传态，为大规模、可扩展分布式量子计算网络奠定了基础。最后，我们在数十比特规模的超导量子处理器上探索了拓扑量子物态等量子模拟应用。

报告人简介：

钟有鹏，南方科技大学量子科学与工程研究院副研究员，博士生导师，入选国家海外高层次青年人才计划、深圳市国家级领军人才、深圳市孔雀团队等项目资助。2013年本科毕业于浙江大学，2015年赴芝加哥大学攻读博士学位，师从Andrew Cleland教授，2019年博士毕业后留在Cleland组继续一年多的博士后研究，于2020年回国加入南方科技大学。长期从事超导量子计算实验研究，发表SCI 论文20 余篇，包括以第一/通信作者在Nature, Nature Electronics, Nature Physics, Nature Communications, PRL等国际期刊发表论文，代表性成果包括多比特最大纠缠态（GHZ态）的跨芯片传输，超低损耗量子芯片互联等。

5 嵌套费米面体系中的配对密度波超导

报告人：金锦涛，中国科学院大学卡弗里理论科学研究所

时间：3月15日 (周三) 14:30

单位：中国科学院大学、香港大学

会议链接：https://www.koushare.com/lives/room/51‍4021

摘要：

1.配对密度波超导简介

2.嵌套费米面与笼目材料AV3Sb5中的配对密度波

3.相关唯象模型计算及结果

报告人简介：

金锦涛，2019年本科毕业于浙江大学。2019年至今，中国科学院大学卡弗里理论科学研究所博士在读。研究兴趣主要集中在非常规超导以及量子自旋液体的理论研究。

6 Probing magnetism in zigzag graphene nanoribbon embedded in h-BN in the ballistic transport regime

报告人：王浩敏，中国科学院上海微系统与信息技术研究所

时间：3月15日 (周三) 15:00

单位：北京大学物理学院

地点：北京大学物理楼，西563会议室

摘要：

Zigzag edges of graphene have long been predicted to exhibit magnetic electronic state near the Fermi level, which can cause spin-related phenomena and offer unique potentials for graphene-based spintronics. Here, we report the signatures of magnetism in zigzag graphene nanoribbons (zGNRs) embedded in h-BN by performing magneto-transport measurements in the ballistic regime. The in-plane bonding with BN can stabilize the edges of zGNRs, and thus enable a direct probing of the intrinsic magnetism. Fabry-Pérot interference patterns were observed in a zGNR transistor at 4 Kelvin, which indicates a coherent transport through the channel. A large magnetoresistance of ~175 Ω, corresponding to a ratio of ~1.3 %, was observed at the same temperature. Such magneto-transport signal is highly anisotropic on the magnetic field direction, and its appearance extends well above room temperature. All these evidences corroborate the existence of robust magnetic ordering in the edge state of zGNR.

报告人简介：

Dr. Wang is an experimental scientist, working in low-dimensional carbon materials and their devices. He received his Ph.D degree in the department of electrical and computer engineering of National University of Singapore in 2009. At the end of 2011, Dr. Wang was appointed as a research professor in SIMIT. His current research interest focuses on fabrication of novel low dimensional carbon materials and exploration of their transport properties. Recently, Dr. Wang made great progresses in direct growth of graphene and its nanostructures on hexagonal boron nitride, including alignment determination, gaseous catalyst assisted growth, edge control of graphene domains and fabrication of oriented graphene nanoribbons. The progresses are recognized in research community of 2D materials and shine a light on further application of 2D materials in nano-electronics and metrology in future. Dr. Wang published 69 peer-reviewed papers in scientific Journals, including Nature Materials, Nature Reviews Physics et al. and holds 31 invention patents. He was awarded the First Prize of  Shanghai Natural Science Award in 2020.

7 电极材料表面纳米层构筑及功能

报告人：曹安民，中国科学院化学研究所

时间：3月15日（周三）14:30

单位：中科院物理所

腾讯会议：120 965 326

地点：M楼253会议室

摘要：

高比能量、高安全的电化学储能技术是清洁能源发展的重要方向，电极材料的稳定性和电池的安全性成为储能器件大规模应用的关键，材料表面结构及功能对电池的稳定性、安全性具有决定性影响。本次报告将介绍我们在电极材料结构调控及稳定性提升上的近期进展，相关工作立足于高比能正极材料的表面调控工艺开发，基于液相反应过程，调控包覆物种生长动力学，实现正极粉体表面纳米层的精准构筑；同时，设计并控制表面固相反应，调控电极材料的表面物理化学特性，研究电极材料在电化学过程中的失稳机制及稳定途径，获得具有应用前景的稳定工艺及高比能正极材料。

报告人简介：

曹安民，2006年中科院化学所博士，2007年至2012年分别在美国匹兹堡大学、德州大学奥斯汀分校从事博士后研究，2012年加入中科院化学所任研究员。课题组工作聚焦于电极材料表界面调控，致力于纳米能源化学研究，获得兼具高比能、高功率、高稳定性的储能器件。代表性成果发表在Nat. Mater.、J. Am. Chem. Soc.、Angew. Chem. Int. Ed.及Adv. Mater.等国际著名杂志上，目前承担了国家杰出青年基金（2020）、重点研发计划课题、中科院前沿科学研究等项目。

8 固体电解质材料应用于固态电池体系中的关键问题与应对方案

报告人：郭向欣，青岛大学

时间：3月15日（周三）15:30

单位：中科院物理所

腾讯会议：120 965 326

地点：M楼253会议室

摘要：

固态锂电池制备的关键包括固体电解质材料、高面容量正极和锂负极材料、以及多维多尺度界面设计和电芯集成。报告基于多年对氧化物固体电解质的研究，讨论固体电解质材料在实用化进程中在离子电导率、高导通稳定电解质膜、电解质正极复合电极、电解质负极复合电极所面临的关键问题与应对方案。对基于氧化物固体电解质的固态锂电池关键界面问题进行探讨，包括电解质材料表面碳酸锂、固态复合正极内部界面、正极和电解质间界面、有机无机复合电解质膜内部界面、锂金属硅负极和电解质间界面、以及电芯界面的设计与构筑。针对面向高能量密度高安全发展目标所提出的正极支撑、轻薄固态电解质层、电极电解质一体化固化的设计思路和制备方法开展讨论。

报告人简介：

郭向欣，上海市浦江人才、山东省泰山学者特聘教授、青岛市创业创新领军人才。现为青岛大学二级教授，博士生导师，青岛市高性能固体电解质与固态锂电池研究中心和山东省固态电池工程实验室主任。主持国家自然科学基金联合基金重点项目和面上项目多项，参与国家重点研发计划新能源汽车重点专项。受聘为国家科技部和基金委项目评审专家，无机材料学报和储能科学与技术编委。研究工作聚焦固态离子导体中的离子输运与界面调控。

9 The cuprate phase diagram: theory of the pseudogap metal, dwave superconductivity, and charge order

报告人：Subir Sachdev，Harvard University

时间：3月15日（周三）16:30

单位：香港大学

会议链接：https://www.koushare.com/live‍s/room/026082

摘要：

I will begin with an introduction to the phase diagram of the hole-doped cuprates. The pseudogap metal will be described as a FL* phase of the single-band Hubbard model, with small pocket Fermi surfaces, and an underlying π-flux spin liquid with an emergent SU(2) gauge field. Such a theory provides a good description of the photoemission spectrum at intermediate temperatures. I will present a theory of the confinement transition of this SU(2) spin liquid as temperature is lowered. This theory leads naturally to d-wave superconductivity and charge order.

10 Does Dark Matter Interact with Dark Energy?

报告人：张佳骏，上海天文台

时间：3月16日（周四）10:00

单位：中科院理论物理所

会议链接：https://www.koushare.c‍om/lives/room/560764

摘要：

In the standard cosmological model, LCDM model, dark matter and dark energy are two major components. However, whether there is interaction between dark matter and dark energy beyond gravity is unknown. Together with collaborators, I have developed the simulations and related codes for interacting dark energy model. Using N-body simulation, we have studied the impact of dark matter dark energy interaction on the structure formation. Combined with observations such as CMB, BAO, weak lensing and halo density profile, we have put strong constraints on the interaction between dark matter and dark energy.

报告人简介：

Prof. Jiajun Zhang is an assiociate professor from Shanghai Astronomical Observatory, Chinese Academy of Sciences. He got his PhD from The Chinese University of Hong Kong at 2017, and he worked at Shanghai Jiao Tong University from 2017 to 2019, worked at IBS, South Korea from 2019 to 2021. He returned to China and joined SHAO at 2021. His research interests are cosmology, N-body simulation, large scale structure, radio cosmology etc. His has published more than 30 SCI papers on well-known journals such as A&A, ApJ, PRD, MNRAS etc.

11 Universal theory of strange metals

报告人：Subir Sachdev，Harvard University

时间：3月16日（周四）16:30

单位：香港大学

会议链接：https://www.koushare.com/live‍s/room/540741

摘要：

Strange metals are ubiquitous in correlated quantum materials. In limit of low temperatures (T), strange metals are characterized by a low resistivity which decreases linearly with T to values well below the Mott-Ioffe-Regel bound, a specific heat which varies as T ln(1/T), and a marginal Fermi liquid form for the electronic spectrum. We present a theory of strange metals in two dimensions which reproduces all of these features, and is also in general agreement with the frequency and T dependence of optical conductivity measurements in the hole-doped cuprates. The theory describes a Fermi surface coupled to a critical boson, the latter representing an order parameter or an emergent gauge field. We find that the key ingredient in the strange metal behavior is the presence of spatial randomness in the Yukawa coupling between fermions and the critical boson. Our solution builds on insights gained from the exactly soluble Yukawa-Sachdev-YeKitaev models of metals without quasiparticles.

12 量子多体系统的非平衡动力学

报告人：杨志成，北京大学物理学院

时间：3月17日（周五）15:00

单位：北京大学物理学院、北京物理学会

会议链接：https://www.koushare.com/lives/room/‍371889

摘要：

量子多体系统的非平衡动力学近年来成为国际上量子多体物理研究的新热点方向。这一新兴前沿以前所未有的方式沟通了传统量子多体物理、统计物理、量子信息与量子计算、原子分子物理、高能物理等诸多研究领域。本期报告将介绍量子多体系统热化、局域化、量子疤痕态、多体量子纠缠动力学等基本概念，并着重展示量子信息与统计物理等不同视角的结合对探索上述问题的重要作用。

报告人简介：

杨志成，2013年本科毕业于北京大学，2019年博士毕业于波士顿大学，2019—2022年在马里兰大学帕克分校从事博士后研究，2022年7月加入北京大学物理学院理论物理研究所。主要研究方向为量子多体系统的非平衡动力学、热化、多体量子纠缠、量子纠缠相变等。在《自然·通讯》(Nature Communications)、《物理评论快报》(Physical Review Letters)、《物理评论X》(Physical Review X)、《物理学评论X辑-量子》（PRX Quantum）等期刊发表论文20余篇。

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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