高效率准二维钙钛矿发光二极管的激子调控 ｜ 本周物理

　　1高效率准二维钙钛矿发光二极管的激子调控

　　报告人：秦川江，中国科学院长春应用化学研究所

　　时间：11月26日（周二）9:00

　　单位：北京大学

　　地点：物理楼西楼464室

　　有机无机杂化钙钛矿因成本低、容易加工以及光电特性优异，受到了光电子研究领域的广泛关注，基于该类材料的发光二极管也极具潜力成为下一代照明和显示元件。由于准二维钙钛矿存在天然形成的量子阱结构，与传统的三维钙钛矿相比具有更大的激子结合能，从而更有利于发光。与典型的无机半导体不同，有机半导体在电致发光过程中首先形成激子态而后弛豫发光。由于电子的自旋特性，将会形成单线态和三线态两种不同性质的激子。尽管调控单线态和三线态激子是设计和开发高效有机发光二极管的基础，但在钙钛矿发光二极管的研究中却仍未被考虑。在本研究中，我们比较了两类具有相似晶体性质，但含有不同有机组分的钙钛矿发光材料，发现其中一类钙钛矿材料中的三线态激子消失了。通过分析发现这类钙钛矿中采用了具有低三线态能级的有机组分，其发光性能能差的原因应是三线态激子转移至能量较低的有机部分，造成非辐射能量损失。而当采用具有高三线态能级的有机组分时，三线态激子会保留在钙钛矿发光主体中，从而获得高的发光效率。此外，我们进一步证实在特定的准二维钙钛矿中，暗态三线态激子也能够上转换为辐射发光的单线态激子，使得在准二维钙钛矿器件中实现全部激子利用成为可能。基于上述发现，通过选择合适的有机组分，我们制备了能够高效俘获三线态激子的准二维钙钛矿发光二极管，获得了12.4%的电光转换效率。

　　2宇宙学与诺奖的恩怨纠葛

　　报告人：郭宗宽，中科院理论物理所

　　时间：11月26日（周二）12:00

　　单位：中科院理论物理所

　　地点：ITP South Building 6420

　　普林斯顿大学教授詹姆斯·皮布斯，在宇宙学理论方面做出了杰出贡献，分享了2019年度诺贝尔物理学奖。报告将回顾宇宙学的发展历程，讲述宇宙学与诺奖的恩怨纠葛，解读2019年度诺贝尔物理学奖。

　　3Next-generation optoelectronic devices with metal halide hybrid perovskites

　　报告人：Toshinori Matsushima，Kyushu University, JAPAN

　　时间：11月26日（周二）10:00

　　单位：北京大学

　　地点：物理楼西楼464室

　　Metal halide perovskites are promising for use in many optoelectronic devices because perovskites show efficient emission and have bandgap tunability, high carrier mobility, and long carrier diffusion even in polycrystalline films fabricated with low-cost solution processing. First I discuss our recent results of hybrid perovskite-based devices, which include solar cells, light-emitting diodes, field-effect transistors, and laser devices. In transistors with large perovskite crystals, we obtained very high hole and electron mobilities of 50-100 cm2/V s, along with excellent air and bias stability. Next, we introduce organic light-emitting diodes, in which perovskites are used as host or carrier transport layers. With perovskite transport layers, we demonstrated that device thickness was increased by more than ten times without increasing driving voltage and decreasing external quantum efficiency or operational durability and that our two-micrometer-thick devices had very high external quantum efficiencies of ~40%. The energy transfer from a perovskite to an organic emitter overcame the singlet generation efficiency limit 25% for fluorescent organic light-emitting diodes, opening a way to the fabrication of higher-performing devices at a lower cost in the future.

　　4Uniform asymptotic approximation and the non-adiabatic evolutions of primordial perturbations

　　报告人：朱涛 ，浙江工业大学理论物理与宇宙学研究所

　　时间：11月26日（周二）15:30

　　单位：北京师范大学

　　地点：物理楼106

　　The second-order ordinary differential equation (sODE) has been involved in a lot of branches of theoretical physics, and the Jeffreys-Wentzel-Kramers-Brillouin (JWKB) method is one of the most powerful approximation to this type of equation with great success. However, the validity of the JWKB method has to be restricted to the region where the JWKB condition (or adiabatic condition) is fulfilled. Recently, we developed a powerful and effective method, the uniform asymptotic approximation, to accurately construct analytical solutions of sODE. The most remarkable feature of this method is that it provides a systematic and error controlled treatment to regions where the adiabatic condition is violated, and goes over to the JWKB approximations when the adiabatic condition is restored. In this talk we are going to provide a brief introduction about the uniform asymptotic approximation and its recent applications to study the non-adiabatic effects on primordial perturbations. Applications to several other problems in quantum mechanics, black hole physics, and loop quantum cosmology have also been discussed.

　　5固态放热相变激活的非晶合金点燃

　　报告人：闫志杰，中北大学材料科学与工程学院

　　时间：11月26日（周二）14:00

　　单位：中科院物理所

　　地点：D楼210会议室

　　实验发现，非晶合金具有比熔点低的燃点，其点燃机理与传统的金属材料燃烧不同，是固态放热相变激活的点燃。虽然非晶合金在不同加热速率下的晶化放热焓不变、而且是一个较小的数值，但当加热速率增大时，单位时间、单位质量的合金的放热焓（定义为比功率）急剧增大。正是这个急剧放大的固态放热比功率触发了固态连锁放热反应，结果激活了非晶合金的点燃。

　　6InP/InAs Heterostructure Nanowires towards Telecom-band Optoelectronic Devices

　　报告人：Guoqiang Zhang （章国强），NTT Basic Research Laboratories and NTT Nanophotonics Center，NTT Corporation， Kanagawa，Japan.

　　时间：11月26日（周二）10:00

　　单位：中科院物理所

　　地点：M楼249会议室

　　One motivation for the very intense research in III-V compound semiconductor nanowire field is that nanowire structures can offer new opportunities to main-stream semiconductors. In this talk, firstly, I will describe a CMOS-compatible synthesis approach, i.e. gold-free indium-particle-catalyzed (or self-catalyzed) vapor-liquid-solid growth mode. The approach enables the growth of InP/InAs heterostructure nanowire and lasing in telecom band at room temperature. We have also realized mid-IR lasing by using InAs nanowires with hexagonal crystalline structure. Controllable formation of p-i-n structure along the axial direction enables light emitting diodes to operate at room temperature with telecom-band electroluminescence. A novel approach will then be described for site control of indium nanoparticle by self-assembly process for InP/InAs nanowire array. Finally, I will describe an exceptional growth phenomenon in self-catalyzed vapor-liquid-solid mode that the catalyst particle size can be continuously tailored by modulating III-V source flow ratio.

　　7A New Anomaly in 2D Conformal Field Theory

　　单位：中科院理论物理所

　　地点：ITP South Building 6420

　　Discrete symmetries do not have Noether currents, therefore how to detect the global anomaly is not obvious. In this talk we will introduce a new global anomaly for internal discrete symmetry in 2d CFTs and compute the anomaly using torus partition function with symmetry line insertions. We compare our anomaly free condition with orbifolding condition and symmetry invariant boundary state condition by focusing on minimal models and Wess-Zumino-Witten models.

　　宇宙观测数据显示，小尺度暗物质晕的实际中心质量密度明显低于模拟计算所得出的结果，这种质量不足被认为可以通过赋予暗物质之间较强的非引力自相互作用来解释。该报告将在提出新自相互作用模型的基础上，引入一种对此类暗物质模型普适，并适用于数值模拟的参数化方法。这里的新模型包括假设暗物质之间发生共振碰撞，或者引入“荷半径”远大于其康普的波长的复合粒子，来获得碰撞散射截面的速度相关性。这些可能性或许会给暗物质粒子的理论设想带来新的启示。

　　9Vacuum structure and origin of color confinement in QCD

　　报告人：Dmitriy G. Pak，Uzbekistan National University，PIFI fellowship(中科院国际人才计划)

　　时间：11月28日（周四）15:30

　　单位：中科院理论物理所

　　地点：ITP South Building 6620

　　A long-standing problem of explicit microscopic description of a stable vacuum in a pure SU(3) quantum chromodynamics (QCD) is resolved on a basis of stationary solutions possessing local quantum stability against vacuum gluon fluctuations. A space of such solutions is factorized into two gauge and Lorentz invariant subspaces corresponding to non-Abelian color magnetic and electric type fields respectively. Each subspace contains solutions which represent fixed points under the action of the Weyl color group. Such a symmetry allows to define classical colorless gauge potentials and a space of color singlet one-particle quantum states. We show that the the origin of color confinement phenomenon or spontaneous symmetry breaking is encoded in the structure of the gauge group SU(N). The Weyl symmetric solutions manifest an Abelian dominance phenomenon in the vacuum structure and provides a consistent classification of physical states, i.e., pure glueballs. As an example, we construct a spectrum of lightest scalar glueballs. Implications in quantum gravity are discussed.

　　10How to dress a metal

　　Space-periodic arrangement of lattice ions in crystalline solids defines the k-momentum dispersion of electronic quasiparticle bands. Light can interrogate such bands by stimulating electronic dipole transitions, however, when its time-periodic interaction exceeds all other perturbations, particularly at an optical resonance, it can manipulate the system eigenstates causing the crystal band structure to be dressed. The electronic bands become replicated by Floquet engineering, and are shifted by the AC Stark effect. I will describe how we control optical fields with attosecond precision to instantaneously shift and modify electronic bands of Cu(111) surface on sub-optical cycle time scales. I will demonstrate entanglement between optical fields and k-dispersions that can modify and control the quasiparticle properties, such as band energies and transport masses, and therefore, all electronic properties that depend on them. I will also explore the possibility to design and control the quasiparticle properties of quantum materials by light. The chemical interactions that establish the crystalline band structures no longer limit the properties of electronic materials, but they can be modified on demand by light.

　　11The Advent of Two-dimensional Materials

　　报告人：张远波，复旦大学

　　时间：11月29日（周五）14:00

　　单位：中科院物理所

　　地点：M楼234

　　Two-dimensional (2D) atomic crystals, best exemplified by graphene, have emerged as a new class of material that may impact future science and technology. 2D materials provides vast opportunities both on novel material properties that are different from those in the bulk, and better control of their material properties with external perturbations. In this talk I will illustrate a few examples ranged from semiconductors and high temperature superconductors. In particular, black phosphorus is a 2D semiconductor, and its superior material quality has recently enabled us to observe the quantum Hall effect; others include magnetic topological insulator and high temperature superconductor Bi2Sr2CaCu2O8+？in the 2D limit. We explore their electronic properties while the doping and dimensionality of the 2D systems are modulated.

　　12面向计算中心运维任务的异常检测

　　时间：11月26日（周二）15:00

　　单位：中科院高能物理所

　　地点：计算中心二楼会议室

　　目前，智能运维是人工智能、行业领域知识、运维场景领域知识三者相结合的交叉领域，问题场景包括容量管理、异常检测、故障修复等。

　　此次报告将首先大体介绍一下智能运维的整体框架，而后主要聚焦面向计算中心运维任务的异常检测问题，将详细介绍不同的异常检测方式，以及各方法针对Lustre元数据服务器的效果展示和分析。

　　13The Genesis of General Relativity and its Consequences

　　报告人：哈诺赫·古特弗罗因德，耶路撒冷希伯来大学

　　时间：11月26日（周二）16:00

　　单位：中科院理论物理所

　　地点：中科院自然科学史研究所学术报告厅

　　14QCD basis of low energy effective Lagrangian

　　15Optical Response of Two-Dimensional Crystals

　　报告人：Jun Yan，Department of Physics, University of Massachusetts Amherst, MA USA

　　时间：12月2日（下周一）14:00

　　▼往期精彩回顾▼

　　1.宇宙中元素的起源

　　2.“量子霸权”来了，中国如何发力