非铅钙钛矿纳米晶载流子动力学 | 本周物理学讲座

来源：中国物理学会期刊网

1非铅钙钛矿纳米晶载流子动力学

报告人：韩克利，大连化物所研究员

时间：10月29日（周二）15:00

单位：北京大学

地点：物理楼西楼464

含铅钙钛矿纳米晶CsPbX3（X=Cl，Br，I）具有吸光系数大，发光量子产率高，带隙易调节等优点，因此被广泛研究于发光二极管（LED）、纳米激光器、太阳能电池以及光电探测器等方向。然而其中含有的重金属元素铅对环境和人类造成危害，限制了其商业化应用。寻找无毒且性能好的非铅钙钛矿成为当下的研究热点和难点。我们采用超快光谱等技术系统研究了一系列非铅钙钛矿纳米晶材料的载流子动力学。研究发现非铅钙钛矿纳米晶中存在超快的激子捕获过程，进而发生非辐射复合，是限制其发光效率的关键因素。通过调节其自缺陷态及钝化表面缺陷态，可提升发光效率100多倍。

2Performance of a full EM p of the CMS High Granularity Calorimeter: October 2019 results

报告人：Stathes Paganis，National Taiwan University

时间：10月30日（周三）10:00

单位：中科院高能物理所

地点：B326 Main Building

The CMS HGCAL EM calorimeter is a state-of-the-art 28-layer sampling calorimeter with Si sensors as the active material. IHEP is setting up a facility to build the heart of the calorimeter: the modules, an assembly of electronics, sensors and passive material. In 2018, a full p of this device with prototype electronics has been put in a CERN testbeam. The latest results are presented and compared to expectations with simulation. Our experience is relevant to the design choice for the EM calorimeter for CEPC, where the requirements are not identical to the LHC phase-II. Benefits to the community by building such a device in-house are also discussed.

3LHAASO Status and First Results

报告人：Zhen Cao，the Institute of High Energy Physics

时间：10月31日（周四）16:00

单位：清华大学

地点：理科楼郑裕彤讲堂

The Large High Altitude Air Shower Observatory (LHAASO) as the largest ground based Gamma Ray detector array is under construction. The first 1/4 array with the coverage of 1/4 km2 has been put in operation for science. It has an array of 1314 scintillator counters and 304 muon detectors in the array nearby a Water Cherenkov Detector with an active area of 22500 m2. The size of the array is still growing rapidly. By the end of this year, 1/2 of the array will be turned on for scientific operation. The construction of the entire array will be concluded in next year. Finding the galactic Cosmic Ray (CR) origin has been set as the goal of the mega project, by surveying for the gamma ray sources and precisely measuring the gamma ray spectra of them up to 1 PeV. Many related scientific questions can be addressed with the experiment using LHAASO. Preliminary results of the analysis of data taken by the first quarter of array and expectations are presented.

4 First binary black hole coalescences

报告人：Kohei Inayoshi，The Kavli Institute for Astronomy and Astrophysics

时间：10月31日（周四）16:00

单位：北京大学

地点：KIAA-PKU Auditorium

The direct detections of gravitational waves (GWs) by Advanced LIGO/Virgo have opened a new era in astronomy. The discovery of an unexpected population of massive binary BHs (BBHs) constraints their formation pathway and requires massive star formation in low-metallicity environments. In this talk, I discuss low-metallicity massive star formation in the early universe, so called Population III stars (PopIII stars), and binary evolution of massive PopIII stars into colliding BBHs. Intriguingly, PopIII binary model can explain the natures of coalescing BBHs observed by LIGO/Virgo, in terms of the merger event rate and BH mass distribution. A majority of the first binary BHs form and merge in the early universe. We have suggested that such individually unresolved GWs develop a GW background, which would be detectable by O5 LIGO/Virgo observation. More interestingly, the BH population producing the GW background will also be probed by the observations of the cosmic microwave background, on which stellar activities of the first stars are directly imprinted. 

5Linear Raman and Coherent Anti-Stokes Raman Spectroscopy of II-VI Semiconductor Quantum Dots5145508053308428/20191025145508053308428_.html

报告人：W. Kiefer，University of Würzbur

时间：11月1日（周五）14:00

单位：中科院半导体研究所

地点：2号楼303A会议室

6Spatiotemporal Dynamics of Optical Pulse Propagation in Multimode Fibers

报告人：Frank Wise，Cornell University

时间：11月1日（周五）14:00

单位：清华大学

地点：物理系理科楼C109

Optical fibers designed to support multiple transverse modes offer opportunities to study wave propagation in a setting that is intermediate between single-mode fiber and free-space propagation.

A variety of qualitatively-new phenomena have been observed recently in multimode fibers. Self-cleaning of a multimode beam is observed at a fraction of the critical power for self-focusing, and without loss [1,2]. New instabilities, which are spatiotemporal in nature, occur [3,4,5]. By varying the launched spatial modes, it is possible to generate dispersive waves over an octave in frequency, megawatt pulses in the near infrared, or continua that span multiple octaves [6]. After a tutorial introduction to nonlinear wave propagation,>Synchronization of transverse and longitudinal modes – spatiotemporal mode-locking – of a multimode fiber laser was recently demonstrated [7]. The basic features of spatiotemporal mode-locking and recent progress in theoretical understanding will be presented. The variety of 3-dimensional lasing states appears to open many opportunities for future study.

7High pressure studies in iron-based compounds and recent study of pressure-induced superconductivity in iron-based spin-ladder material

报告人：Hiroki Takahashi，Nihon University, Japan

时间：11月1日（周五）10:00

单位：中科院物理研究所

地点：物理所M楼253

Iron-based superconductor is well known as a high-Tc superconductor, which has a two-dimensional iron lattice and exhibits characteristic magnetic phases next to the superconducting phase. Large enhancement of Tc under pressure was found in the iron-based superconductor in the early stage. Our group reported some exciting results using high pressure technique. The technique will be presented in this talk. A diamond anvil cell was used mainly to generate high pressure. However, a cubic anvil press has advantage to generate hydrostatic pressure. 

Among the study of the iron-based superconductor, we have an interest in iron-based ladder-type compound, which exhibits various kinds of magnetic ordering phase. They are one-dimensional analog of both stripe and block magnetism related to the iron-based superconductors. In these compounds, we discovered the pressure-induced superconductivity in the spin-ladder compound BaFe2S3 which exhibits the stripe magnetism at atmospheric pressure. With applying pressure, the insulator-metal transition was observed at ~11GPa, and just after appearance of metallic phase, superconductivity was observed. The dome-shaped superconducting phase was obtained in the P-T phase diagram, in which the maximum Tc was 17 K. We also studied the spin-ladder compound BaFe2Se3 which exhibits the block magnetism at atmospheric pressure. Although pressure-induced superconductivity was already found for BaFe2Se3 by other group, the interplay between superconductivity and magnetism remains open question. We confirmed the sudden drop in electrical resistivity for BaFe2Se3 under high pressure which is thought to be caused by superconductivity and studied the relation between magnetic ordering temperature TN and superconductivity by changing the content of excess Fe.

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