铁基超导体中自旋共振模的对称性 | 本周物理学术讲座

1铁基超导体中自旋共振模的对称性  

报告人：罗会仟，中科院物理所

时间：9月13日（周四）15:00

单位：北京师范大学物理学系

地点：物理楼106

磁相互作用在铁基超导电性形成中至关重要，最典型特征就是自旋共振模——低能磁激发会出现超导序参量式的响应，被认为是费米面嵌套下符号相反的s波配的重要证据。然而自旋共振的能量-动量分布、色散关系、空间各向异性等特征却与理论预言存在较大的差异。我们最近利用非弹性中子散射研究了新型铁基超导体Ca1-yLayFe2-xNixAs2和CaKFe4As4体系中的自旋共振模，确认在自旋轨道耦合较弱情形下自旋共振模在自旋空间是各向同性的，多个超导配对通道下会产生多重共振模，并因其c方向耦合造成奇数或偶数L调制结构。自旋共振能与临界温度、嵌套费米面总超导能隙等呈线性标度关系，并与与铜基高温超导和重费米子超导材料存在相似性。

2Synthetic topological defects and synthetic spaces in ultracold atoms

报告人：Qi Zhou, Purdue University

时间：9月12日（周三）10:00

单位：中科院物理研究所

地点：M830

In this talk, I will discuss how to engineer laser-atom interactions for creating synthetic topological defects and synthetic spaces. Engineered couplings between internal states of ultracold atoms have allowed experimentalists to deliver a Yang monopole in laboratories. I will show that interactions lead to topological defects beyond the descriptions of single particle physics. Discrete defects may even be turned into continuous ones, a new type of “more is different” phenomena.  If time allows, I will discuss a recent progress towards creating synthetic curved spaces.

3Two indices Sachdev-Ye-Kitaev model 

报告人：Jinwu Ye，首都师范大学

时间：9月12日（周三）14:30

单位：中科院理论物理研究所

地点：Conference Room 322, ITP main building

We study the original Sachdev-Ye (SY) model in its Majorana fermion representation which can be called the two indices Sachdev-Ye-Kitaev (SYK) model. Its advantage over the original SY model in the $ SU(M) $ complex fermion representation is that it need no local constraints, so a $1/M $ expansion can be more easily performed. Its advantage over the 4 indices Sachdev-Ye-Kitaev (SYK) model is that it has only two site indices $ J_{ij} $ instead of four indices $ J_{ijkl} $, so it may fit the bulk string theory better. 

4Low dimensional hybrids and their novel gate-tunable quantum properties

报告人：韩拯，中国科学院金属研究所

时间：9月12日（周三）16：00

单位：北京大学量子材料中心

地点：物理楼西563会议室

Electrostatic gate tuning of quantum properties has been the key of mesoscopic physics. Especially,when the thickness of a system become negligible (i.e., the 2D limit), Coulomb screening is strongly suppressed and thus gate tuning can directly affect/shift its Fermi level, leading to a tremendous variety of emerging phenomena.In this talk, we will first go through our previous works on quantum properties of the 2D materials/hBoron-Nitride nano-hybrid systems.Our recent studies on the electro-static gate tuning of an intrinsic ferromagnetic semiconductor in the 2D limit will also be discussed. We expect that artificial nano-hybrids and their quantum properties can be expanded into many research areas that are important for both fundamental studies and future applications.

5Alternative battery concepts beyond “standard Li-ion”: Examples on sodium-ion batteries, solid-state batteries and a surprise on sulfur

报告人：Philipp Adelhelm 

时间：9月13日（周四）10：30

单位：中科院物理研究所

地点：D210会议室

The rising demand for rechargeable batteries for electric vehicles and grid storage applications causes a lot of interest on alternatives to “standard Li-ion battery technology”. Major motivations are also directed towards using more low cost components and/or improving safety. Important concepts that are currently studied are sodium-ion batteries, solid state batteries as well as metal-chalcogen batteries (metal-oxygen and metal-sulfur).

6Star Formation, Gas, and Dust in CANDELS Galaxies

报告人：Sandra Faber，UCSC

时间：9月13日（周四）14:00

单位：清华大学物理系

地点：蒙民伟科技南楼S727

The CANDELS survey on the Hubble Space Telescope has produced high-quality photometric information from the far-UV to the near-IR that can be used to measure star-formation rates and reddening. This talk will compare the CANDELS star-formation rates to IR values and summarize the variation versus redshift, stellar mass, and galaxy radius. The resulting rates will then be used to deduce total gas content using the Schmidt-Kennicutt law. Dust predictions are generated from these gas masses, which are then compared to observed reddening from the SEDs. Much more dust is predicted than inferred from SED reddening. The discrepancy can be resolved if most of the dust is sequestered in small, dense clumps and therefore has little effect on the integrated light.

7The Radiation Mechanism of Fast Radio Bursts

报告人：Wenbin Lu，California Institute of Technology

时间：9月13日（周四）16:00

单位：北京大学科维理天文与天体物理研究中心

地点：KIAA-PKU Auditorium

Fast radio bursts (FRBs) are bright millisecond-duration transient events, first detected at ~GHz frequencies by the Parkes Telescope. There are about ten thousand bright (> 1 Jy ms) FRBs per day coming from random directions across the entire sky. One source discovered by the Arecibo Telescope, FRB 121102, was found to generate numerous bursts. This allowed follow-up observations to pin-point its host galaxy, which is at a distance of ~1 Gpc. The high brightness temperatures (> 1e35 K) of FRBs mean that the emission process must be coherent. We use the observed properties of the repeater FRB 121102 to constrain the plasma conditions for a wide variety of coherent emission processes.

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