報告人：金彪，中國科學院大學
時間： 7月19日（周二）14:00
單位：中科院物理研究所
地點：M234報告廳
對自旋三重態超導的理論描述，要比自旋單態情況更為複雜。 在本講座中，將介紹自旋三重態超導微觀理論的基礎部分， 可當做對國科大開設的《固體理論》課程中超導理論部分的後繼內容。希望同學們預習好BCS 超導理論。
2Novel Semiconductor and Epitaxial Nanocomposite Materials forEnergy Conversion and Optoelectronic Applications報告人：Joshua M. O. Zide
時間： 7月19日（周二）10:00
單位：中科院物理研究所
地點：D-210
Advances in electronic materials (specifically, semiconductor and nanocomposites) enable new device technologies and improve the properties of existing technologies. In this talk, I will present efforts with in my group on the growth of new materials by molecular beam epitaxy and the resulting advance sin solar cells, thermoelectrics, and optoelectronics.
Specifically, I will discuss two material systems: (1) nanocomposites consisting of metallic nanoparticles (such as ErAs and TbAs) within III-V semiconductors (such as InGaAs and GaAs), and (2) dilute bismuthide semiconductors in which bismuth is incorporated into III-V materials to reduce the bandgap significantly, with unique band alignments that cannot be easily achieved in other materials. In these new materials, electronic, thermal, and optical properties can be quite different from those of conventional materials, with significant promise for applications in a variety of (opto) electronic devices.
3Nonadiabatic molecular dynamics investigations on the ultrafast charge dynamics at Interfaces報告人：趙瑾，中國科學技術大學
時間： 7月19日（周二）14:00
單位：北京大學量子材料科學中心
地點：北京大學物理樓，西563會議室
The ultrafast dynamics of photo-excited charge carriers plays an important in optoelectronics and solar energy conversion. Using nonadiabatic molecular dynamics simulation, we study the ultrafast charge dynamics at CH3OH/TiO2 and MoS2/WS2 interfaces. For CH3OH, we study the forward and backward hole transfer between TiO2 and CH3OH as well as the whole hole relaxation process to valance band maximum (VBM). First, we found that the hole trapping ability of CH3OH depends on the adsorption structure strongly. Only when the CH3OH is deprotonated to form chemisorbed CH3O, there will be ~15% hole trapped by the molecule. Second, we found the time scales of forward hole transfer process from TiO2 to CH3O (hole trapping process) and hole relaxation to VBM strongly depend on the temperature. When the temperature decreases from 300K to 30K, for hole trapping process, the time scale increases from 150 fs to ps magnitude. The hole relaxation process to VBM is also slow down significantly. This can be interpreted by the reduction of the non-adiabatic coupling and the phonon occupation. Our studies provide valuable insights into the photogenerated charge dynamics near molecule/TiO2 interface. For MoS 2/WS2, we show that instead of direct tunneling, the ultrafast interlayer hole transfer is strongly promoted by an adiabatic mechanism through phonon excitation. At room temperature the interlayer charge transfer in MoS2/WS2 is ultrafast with a timescale of 20 fs which is in good agreement with the experiment. This ultrafast hole transfer process can be
suppressed by decreasing the temperature to 100K, which reduces the phonon occupation and the charge transfer is then dominated by direct tunneling, which happens at the time scale longer than 300 fs. The atomic level picture of phononassisted ultrafast mechanism revealed in our study is valuable both for the fundamental understanding of ultrafast charge carrier dynamics at vdW hetero-interfaces as well as for the design of novel quasi-2D devices for optoelectronic and photovoltaic applications.
4Majorana Fermions in Ballistic Nanowire Devices報告人：Hao Zhang，Delft University of Technology
時間： 7月19日（周二）16:00
單位：北京大學量子材料科學中心
地點：物理樓西563會議室
Majorana fermions are quasiparticles predicted to show non-Abelian exchange statistics, and can be used for topological quantum computing. Following proposals for their detection in a semiconductor nanowire coupled to a superconductor, several electron transport experiments reported characteristic Majorana signatures. The prime challenge to strengthen these signatures and unravel the predicted topological properties of Majoranas is to reduce the remaining disorder in this hybrid system. Disorder not only mimics Majorana signatures, but also results in a soft induced superconducting gap. This soft-gap renders the topological properties experimentally inaccessible. Here, by eliminating disorder in our Majorana devices, we report ballistic transport behavior based on observation of a quantized conductance for normal carriers and a strong enhancement of conductance resulting from Andreev reflection. Gate tuning the device to a tunnel probe reveals an induced hard-gap. Spatial control of carrier density using local gates and an application of a magnetic field induces a zero bias peak that is rigid over a large region in the parameter space of gate voltage and magnetic field. The extracted parameter region of this zero bias peak matches with the Majorana topological phase diagram. We know of no theoretical framework other than those based on Majorana fermions that is consistent with our observations.
5Hamiltonian Analysis of Gravity in 3 Dimension Spacetime under Null Coframe報告人：孔師碑
時間： 7月20日（周三）10:00
單位：中科院高能物理研究所
地點：理論室319
The null coframe in this work is inspired by the Newman-Penrose form in 3 dimension. Connections are treated independently. Bondi-like coordinates are used in this work. Lagrangian of the gravity is acquired from the Palatini action with a cosmological constant term. Equations about the conjugate momentums are treated as primary constraints, where only one is the first class constraint. Hamiltonian is acquired from Legendre transformation of the Lagrangian. All secondary constraints and the Lagrange multiplicative factors are acquired from Hamiltonian analysis. A new first class constraint is obtained from certain combination of some primary constraints. There is no degree of freedom left in this system. Equations of motion of the canonical variables are calculated. In the end, the above results are applied to BTZ spacetime.
6Entanglement entropy fluctuation and distribution for open systems報告人：J. Wang，the University of Hong Kong
時間： 7月20日（周三）10:00
單位：北京師範大學
地點：物理樓106
Quantum entanglement is the fundamental feature in quantum mechanics which can be characterized by the entanglement entropy. The entanglement entropy generated by the quantum transport, similar to any physical observable quantity, is a stochastic variable that has its distribution and can fluctuate. In this work, we introduce the entanglement entropy operator and develop a theoretical framework to calculate the entanglement entropy fluctuation as well as its higher order cumulants generated by electronic transport in open systems. The distribution of entanglement entropy generated by opening or closing a quantum point contact (QPC) is solved exactly. In the presence of bias, eigenvalues of entanglement entropy of a QPC are obtained analytically in the long time limit and the distribution of entanglement entropy is found to obey a modified binomial distribution. When the transmission coefficient of QPC is one half, the entanglement entropy is maximized and fluctuationless. We also provide a relation between the generated entanglement entropy fluctuation and charge fluctuation. We apply our theory to electronic transport through a quantum dot (QD) and study the generated entanglement entropy in the transient regime. Universal behavior is found for the cumulants of entanglement entropy at short times.
7Climate network suggests enhanced El Ni~no global impacts in localized areas報告人：Jing-fang Fan，Department of Physics Bar-Ilan University
時間： 7月20日（周三）15:00
單位：中科院理論物理研究所
地點：ITP New Building 6420
We construct directed and weighted climate networks based on near surface air temperature to investigate the global impacts of El Ni~no and La Ni~na. We nd that regions which are characterized by higher positive/negative network \in"-weighted links (i.e., exhibiting stronger correlations with El Ni~no basin) are warmer/cooler during El Ni~no/La Ni~na periods. These stronger in-weight activities are found to be concentrated in localized areas compared to non El Ni~no periods, whereas a large fraction of the globe is not influenced by the events. The regions of localized activity vary from one El Ni~no (La Ni~na) event to another, but still some El Ni~no (La Ni~na) events are more similar to each other. We quantify this similarity using network community structure. The results and methodology reported here may be used to improve the understanding and prediction of El Ni~no/La Ni~na events and also may be applied to investigate other climate variables.
8F-theory and Particle Physics報告人：Mirjam Cvetic，University of Pennsylvania
時間： 7月20日（周三）15:00
單位：中科院理論物理研究所
地點：ITP New Building 6620
We present developments in F-theory compactifications with an emphasis on particle physics implications. We spell out techniques to construct globally consistent F-theory compactifications that result in particle physics models, such as the SU(5) GUT's and the first three family Standard Model construction. We also spell out technical advances in constructions of F-theory compactifications with higher rank Abelian and discrete symmetries.
9Gauged STU Supergravity from 11 Dimensions報告人：Chris Pope，Texas A&M University
時間： 7月20日（周三）16:00
單位：中科院理論物理研究所
地點：ITP New Building 6620
The way in which gauged supergravities can be embedded in higher-dimensional supergravities by means of dimensional reductions on spheres is highly non-trivial. We begin by reviewing some of the key ideas involved in Kaluza-Klein reductions, with a particular emphasis on the crucial issue of the consistency of the reduction. This is essential in order to ensure that the lower-dimensional theory is a true embedding, such that solutions in the lower-dimensional theory lift to solutions of the higher-dimensional theory. We will show in generic theories, dimensional reductions on spheres will not be consistent, and then we will show how particular supergravities evade such no-go theorems. We then turn to the specific case of the 7-sphere reduction of eleven-dimensional supergravity, which was shown by de Wit and Nicolai to give N=8 gauged SO(8) supergravity in four dimensions. We then report on our recent work, where the rather complicated expressions for the full N=8 reduction become considerably simpler in the truncation to N=2 gauged U(1)^4 STU supergravity. The embedding we obtain is sufficient for lifting most known solutions of four-dimensional gauged supergravity to eleven dimensions.
10Exploration of Parameter Redundancy and Compression in Deep Neural Networks報告人：Yu Cheng，IBM T.J. Watson Research Center, USA
時間： 7月22日（周五）15:00
單位：中科院理論物理研究所
地點：ITP New Building 6420
Compressing Deep Neural Networks has has attracted a lot of attention recently. In this talk, we will discuss several of our previous and current work about parameter redundancy in deep convoluational nets. Particularly, the talk focuses on how to use structure transformation to reduce parameters and how to design efficient architecture in deep nets. We will show intensive empirical studies on several standard datasets to demonstrate the effectiveness of our approaches.