学术交流

seminar(37)

报告题目: 低温超导探测器:原理、应用和我们的实验进展

  报告人:      韦联福教授
                       西南交大物理学院和中山大学理工学院教授
  地    点:     物理楼1楼会议室111
  时    间:     2012年11月22日(星期四) 下午2:00

摘    要: 由于低温超导材料的超导能隙比半导体能隙低三个数量级,所以低温超导辐射探测器的灵敏度将至少高于目前性能最好的半导体探测器一个数量级以上。本报告将在简要介绍低温超导辐射灵敏探测的原理、实现方式及其在量子信息和宇宙学实验中应用的基础上,具体汇报我们小组最近在低温超导谐振探测器的制作、测试和应用于固态量子计算方面的理论和实验工作。

报告人简介:韦联福博士,1998年在西南交通大学获博士学位;先后在中科院微系统所、上海交大物理系、日本理化学研究所等单位从事量子物理和量子信息处理的理论研究;现任西南交大物理学院和中山大学理工学院教授,已发表SCI收录论文八十多篇,被SCI他引七百多次;主持科技部973课题、基金委重大研究计划和自然科学基金面上等科研项目多项;目前主要研究兴趣是,基于单光子技术的光学量子信息处理和低温超导探测器及其应用于固态量子信息和宇宙学探测等方面的理论和实验研究。


seminar(36)

New insights into nanomagnetism by spin-polarized scanning tunneling
microscopy and spectroscopy
Hirofumi Oka
Max-Planck-Institut fur Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany

Abstract:
Spin-polarized scanning tunneling microscopy (SP-STM) allows imaging and spectroscopic characterization of nanostructures with unsurpassed spatial resolution. We present results by SP-STM, where we investigate the correlation between structural, electronic, and magnetic properties of individual nm small Co islands with several hundred to thousands of atoms. We use external magnetic fields of up to 4 T to tune the magnetic state of both tip and sample, and we extract the corresponding change of the differential conductance of the tunnel junction.

A recent example is our measurement of magnetic hysteresis loops ofindividual Co islands on Cu(111) at 8 K. We find switching fields of up to 2.5 T for islands with roughly 8,000 atoms. The analysis of the energy barrier of magnetization reversal from measurements of the switching field suggests a crossover of the magnetization reversal mode with increasing island size around 7500 atoms from coherent rotation to domain wall formation. [PRL 108, 107206 (2012)]

We also exploit the high spatial resolution of SP-STM in magnetic fields to measure maps of the differential conductance within a single nm-small Co island. In connection with density functional theory calculations we demonstrate for the first time that the spin polarization is not homogeneous but spatially modulated within the Co island. We ascribe the spatial modulation of the spin polarization to spin-dependent electron confinement effect within the Co island. [Science 327, 843 (2010)]
 

地点:物理楼10楼会议室1014
时间:2012年10月30日(星期二) 上午10:00


seminar(35)

报告题目: Generation of edge states at an armchair-graphene open boundary and nanoribbons
  报告人: 朱仲夏 教授
                台湾新竹交通大学电子物理系
  地点:        物理楼1楼会议室111
  时间:        2012年10月26日(星期五) 下午1:30

摘要:We demonstrated that edge states can be generated by an edge-potential at an armchair-graphene open boundary. The edge states are shown not of the same physical origin as the Tamm states in semiconductors. Pseudospin flipping is found to be the key process leading to the formation of these edge states. At an open boundary, the edge potential is shown to turn on pseudospin-flipped (intravalley) scattering even though there is no obvious breaking of the AB site (basis atoms) symmetry. For a valley-polarized incident beam, the interference between the pseudospin-conserving (intervalley) and nonconserving (intravalley) processes lead to a finite out-of-plane pseudospin density. This same mechanism leads to the edge state formation in the evanescent regime. Discussion will also cover armchair-graphene nanoribbon on the energy gap opening and the conductance.

Ref.  C.H. Chiu and C.S. Chu, Phys. Rev. B 85, 155444 (2012)


seminar(34)

拓扑绝缘体的输运性质研究

高波 研究员

中科院上海微系统与信息技术研究所

摘要

We have focused on the synthesis of bismuth based topological insulators using a vapor-solid growth method and on the magneto-resistance measurements of these materials.  Our results strongly suggested the existence of topologically protected two dimensional electron gas on sample surface.

We first explored the emergence of linear magnetoresistance in thin Bi2Se3 sheets upon tuning the carrier density using a back gate. With increasingly negative gate voltage, a pronounced magnetoresistance of ~100% is observed, while the associated B-field dependence changes from quadratic to linear. Concomitantly, the resistance-versus-temperature curves evolve from metallic to semiconductor-like, and increasingly strong weak anti-localization behavior is manifested. Analysis of the magnetoresistance data reveals two contributions, namely from the bulk conduction band and from a state inside the bulk gap. The latter is responsible for the linear magnetoresistance and likely represents the topologically protected surface state.

We also synthesized single-crystalline Bi2Te2Se nanoplates with thicknesses between 8 and 30 nm and lateral sizes of several micrometers using a vapour-solid growth method. Angle-dependent magnetoconductance measurements on individual nanoplates revealed the presence of a two-dimensional weak anti-localization effect. In conjunction with gate-dependent charge transport studies performed at different temperatures, evidence was gained that this effect originates from the topologically protected surface states of the nanoplates.


时间:9月26日上午10:30
地点:物理楼10楼会议室1014


seminar(33)

报告题目: Quantum Open Systems: Stochastic Viewpoint
报告人: 景俊 副教授
         上海大学物理系
         Research Associate, Physics Department
         Stevens Institute of Technology, Hoboken, NJ, USA
地点:物理楼1楼会议室111
时间:2012年9月21日(星期五) 下午14:00

摘要:Quantum dynamics of open systems is a generic paradigm that has been widely discussed in research fields ranging from atomic and optical physics to condensed matter physics and to quantum information science. It becomes  clear that a deep understanding of the effects of environments on a quantum  system such as the mechanisms of decoherence and the dynamics of entanglement in the framework of quantum open systems is both of fundamental interest in quantum foundation issues and of practical importance in quantum information sciences. The mastery of quantum coherence and entanglement control is the key to the success of quantum design and engineering.

In this talk I will present highlights of our recent work on several key issues in stochastic dynamics of non-Markovian quantum systems including many-body dynamics, quantum control and quantum diffusive dynamics.


seminar(32)

Imaging Spin Dynamics in Magnetic Nanostructures

Dr. X. M. Cheng (程雪梅)
Department of Physics, Bryn Mawr College

Spintronics, an emerging technology that exploits electron spin and its associated magnetic moment as well as electron charge, is an exciting and challenging area of nanotechnology. Spintronic devices, combining the advantages of magnetic materials and semiconductors, are likely to be stable, fast and capable of non-volatile data storage as well as being energy-efficient. Magnetic nanostructures, a crucial element to spintronics, have been the subject of extensive studies. Direct imaging of the magnetic configuration and spin dynamics in these magnetic nanostructures is especially important to the development of Spintronics.
In this talk I will present imaging studies of the magnetic dynamics in nanostructured materials using two different methods: time-resolved photoemission electron microscopy and magneto-optical Kerr effect microscopy. Magnetic images obtained using these methods have provided critical information for understanding magnetic vortex dynamics in micron and sub-micron scaled magnetic disks and unusual antisymmetric magnetoresistance in Pt/Co/Pt trilayers with a confined straight domain wall.


时间:6月19日下午3:00
地点:10楼会议室


seminar(31)

Surface dynamics on TiO2 single crystal surfaces and thin films

Dr. Yingge Du (杜英歌)

Environmental Molecular Sciences Laboratory, USA


Titanium dioxide (TiO2) has been extensively studied as a catalyst for a variety of potential applications, and there is a specific need for fundamental studies to address how adsorbates interact with TiO2 surfaces, and how we can tailor their structures to better harvest the catalytic and photocatalytic properties.

In the first part of this talk, I will present our scanning tunneling microscopy (STM) studies of H2O, O2, and their interactions on rutile TiO2(110) surfaces under ultra-high vacuum. By tracking the same surface area before and after molecule exposure, we study the adsorption, dissociation, diffusion, and reaction processes. We show that additional information can be derived by comparing the STM results with ensemble-averaged techniques such as temperature programmed desorption (TPD) and electron stimulated desorption (ESD). The experimental results are also compared with density functional theory (DFT) calculations for a better understanding of the reaction mechanisms. In the second part, I will present our efforts in the growth and characterization of pure and doped anatase TiO2 thin films prepared by molecular beam expitaxy. Structural excellent, epitaxial anatase TiO2(001) films with (4x1) surface reconstructions are grown on Nb doped SrTiO3(001) substrates. While pure anatase thin films are photoactive in the UV region, we show that controlled nitrogen doping can effectively extend the photo activity to the visible region.

时间:6月4日下午3:00点
地点:10楼会议室


seminar(30)

Introduction to Complex Plasmas: Experiments on ground and on board the International Space Station

(地面以及国际空间站上的尘埃等离子体实验)


Cheng-Ran Du (杜诚然)

Max Planck Institute for Extraterrestrial Physics, Garching, Germany

3月23日(星期五) 1:30, 物理楼1014室

Abstract

A complex plasma is a weakly ionized gas containing charged micrometer-sized particles. It has several remarkable features: Dynamical time scales associated with particles are ‘stretched’ to tens of milliseconds, yet the particles themselves can be easily visualized individually using video microscopic techniques. Furthermore, since the background gas is dilute, the particle dynamics in a strongly coupled complex plasma is virtually undamped, which provides a direct analogy to regular liquids and solids in terms of the atomistic dynamics. These features give us a unique opportunity to go beyond the limits of continuous media and study various generic processes occurring in liquids or solids at kinetic level. In the talk, I will introduce several representative experiments of complex plasmas performed either on ground or on board the International Space Station.
 


seminar(29)
凝聚态物理学术报告会

告题目:Nanofibers and nanowires for flexible solar cells and electronics

 报告人:Dr. Peyman Servati
Department of Electrical and Computer Engineering, University of British Columbia

 摘要
Low temperature deposition of electronic materials on unconventional flexible substrates such as plastic and paper is promising for low cost, roll-to-roll production of organic solar cells, thin-film transistors, sensors and electronics. Examples of preferred materials include organic semiconductors, nanowires (NWs) and composite nanofibers (CNFs). NWs and CNFs have interesting optoelectronic properties including high surface to volume ratio, and tunable conductance and optical absorption. In my group, Flexible Electronics and Energy Lab (FEEL), we have developed methods for synthesis and deposition of NWs and CNFs for flexible and stable organic and inorganic solar cells, sensors and transparent electrodes. Inspired by the fibrous structure of natural systems such as veins of leaf, we have developed methods for controlled deposition of functional CNFs and NW meshes on flexible substrates with improved optoelectronic properties. Different deposition methods such as electrospinning and stamping are used to transfer these functional meshes to flexible substrates. The NW and CNF meshes can be highly conductive and transparent, and thus can be used as a replacement for costly and brittle indium tin oxide (ITO) for solar cells, displays and sensor devices. In addition, novel skin-like strain sensors based on NW and CNF meshes have been developed, which can be used as a synthetic electronic skin for structural health monitoring.

 报告人介绍:
Bio: Dr. Peyman Servati, is an AssociateProfessor with the Department of Electrical and Computer Engineering of the University of British Columbia (UBC), Vancouver, Canada, where he leads Flexible Electronics and Energy Laboratory (FEEL) (http://feel.ece.ubc.ca/) and a is member of Clean Energy Research Centre (CERC).His research interestliesinscalable synthesis and characterization of nanowires and nanostructures, fabrication of flexible and novel electronics and transistors, and development of low-cost photovoltaic devices. Before joining UBC in 2006, he was a research associate at the Centre for Advanced Photonics and Electronics (CAPE) of the University of Cambridge, UK, working on nanowires and printable nanocomposite materials. From 2004 to 2005, he was with Ignis Innovation Inc., a spin-off company of the University of Waterloo, Ontario, Canada, working on thin-film transistor (TFT) backplanes for organic light-emitting diode (OLED) displays.Dr. Servati has eighty papers in peer-reviewed journals and conferences, seven patents, and co-authored three book chapters. His doctoral thesis on mechanically flexible and plastic electronics won the 2005 Doctoral Prize from the Natural Sciences and Engineering Research Council (NSERC) of Canada. He is the winner of 2006 Canada-UK Millennium Research Award and Bronze Medal in the XXV International Physics Olympiad, China, 1994.

 地点:物理楼一楼报告厅
时间:12月12日星期一下午3:30PM

 


seminar(28)
凝聚态物理学术报告会

Title:Charge and Spin Transports at Surfaces of Strong Electron-Phonon / Spin-Orbit-Coupling Material

 Speaker:Shuji HASEGAWA,
Department of Physics, University of Tokyo

 Time: 13:30, Nov. 23 (Wednesday)
Place: Lecture Hall of Dept. of Phys. (The 1st Floor of Physics Building).

 

Transports of charge as well as spin at crystal surfaces are now intensively studied due to interests of fundamental physics as well as possible applications to devices. Surface electronic states are generally decoupled from the bulk states and therefore intrinsically low-dimensional. Furthermore, space-inversion symmetry is broken down at crystal surfaces. These effects provide rich physics of transport, especially on surfaces of strong electron-phonon-coupling (EPC) and spin-orbit-coupling (SOC) materials.
Monolayer of Indium-covered Silicon surface, Si(111)-R7xR3-In surface superstructure, is known to show a large electron-phonon coupling constant [1] and exhibit an energy-gap opening below about 3 K, which is assigned to be a superconducting gap [2]. We have recently confirmed by resistance measurements with ‘sub-Kelvin micro-four-point probe method in UHV’ that this is the first example of ‘monolayer superconductor’. The superconducting transition was very broad due to Kosterlitz-Thouless transition for a 2D system.
The surface-state bands of strong SOC crystals such as Bi and Bi alloys, are known to be spin-split, which is called by Rashba effect [3-6]. Similar effect is observed on a special kind of materials called topological insulators such as BiSb, BiSe, and BiTe alloys. Some of them have spin-split Dirac-cone type surface-state bands. This implies that spin-polarized current will flow at the surfaces of such materials. In my presentation, by using samples of pure Bi [3-6], BiSb [7], BiSe [8,9], and BiTe, I will show that the surface-state bands are really spin-split and the Dirac-cone conductivity is directly measured by microscopic four-point probe method in UHV. An on-going project to detect the spin-polarization of surface current by using magnetic tips in a four-tip STM will be also introduced.

[1] S. Yamazaki, et al., Phys. Rev. Lett. 106, 116802 (2011).
[2] T. Zhang et al., Nature Phys. 6, 104 (2010).
[3] T. Hirahara, et al., Phys. Rev. Lett. 97, 146803 (2006).
[4] T. Hirahara, et al., Phys. Rev. B 76,153305 (2007).
[5] T. Hirahara, et al., Appl. Phys. Lett. 91, 202106 (2007).
[6] T Hirahara, et al., New J. Phys. 10, 083038 (2008).
[7] T .Hirahara, et al., Phys. Rev. B81, 165422 (2010).
[8] Y. Sakamoto, et al., Phys. Rev. B81, 165432 (2010).
[9] T. Hirahara, et al., Phys. Rev. B82, 155309 (2010).

 


seminar(26)
凝聚态物理学术报告会

题目:Spintronics study in III-V semiconductors
 报告人:Prof. Cui Xiaodong
The University of Hong Kong

摘要
In this talk, I report our experimental research on spintronics in
nonmagnetic III-V semiconductors. We observe magneto-electric photocurrent
generated via direct inter-band transitionsin an InGaAs/InAlAs
two-dimensional electron gas by a linearly polarized incident light. The
electric current is proportional to the in-plane magnetic field, which
unbalances the velocities of the photoexcited carriers with opposite spins
and consequently generates the electric current from a hidden spin
photocurrent. The spin photocurrent can be evaluated from the measured
electric current, and the conversion coefficient of spin photocurrent to
electric current is self-consistently estimated to be 10-3~ 10-2 per Tesla.
The observed light polarization dependence of the electric current is well
explained by a theoretical model which reveals the wave vector angle
dependence of the photoexcited carrier density.

时间:2011年6月7号下午15:00
地点:物理楼一楼报告厅

 


seminar(25)
凝聚态物理学术报告会

题目: Crystal growth of cuprate and iron chalcogenide superconductors by travelling floating zone and Bridgman methods

报告人:Kazimierz Conder
Laboratory for Developments and Methods, Paul Scherrer Institute, Switzerland

摘要:A principle and application of Travelling Solvent Floating Zone (TSFZ) method for crystallization of La2-xSrxCuO4 and spin ladder Sr14-xCaxCu24O41 cuprate superconductors will be presented. For the later the mirror furnace was modified to ensure a stable crystal growth at oxygen pressure up to 35bar. Iron-chalcogenide single crystals Fe1+ySexTe1-x and A1-xFe2-ySe2-z (A=K, Rb, Cs) were grown by the Bridgman method. Alkali metal intercalated crystals are showing superconductivity at about 30K and coexistence of magnetism and superconductivity.

时间:2011年6月3日星期五下午3:00
地点:物理楼一楼会议室

 


seminar(24)
凝聚态物理学术报告会

题目:Surface electronic structure of Bi2Se3

地点:物理楼一楼会议室
时间:2011年5月31日下午3:00
报告人:Prof. Philip Hofmann, Department of Physics and Astronomy, Aarhus
University
摘要:

The so-called topological insulators are well-known, off-the-shelf
materials, but they have a previously overlooked and profound "topological"
property which forces their surfaces and edges to be metallic, in contrast
to the insulating bulk. Moreover, the one-dimensional (two-dimensional)
metal at the edge (surface) of a topological insulator was shown to be
inherently robust against disturbances, and to possess special transport
properties linked to the electron's spin, leading to many exciting
predictions for new physics and potential applications.


In this talk, I will also discuss recent results on the electronic structure
and electron dynamics of the prototypical topological insulator Bi2Se3. In
particular, I will focus on the formation of a quantum-confined
two-dimensional electron gas (2DEG) in the conduction band of Bi2Se3 and the
eventual splitting of the 2DEG states by a strong spin-orbit interaction. I
will also discuss the strength of the electron-phonon coupling on Bi2Se3 and
the influence of non-magnetic adsorbates on the surface electronic
structure.

 


seminar(23)
凝聚态物理学术报告会

报告题目: 铁基超导体磁性的来源
报告人:张宇钟 教授  同济大学物理系
摘要:
近年来,铁基高温超导体引起了人们极大的关注。由于其超导相通常出
现在铁磁相附近,确定铁基高温超导体磁性的来源显得尤为重要。这里
我们通过第一性原理计算及动力学平均场计算提出铁砷超导体母态的弱
磁性可能由巡游电子的费米面筑巢效应以及不同阻挫强度的轨道间耦合
效应共同引起的。

 报告人简介:
 1997年上海交大应用物理系学士学位,2002 年获得复旦大学理论
 物理博士学位。博士期间及博士毕业后先后在香港中文大学物理系、
 德国马普所德累斯顿复杂体系研究所(2002-2005)、日本东京大学
 固体物理研究所(2005-2006)、日本东京大学应用物理系(2006-2007)
 以及德国法兰克福歌德大学理论物理研究所(2007-2010)等院校、
 研究机构进行了为期8 年的访问研究工作。于2010 年10 月被聘为同济
 大学物理系特聘教授。已发表SCI 论文30 余篇,其中包括Nature Materials
 1 篇以及Physical Review Letters 5篇。主要从事凝聚态理论方面的研究,
 如铁基超导体的超导与磁性机制的研究、阻挫体系奇异的量子相变
 行为的研究、多轨道体系相图的研究、强关联体系第一性原理的描述、
 新材料的理论设计、低维系统的相变、赝能隙及Mott 相变的研究等等。


时间:2011年5月24日下午3:00
地点:物理楼一楼报告厅

 


seminar(22)
凝聚态物理学术报告会

Impact of metal impurities to the solar cell performance

Prof. Gianluca Coletti

Energy Research Centre of the Netherlands

Abstract

The impact of Fe, Cr, Ni, Ti and Cu is investigated in a model experiment. Impurities have been introduced to high purity feedstock to study their impact on the solar cell performance along the entire value chain. Characterisation on wafer and solar cell levels is presented. A physical model is presented and validated experimentally in order to define the impurity impact and arrive to SoG feedstock specifications.

Gianluca Coletti is senior scientist at ECN solar energy where leads research projects in the area of solar cell technology and Si material and coordinates the PV silicon material area. He has more than 10 years experience in PV with 45 publications in various scientific journals (like Advance Functional Materials, JAP, APL and Progr. in PV) and conferences. Invited speakers at several international PV conferences, he is considered leading expert in the area of silicon materials for PV.

时间:2011年5月9日星期一下午3:00
地点:物理楼一楼报告厅

 


seminar(21)
凝聚态物理学术报告会

题目:Quantum-Interference Transport Properties of Metallic Nanowires
报告人:林志忠教授
台?交通大?物理研究所及?子物理系

摘要:
In this talk, I will discuss three topics concerned with quantum-interference electron transport phenomena in metallic nanowires at liquid-helium temperatures.

(1) I will discuss the weak-localization and weak-antilocalization effects in tin-doped indium oxide (ITO) nanowires. In this class of metallic nanowires, we found that the electron dephasing length is
very long, reaching above 500 nm at 1 K. Furthermore, we found that the spin-orbit coupling in this material can be enhanced by disorder. [Y. W. Hsu et al., Phys. Rev. B 82, 195429 (2010).]

(2) I will discuss our recent observation of time-dependent universal conductance fluctuations (UCF) in metallic ruthenium dioxide (RuO_2) nanowires. The conductance fluctuation amplitudes increase with decreasing temperature. The root-mean-square amplitude reaches a fraction of the quantum conductance (e^2/h) below 1 K. These UCF are shown to originate from the scattering of conduction electrons with
mobile defects (moving scattering centers) which behave like two-level systems. In sharp contrast, inITO nanowires, the defects are “stable” in space, and hence the usual magnetic-field dependent UCF are observed.

(3) If time permits, I will briefly discuss the electronic conduction processes through “nanocontacts” which inevitably form at every interface between a metallic nanowire and a lithographic contacting electrode. We found that, in many cases, the charge conduction
processes can be explained in terms of the theoretical model of fluctuation-induced tunneling conduction across a mesoscopic tunnel junction previously formulated by Ping Sheng. [Y. H. Lin et al., Nanotechnology 19, 365201 (2008).]


时间:2011年4月18日
地点:物理楼一楼报告厅


seminar(20)
凝聚态物理学术报告会

Stripe Domain Phase at the Spin Reorientation Transition of 2D Magnetic System

邱子强
Physics Department, University of California at Berkeley

Electrons in solids determine most of the materials properties. An electron consists of charge and spin. While the electron charge determines the electronic properties, the alignment of electron spins generates magnetism. It is generally believed that a combination of the electron spin and charge freedoms in solids has a potential of creating new generation spintronics technology.

The removal of the spin degeneracy in magnetic materials leads to an inherent spin-charge correlation. Therefore magnetic nanostructures offer a great opportunity for tailoring the spin and charge properties at the nanometer scale. In fact, research on magnetic nanostructures has been developed rapidly in the last two decades with many exciting discoveries such as oscillatory interlayer coupling and giant magneto resistance (GMR).

时间2010年7月2日 星期五下午1:00
地点:物理楼1楼报告厅
 


seminar(19)

凝聚态物理学术报告会
Anisotropic properties of superconducting state in pnictides

Roman Puzniak
Institute of Physics, Polish Academy of Sciences

The recent discovery of superconductivity in iron-pnictides (Y. Kamihara et al., J. Am. Chem. Soc. 130 (2008) 3296) stimulated extensive experimental and theoretical work to explore the fundamental mechanisms of the pairing in these novel high-temperature superconductors. Here, the anisotropic properties of high-quality single crystals of optimally doped SmFeAsO1 xFy, NdFeAsO1 xFy, and Ba1 xRbxFe2As2 were studied by torque and SQUID magnetometry. It was found that in the superconducting state the magnetic penetration depth anisotropy parameter increases with decreasing temperature, in contrast to the steadily decreasing upper critical field anisotropy parameter. Investigations of the field dependence of penetration depth in SmFeAsO1 xFy show a pronounced decrease of the superfluid density as the field is increased. The results are interpreted in terms of a two-gap model and compared to those of various layered high-temperature superconductors such as other iron-based superconductors, MgB2, and cuprates.

时间2010年5月25日 星期二下午3:00
地点:物理楼1楼报告厅


seminar(18)

凝聚态物理学术报告会
Recurrence and Networks

Yong Zou
Potsdam Institute for Climate Impact Research

In this talk, I will report some recent advances in the understanding of recurrence properties, their applications to quantify the dynamics of the underlying systems, and the interrelationship with the research line of complex network. In particular, I show an example of complex network from climate system; reconstruction of complex networks driven by large scale data sets; identification of the correct coupling directions; characterization of structural properties of time series from complex network perspective. It is demonstrated that there are fundamental relationships between many topological properties of the network and different non-trivial statistical properties of the phase space density of the underlying dynamical system. Hence, this novel interpretation of the recurrence yields new quantitative characteristics (such as average path length, clustering coefficient, or centrality measures of the network) related with the dynamical complexity of a time series, most of which are not yet provided by other existing methods of nonlinear time series analysis. Finally, I will propose to use measures of complex networks to identify dynamical transitions including both modeled systems and the real time series. Some particular interesting complex periodic windows are identified by our methods.

时间2010年5月18日 星期二下午3:00
地点:物理楼1楼报告厅


seminar(17)

凝聚态物理学术报告会
胶体物理:最简单的软物质物理

马红孺
上海交通大学物理系

胶体也许是所有软物质系统中最简单的一类,特别是作为模型来研究的硬球胶体,其地位类似于气态物理中的理想气体和固态物理中的简谐固体。与气态物理和固态物理不同的是,这样一个最简单的模型也没有精确求解,因此,只有在计算机高度发展的今天,才能够对于胶体的理论研究作出一些有价值的工作。我们将简单介绍胶体物理的基本出发点,感兴趣的问题和基本研究方法。在此基础上,报道一点我们关于多组元系统的研究工作。


时间2010年5月11日 星期二下午3:00
地点:物理楼1楼报告厅
 


seminar(16)

凝聚态物理学术报告会
Superheating effect of REBCO thin films
and its application to a seed crystal in
melt-textured growth
姚忻
上海交通大学物理系


We report a superheating phenomenon of YBCO thin film by real-time observation of its melting process under a high temperature optical microscope. It was found that the melting occurred at a temperature up to 50 K higher than the peritectic temperature of YBCO (1010C). Further, a systematic investigation was conducted on superheating mechanism of REBCO film and its correlation with film quality. Moreover, using REBCO thin films as cold-seeds, high performance REBCO bulks were successfully grown in the melt-textured process.

 

时间2010年4月27日 星期二下午3:00
地点:物理楼1楼报告厅
 


seminar(15)

凝聚态物理学术报告会
The Dynamics of Membranes
胡丹
上海交通大学自然科学研究院

 

A director model on the dynamics of a lipid or bio- membrane is constructed. In this model, we derive the evolving equations of the surface geometric quantities and the dynamic equations of the membrane, taking into account the effects of elasticity, viscosity, and membrane incompressibility, with and without the presence of bulk fluid. We also consider the effect of local spontaneous curvature which may arise from the presence of membrane proteins. Numerical simulations on the cylindrical and axial-symmetrical membrane and linearization analysis on the planar membrane are carried out based on the director model and its reduced model. The results of the linearization analysis appear to be consistent with the experiments for low wavenumber case and with the MD simulation for the high wavenumber case.


时间2010年4月20日 星期二下午3:00
地点:物理楼1楼报告厅


seminar(14)

凝聚态物理学术报告会

纳米(生物)通道内水分子的动力学研究:
物理、可能生物意义和潜在应用
方海平
中国科学院上海应用物理研究所
纳米管道中水的传输对生物、物理和纳米技术等都非常重要。例如,生物细胞膜上的蛋白水通道(发现者获2003诺贝尔化学奖)是生命的关键,污水处理和海水淡化的关键是管道中水流的传输。生物细胞膜上的蛋白水通道为我们提供了水高速传输并能阻挡离子通过的样板,但是其物理机理还没有完全理解。在这个报告中,我们将介绍这种水通道的特殊物理、可能生物意义和应用前景。这些研究基于纳米碳管的模型系统,和全原子分子动力学模拟。这些内容包括:水分子在透过这种纳米水通道时,表现出与宏观通道完全不一样的力学、电学响应开关特性;参考生物水通道蛋白结构,提出一种由电荷驱动的纳米尺度水泵;利用受限于细纳米管内水分子氢键取向的协同性,提出并数值验证了微弱信号可通过水传递和放大;预言管外电荷可以对纳米管内水和生物分子混合体的操控,提出纳米管中的实验室构想;理论预言常温下不亲水的纳米水层。
相关文章:
1. A charge driven molecular water pump, NATURE Nanotechnology 2, 709-712 (2007)
2. Electrostatic Gating of a Nanometer Water Channel, PNAS 104, 3687 (2007)
3. Water-mediated signal transduction with Y-shaped carbon nanotube, PNAS, 106, 18120 (2009)
4. Enhancement of Water Permeation across a Nanochannel by the Structure outside the Channel, PRL. 101, 257801 (2008).
5. Stable Liquid Water Droplet on a Water Monolayer Formed at Room Temperature on Ionic Model Substrates, PRL 103,137801 (2009).
6. Manipulating Biomolecules with Aqueous Liquids Confined within Single-walled Nanotubes, JACS 131, 2840 (2009)
7. Controllable water channel gating of nanometer dimensions, JACS 127, 7166 (2005)

时间2010年4月13日 星期二下午3:00
地点:物理楼1楼报告厅


seminar(13)

凝聚态物理学术报告会

软物质中的临界现象及相变行为
Prof. Limei Xu
WPI Advanced Institute for Material Research
Tohoku University
Abstract
The phase behavior of substances is important for the understanding of the basic questions in supercooled liquids and material science. In this talk, I will present some of our studies on the critical phenomenon (polymorphism in liquid) associated with the anomalous behavior in water-like systems, as well as glass transformations (polyamorphism in glass) observed in bulk metallic systems. Our results based on the studies of the thermodynamic, dynamic, and structural properties of the model system are consistent with the experimental observations in water and provide a possible way for experiment to locate the liquid-liquid critical point buried in deep supercooled region.
References
[1] O. Mishima and H. E. Stanley, Nature 396, 329-335 (1998)
[2] L. Xu et al., Proc. Natl. Acad. Sci. 102, 16558-16562 (2005).
[3] L. Xu et. al, Nature Physics 5, 565-569 (2009).

时间:2010年4月7日 星期三 下午1:00
地点:物理楼1楼报告厅


 seminar(12)

报告题目:Interband Cascade Lasers: from concept to devices and applications

报告人:杨瑞青 教授
University of Oklahoma
时间:2010年1月4日星期一下午3:00
地点:物理楼一楼会议厅

摘要:Interband cascade (IC) lasers take advantage of the broken band-gap alignment in type-II quantum wells to reuse injected electrons in cascade stages for photon generation with high quantum efficiency and represent a relatively new class of mid-infrared light sources. Unlike intraband quantum cascade lasers, IC lasers use interband transitions for photon emission without involving fast phonon scattering, making it possible to significantly lower the threshold current density. IC lasers are designed entirely based on quantum mechanics and grown by advanced technology such as molecular beam epitaxy (MBE). IC lasers offer a wide wavelength tailoring range without being limited by the conduction-band offset in the wavelength region of 3-4 micron where there are hydrocarbon signatures important for life detection in space exploration. Since the proposal of IC lasers in 1994 and the first demonstration in 1997, significant progress has been achieved toward high-performance mid-IR laser devices. Some outstanding performance features such as low threshold current densities (e.g. <2 A/cm2 at 80 K, <400A/cm2 at 300K) and high cw wall-plug efficiency (e.g. >31% at 80 K) partially verified the advantages of IC lasers. Single-mode distributed feedback (DFB) IC lasers have been demonstrated in cw operation for the wavelength range from ~3.2 to 3.6 μm. These DFB IC lasers have been employed for the detection of gases such as methane (CH4), Ethane (C2H6), hydrogen chloride (HCl), and formaldehyde (H2CO), and have been flown on aircraft and high-altitude balloon instruments and measured atmospheric CH4 and HCl profiles. Also, single-mode cw DFB IC lasers have been integrated with TE coolers in a compact butterfly-like package operating at room temperature, which have been delivered for NASA flight mission to Mars. In 2008, cw operation of IC lasers was demonstrated above room temperature (up to 319K) near 3.7 m with low power consumption (<0.6 W at 300K), exceeding the important milestone of IC laser development, namely room temperature cw operation. Recently, we have extended the efficient IC lasers into the longer wavelength region (>7 m) based on plasmon waveguides. In this talk, the development of mid-infrared IC lasers from concept to devices and applications will be reviewed. Their current status and future prospects will be discussed. If time permits, our recent results of photodetectors using IC structures will be presented.


 seminar(11)

报告题目:超快X光成像及其应用

报告人:王宇杰
上海交通大学物理系
时间:2009年12月28日星期一下午3:00
地点:物理楼一楼会议厅

摘要:超快同步辐射X光成像技术是第三代同步辐射光源新发展的成像技术,具有微米空间分辨率和微妙时间分辨率。 该技术在流体力学,材料力学,汽车技术,化工,生物,基础物理各学科都可以找到广泛的应用。报告主要介绍超快成像技术在基础流体力学,软物资结构,汽车内燃机喷雾过程,材料的破碎过程,微流体,小动物的生理动态过程,粒态物理等的一些应用。


seminar(10)

报告题目:氢能源材料和热电材料的第一性原理的模拟研究

报告人:柯学志 教授
华东师范大学物理系
时间:2009年12月21日星期一下午3:00
地点:物理楼一楼会议厅

摘要:众所周知,能源和环境已成为全人类尤其关注的两大问题。按现在的开采量计,石油还可用50年左右,天然气为60年左右,煤则为200年左右。面对日趋严重的能源和环境问题,如何在开发和使用新资源的同时又保护好我们赖以生存的环境,已经成为一个全球性的重要课题。因此,对能源材料进行基础研究将是十分有意义的。我们的报告将会涉及氢能材料和热电材料。氢能材料方面我们将会讨论:氢气的产生提纯,氢气的储存,和固体氢燃料电池的隔膜。热电材料方面我们将会讨论纳米颗粒在体块材料中的生长机制。所涉及的材料将有PdAg, LiAlH4, CsHSO4, PbTe-AgSbTe2等。研究的性质有:零点能,原子扩散(用NEB方法),晶格动力学,Gibbs自由能,P-T相图等


seminar(9)

报告题目:Quantum memory: Coherent control of an electron spin decoherence in semiconductor quantum dots

报告人:张文献 教授
复旦大学光科学和工程系
时间:2009年12月14日星期一下午3:00
地点:物理楼一楼会议厅

摘要:Quantum memory is a core component of a quantum computer where quantum mechanics, instead classical mechanics, becomes dominant if the device size approaches nanometer scale. Because of it potential scalability and its long relaxation time T1, an electron spin in a semiconductor quantum dot is one of the most promising candidate for a solid-state-based quantum computer architecture. Decoherence of the electron spin in quantum dots, through hyperfine coupling to its surrounding nuclear spins, is the major obstacle for the realization of a quantum memory. Typical decoherence time T2* is 10 ns for GaAs quantum dots at low temperature (~100 mK) and in sub-Tesla magnetic field. I address the decoherence mechanism and the decoherence process of an electron spin in quantum dots, as well as quantum control of the decoherence to extend the coherence time 1000 times longer via dynamical decoupling method by subjecting the electron spin to a sequence of control pulses. Experimental related considerations, such as external magnetic field, initial bath polarization, and control pulse imperfection, are also discussed.


seminar(8)

报告题目:Application of Nanotechnology in Silicon Solar Cells

报告人:沈文忠 教授

上海交通大学物理系

时间:2009年12月7日星期一下午3:00
地点:物理楼一楼会议厅

摘要:Both the crystalline Si and the second-generation Si thin film solar cells dominate the current photovoltaic (PV) industry. Third-generation nanotechnology approaches aim to decrease costs to well below the $1.0/W level of second-generation PVs to $0.5/W, potentially to $0.2/W or better, by significantly increasing efficiencies but maintaining the economic and environmental cost advantages of thin-film deposition techniques. This one-hour talk will present the recent achievements in Si nanocrystalline and nanowire solar cells, since the future PV industry may belong to these nanostructured Si solar cells.Hydrogenated nanocrystalline silicon (nc-Si:H) is a mixed material comprised of an amorphous phase and crystalline grains with a wide range of crystalline volume fraction. Compared with the bulk silicon, strong optical absorption and high photocurrent are found in nc-Si:H thin films and attributed to the enhancement of the optical absorption cross section and good carrier conductivity in the nanometer grains. In comparison with the amorphous silicon thin film solar cells, there is very weak light- and current-induced degradation caused by the Staebler-Wronski effect in nc-Si:H thin film solar cells. Small grains and intermediate range order may provide a better grain boundary passivation and also improve the cell stability.We will present two schemes of three kinds of novel nc-Si:H thin film solar cells on the basis of the fact that the prevention of hot carrier cooling via phonon emission may ultimately yield meaningful efficiency gains for solar photon conversion: (1) Tandem scheme for triple-junction nc-Si:H solar cells (band gap is tuned by the dot size) with poly-Si (1.1eV) thin films, which can be maturely grown on glass substrates. (2) Hot carrier scheme utilizing the hot carriers before they relax to the band edge via phonon emission: (i) Hot carrier transport through minibands. The observed minibands in nc-Si:H thin films could be expected to slow the carrier cooling and permit the transport and collection of hot carriers at the respective p and n contacts to produce a higher photopotential. (ii) Multiple exciton generation (MEG). Highly efficient MEG effect in colloidal Si nanocrystals has been reported at lower photon energies in the visible region, which opens the possibility to expand to nc-Si:H films for MEG cells with increasing power conversion efficiency.On the other hand, nanowires can be used as efficient electrical pathways of the generated charge carriers due to high electrical mobility, especially at longer wavelengths. Nanowires can also increase the likelihood that all photogenerated electrons have a direct connection to the collection electrode. Recent theoretical and experimental work has demonstrated that the reflectance of nanowires is significantly lower than the film in the entire spectral range due to the reduced density, which can be achieved without specially designed antireflection coatings. The talk will also present (1) the preliminary application of Si nanowire arrays in planar Si solar cells, (2) the radial Si nanowire solar cell concept for use of inexpensive candidate materials (e.g., poly-Si and UMG-Si) in PV applications, and (3) recent achievements of single nanowire Si solar cells.


seminar(7)

报告题目:Vertical Silicon Nanowires: Potential Enablers for Solar Cells and Electron Emitters

报告人:王业伍教授

浙江大学

时间:2009年11月30日星期一下午3:00
地点:物理楼一楼会议厅

摘要:由于硅线在太阳能电池和场发射器件方面有着巨大的应用前景,硅线的相关研究引起了人们极大地重视。本报告将主要介绍硅线的可控生长及相关物性研究,我们采用金属催化方法,在超高真空化学气相沉积系统中,以硅片为衬底生长高度有序且形貌可控的硅纳米线阵列;观察金属催化硅线的氧化行为;测试分析硅线的电学特性,揭示金属催化剂在硅线生长过程中的行为;最后提出新型太阳能电池结构模型。 


seminar(6)

报告题目:Water transportation across narrow channel on nanometer dimension

报告人:万荣正研究员
中国科学院上海应用物理研究所
时间:2009年11月23日星期一下午3:00
地点:物理楼一楼会议厅

摘要:

Since the discovery of the carbon nanotube and Aquaporin, the study of the transportation of water across nanochannels becomes one of the hot subjects. When the radius of a nanochannel is only about one nanometer or a little larger, water confined in those nanoscale channels usually exhibits dynamics different from those in bulk system, such as the wet-dry transition due to the confinement, concerted hydrogen-bond orientations and flipping, concerted motion of water molecules, and strong interactions with external charges. Those dynamics correlates with the unique behavior of the water transportation across the channels, such as the extra-high permeability, excellent on-off gating behavior with response to the external mechanical and electrical signals and noises, enhancement by structure outside the channel, directional transportation driven by charges close to a channel or electric field. In this article, we review some of the recent progress on the study of the water molecules inside those narrow nanochannels.

                                                                                                              

seminar(5)

报告题目:纳米机械振动诱导的量子光学和非线性光学效应
报告人:“朱卡的

时间:2009年11月9日礼拜一下午3:00
地点:物理楼一楼会议厅

摘要:近年来,纳米机械系统在物理、电子、工程、生物、化学和医学等科学和技术领域引起了人们的广泛关注。这些纳米机械系统由于具有超高的品质因子、超高振动频率,超轻的质量等优良可调性能, 因此,这样的系统可应用于超高灵敏度的测量和精确的量子测量,比如集成化的纳米机械系统能够对极小的质量和极弱的力进行精确测量。另一方面,如果该纳米机械系统与其它小量子系统(如原子、电子、量子点、单电子晶体管等) 耦合起来,则该耦合系统还可用于研究许多奇异的量子现象和检测基本的量子定律。比如通常人们认为量子定律只能在微观系统中观测到,在宏观系统中是难以观测到典型的量子效应如薛定谔猫态,量子纠缠态等,但利用纳米机械振子耦合系统却有可能实现这些宏观量子效应。再如,利用该纳米机械耦合系统还可以将纳米振子冷却至极低温度甚至到基态。另外,把这种纳米机械耦合系统用于量子信息处理和量子计算也是一个可能的应用。可以断言,随着纳米机械系统器件的广泛应用,这将成为量子力学全面渗入工程学的一个重要标志。最近,我们研究了纳米机械振子-量子点耦合系统的相干线性与非线性光学性质。我们的研究结果表明:机械振动可以诱导出类似于相干布居数振荡(CPO)的效应,我们称之为“机械振动诱导布居数振荡”(Mechanically Induced Coherent Population Oscillation)(简称MICPO), 由于该系统纳米机械振子的相干振动寿命特别长(约微秒量级),既使系统耦合很弱,该效应也特别明显,可用于精确测量纳米机械振子的振动频率和耦合强度以及设计新型全光开关等。类比于三能级系统的电磁诱导透明(EIT)效应和两能级系统的相干布居数振荡(CPO),我们预言该耦合系统可以有类似的超慢(快)光效应、光存储效应以及其它奇异的量子光学和非线性光学效应。


 seminar(4)

报告题目:基于高场阳极氧化铝膜的高性能湿敏传感器
报告人:姚陆军(上海交通大学)
摘要:人类的生存和社会活动与湿度密切相关。随着现代化的实现,很难找出一个与湿度无关的领域来。由于应用领域不同,对湿度传感器的技术要求也不同。从制造角度看,同是湿度传感器,材料、结构不同,工艺不同,其性能和技术指标有很大差异。湿敏传感器主要分为电阻式和电容式两大类,阳极多孔氧化铝对湿敏的敏感性研究已早在1953年被提出,但传统的多孔氧化铝薄膜对湿度的灵敏性有一定的缺陷,本报告着重提出了一种基于高场的阳极氧化的多孔氧化铝膜的湿敏传感器的制备及性能研究,并发现其湿敏元件在低湿区的灵敏性,特定区域的灵敏度得到大大的提高以及响应与回复时间的大大缩短,这为获得高性能氧化铝湿敏传感器提供了一种有效的方法。

 

报告题目:Growth of high performance SmBCO bulk superconductor with the addition of Sm2Ba4Cu2O9 phase
报告人:孙立杰(上海交通大学)
摘要:自从RE-Ba-Cu-O高温超导材料被报导发现以来,很多研究者为了能实现其实际应用领域而开展了大量的工作来提高超导体的性能。其中,大尺寸取向生长,内部结构,元素替代(例如:用轻稀土代替钇)是目前研究的几个主要方向。在本工作中,我们首先在Sm-Ba-Cu-O系统中观察到了Sm2Ba1Cu1O5 (Sm211)相和一种新发现的Sm2Ba4Cu2O9 (Sm242)相之间存在着外延关系。通过在块材生长中引进这类Sm242相,希望能够对超导性能有所改善。利用SmBCO和NdBCO薄膜籽晶,我们成功的在空气中用熔融织构方法生长出了SmBa2Cu3O7(Sm123 或SmBCO)块体材料。通过研究,我们发现随着Sm242相添加量的增加,块材中Sm211颗粒的尺寸和分布获得了相当的改善。通过优化Sm242相的添加量,获得的Sm123块材具有 94K的高临界温度(Tc) 和小于1K的临界转变宽度(ΔTc),这是目前在空气中生长同类样品所获得的最好结果。 在测量样品的临界电流密度(Jc) 时,我们在中高场下观察到了一个相对较强的第二峰,根据分析,这个第二峰的出现是由于Sm123内形成的组分涨落形成的。为了进一步提高Jc值,还需要对内部钉扎中心的数量和分布进行进一步改进."

时间:2009年11月2日星期一下午3:00
地点:物理楼一楼报告厅


 seminar(3)

报告题目:Spin-dependent electron transport in noncollinear magnetic multilayers
报告人:张建卫教授 同济大学
时间:2009年10月26日星期一下午3:00
地点:物理楼一楼报告厅
摘要:We studied spin-dependent electron transport in noncollinear magnetic multilayers Co/Cu/Co by using the Boltzmann equation in the layer-by-layer approach. Without a priori set the transverse part of the spinor distributions to zero in the ferromagnetic layers and by adopting new mechanism for the “injection” of these components in the magnetic layers, we have been able to achieve a steady state for the spin current across the noncollinear multilayer in which the spin current continuously changes its direction over a distance given by a new transport length scale, which is about 3nm for a typical ferromagnetic 3d transition-metal such as Co. This has a direct impact on the thickness dependence of the spin torque in a thin magnetic layer. Furthermore, our theory always obtain a lower resistance of noncollinear magnetic multilayer and a enhanced spin torque about 50% greater for the same amount of electrical energy at particular angle. Finally, we have used the time dependent spin diffusion equation, to study the time evolution of spin torque, and find it achieves its steady state in about 75 femtoseconds after undergoing damped oscillation with a period of about 5 femtosecond.


 seminar(2)

报告题目:Electromagnetic metamaterials

报告人: Prof. Siu Tat Chui (徐少达 教授) University of Delaware

时间:2009年10月19日星期一下午3:00
地点:物理楼一楼大会议室

摘要:We describe two of our recent results in this direction.
(1) ``Rectifying" reflection from a magnetic photonic crystal:
Photonic analog of the Quantized Hall effect?
When an oscillating line source is placed in front of a special mirror consisting of an array of flat uniformly spaced ferrite rods, half of the image disappeared at some frequency. We believe that this comes from the coupling to photonic states of the magnetic surface plasmon band. These states exhibit giant circulations that only go in one direction due to time reversal symmetry breaking. Possible applications of this ``rectifying" reflection include a robust one-way waveguide, a beam bender and a beam splitter, which are shown to work even in the deep subwavelength scale.

(2) Kirchoff's law at finite frequencies?
To generalize Kirchoff's circuit equations for a general wire network, we find that it is necessary to introduce localized electric fields at ends and junctions of the network. With this the resonance of the recently popular split r



上海交通大学人工结构及量子调控教育部重点实验室

联系地址:上海闵行区东川路800号物理楼130室 管理员信箱:ximei_zhao@sjtu.edu.cn