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Seminars 2013
| Title: | Microwave Metamaterials and Applications |
| Speaker: | Professor Tie Jun Cui |
| Date: | 18 December 2013 |
| Time: | 11am - 12pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Assistant Professor Zhang Baile |
| Abstract: | In this seminar, I will present the recent advances on microwave metamaterials conducted at Southeast University
in China in three perspectives: the microwave metamaterial lenses, transformation electrostatics, and plasmonic
metamaterials.
In the first part, I will introduces several types of microwave lenses which are composed of homogeneous or inhomogeneous metamaterials based on different physics principles, including super-resolution imaging lenses, polarization convention lenses, and high-gain lens antennas.Transformation electrostatics is a d.c. reduction of the transformation optics. In the second part, I will introduce a series of transformation electrostatics devices. Finally, I introduce a kind of planar plasmonic metamaterial on thin metal films with nearly zero thickness. Such a planar plasmonic metamaterial can sustain highly localized SPPs along two orthogonal directions in the terahertz and microwave regions in broadband by keeping good modal shape and propagating long distance with low bending loss. Based on the above idea, we also present the concept of conformal surface plasmons (CSPs), i.e., the surface plasmon waves that can propagate on ultrathin and flexible films to long distances. |
| Title: | The International Physics Course (IPC) in Osaka University, Japan |
| Speaker: | Professor H. Takabe |
| Date: | 4 December 2013 |
| Time: | 2pm - 5pm |
| Venue: | MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | Assistant Professor Cheong Siew Ann |
| Abstract: | I am the chairman of IPC, International Physics Course (IPC), Osaka University, Japan (http://www.rcnp.osaka-u.ac.jp/~ipc/). I will introduce the IPC and call for application to study in Osaka University. The IPC was established 2009 to make Osaka University more attractive for foreign students so that no language barrier for anyone who can use English. In addition, I will give a short lecture on the hot topics of my research on the vacuum breakdown with ultra-intense lasers. NTU graduate Mr. Teo has joined from October 1st and his video message will be shown. After a break, you will have time to ask any questions on IPC application process, study and research at Osaka University, and stay in Japan etc, any kind of questions. |
| Title: | Quantum optics with semiconductors: polariton quantum fluids and single photons sources |
| Speaker: | Dr Alberto Bramati |
| Date: | 20 November 2013 |
| Time: | 11am - 12.30pm |
| Venue: | SPMS MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | |
| Abstract: | Polaritons, half-light half-matter mixed states arising from the strong coupling between excitons and photons in
semiconductor microcavities, are composite bi-dimensional interacting bosons. They can manifest macroscopic
quantum coherence effects at high temperatures (5-300 K) due to their very low mass. In particular, polaritons
behave like a quantum fluid with specific properties coming from its intrinsic out of equilibrium nature,
determined by the short polariton lifetime (some picoseconds).
In the first part of the talk, I will briefly review the superfluid and Cerenkov regimes [1] in these systems, then I
will discuss the formation of quantized vortex and dark solitons in a polariton quantum fluid interacting with a
large obstacle [2, 3]. Finally, the possibility to generate vortexantivortex lattices in a confined geometry will be
discussed.
These results demonstrate that the polaritons are an ideal system for the study of the quantum fluid properties.
In the second part of the talk I will present our recent results on efficient room temperature single photon
emitters based on core/shell colloidal semiconductor nanocrystals.
In such structures, the competition between radiative and non-radiative recombination channels induces
photoluminescence fluctuations between on and off states known as blinking. The shell engineering is a suitable
strategy to control recombination paths and has been used to produce almost non-blinking nanocrystals [4],
although accompanied by undesired increasing of multi-excitonic emission probability [5].
By using asymmetric core/shell nanoparticles (dots-in rods) with a spherical CdSe core surrounded by a rod-like
CdS shell, blinking effects, multi-excitonic emission and polarization of the emitted photons can be separately
controlled by tuning the shell dimensions [6, 7]. This allows an unprecedented capability in radiative channels
engineering, making dot-in-rods very efficient blinkingfree sources of polarized single photons on-demand.
[1] A. Amo, J. Lefrère, S. Pigeon, C. Adrados, et al., Nature Phys. 5, 805 (2009). [2] A. Amo, S. Pigeon, D. Sanvitto, V.G. Sala, R. Hivet, et al., Science, 332, 1167 (2011). [3] D. Sanvitto, S. Pigeon, A. Amo, D. Ballarini, et al, Nature Photonics, 5, 610 (2011) [4] B. Mahler, P. Spinicelli, S. Buil, X. Quélin, J. P. Hermier, B. Dubertret, Nature materials 2008, 7, 659. [5] Y. S. Park, A. Malko, J. Vela, Y. Chen, Y. Ghosh, F. García-Santamaría, J. Hollingsworth, V. Klimov, H. Htoon, Physical Review Letters 2011, 106, 187401. [6] F. Pisanello, L. Martiradonna, G. Leménager et al., Appl.Phys.Lett. 96, 033101 (2010) [7] F. Pisanello, G. Leménager, L. Martiradonna et al, Adv. Mat. 25, 1974 (2013) |
| Title: | Controlling Leakage Currents in Molecular Electronic Devices |
| Speaker: | Dr Christian A. Nijhuis |
| Date: | 15 November 2013 |
| Time: | 3pm - 4.30pm |
| Venue: | SPMS MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | |
| Abstract: | One of the major goals of molecular electronics is to relate the performance and electronic function of these
devices to the chemical structure and intermolecular interactions of the organic molecules inside them.
Molecular electronic devices are complex physical-organic systems that consist of at least two electrodes, the
organic component, and two (different) organic/inorganic interfaces. Singling out the contribution of each of
these components to the device performance is not straightforward. So far, strong π-π interactions have mainly
been considered for the rational design and optimization of the performances of organic electronic devices,
whereas weaker intermolecular interactions have been largely ignored.1 Here we experimentally show that
subtle changes in the intermolecular van der Waals interactions in the active component of a molecular diode
dramatically impact the performance of the device (See Figure).2 In particular, we observe an odd-even effect as
the number of -CH2- units are varied in a ferrocene-alkanethiolate SAM: as a result of a more favourable van
der Waals interaction, junctions made from an odd number of alkyl units have a lower packing energy by
approximately 0.4-0.6 kcal mol-1 and rectify currents 10 times more efficiently, give 10% higher yield of
working devices and can be made 2-3 times more reproducibly than junctions made from an even number of
alkyl units. Besides subtle changes in the packing energy, we also showed that preparation of the bottomelectrode (especially grain boundaries), the type of the anchoring group, and the purity of the SAM precursor
are crucial. Once the supramolecular structure can be controlled, the electronic structure can also be controlled
which we used to turn around a diode a the molecular level. |
| Title: | Anderson localization of classical waves |
| Speaker: | Dr Sergey Skipetrov |
| Date: | 7 November 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor David Wilkowski |
| Abstract: | Anderson localization is responsible for the metal-insulator transition that can be observed upon increasing impurity
concentration in an otherwise good metal at low temperatures. Starting from a certain critical concentration of
impurities, strong scattering of conduction-band electrons from impurities blocks transport completely. A similar
phenomenon can be observed with classical waves such as light, sound or elastic waves. Scattering from random
inhomogeneities of the medium where they propagate can completely block their transmission through a layer of
disordered material. Classical waves offer an opportunity to observe Anderson localization without additional
complications typical for electronic transport experiments (such as electron-electron and electron-phonon interactions,
need for low temperatures and small samples). They also open new possibilities to design position- and time-resolved
experiments that would exhibit Anderson localization in the most obvious way. However, they also bring in additional
complications that are not present for electronic systems: a part of wave energy is always absorbed and many of
classical waves are vector waves. I will discuss recent theoretical and experimental progress in this exciting field of
research and point out some of the existing controversies and open questions.
References: 1. S.E. Skipetrov and B.A. van Tiggelen Dynamics of Anderson localization in open 3D media Phys. Rev. Lett. 96, 043902 (2006) 2. H. Hu, A. Strybulevych, J.H. Page, S.E. Skipetrov, and B.A. van Tiggelen Localization of ultrasound in a three-dimensional elastic network Nature Physics 4, 945 (2008) 3. N. Cherroret, S.E. Skipetrov, and B.A. van Tiggelen Transverse confinement of waves in three-dimensional random media Phys. Rev. E 82, 056603 (2010) 4. S.E. Skipetrov and I.M. Sokolov Absence of Anderson localization of light in a random ensemble of point scatterers arXiv:1303.4655 5. A. Aubry, L.A. Cobus, S.E. Skipetrov, B.A. van Tiggelen, A. Derode, J.H. Page Recurrent scattering and memory effect at the Anderson localization transition arXiv:1306.2762 6. W.K. Hildebrand, A. Strybulevych, S.E. Skipetrov, B.A. van Tiggelen, and J.H. Page Observation of infinite-range intensity correlations near the 3D Anderson localization transition arXiv:1303.7042 |
| Title: | Lithium Ion Batteries – Materials Aspects and Perspectives |
| Speaker: | Professor B.V.R. Chowdari |
| Date: | 31 October 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Pinaki Sengupta |
| Abstract: | Lithium ion batteries are found to have wide range of applications in variety of mobile devices ranging from simple toys to electric vehicles. The performance of these batteries depends on the choice of constituent materials. In this lecture, the materials aspects and perspectives of these batteries will be discussed. The state-of-art of both electrode and electrolyte materials and results from the wide range of studies made in authors’ laboratory on anode materials will be presented. Optimization of the oxide materials prepared and characterized by variety of techniques and reaction Mechanisms will be highlighted. |
| Title: | Time-Reversal, Waves and Innovation |
| Speaker: | Professor Mathias Fink |
| Date: | 29 October 2013 |
| Time: | 4pm - 5pm |
| Venue: | MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | Associate Professor Claus Dieter Ohl |
| Abstract: | Time-reversal invariance is a very fundamental concept in classical and quantum physics. The objective of this talk is to show how this concept can be turned into a huge source of innovations and successful start-up companies. It was first in the field of acoustics and later for microwaves, where antenna array technology was available, that “time-reversal mirrors” have been built. Such mirrors allow to refocuses in space and time an incident wave field at the original source location regardless of the complexity of the propagation medium. Contrary to intuition, a remarkable property was shown: the more complex the propagation medium, the sharper the focus. Such results have been recently extended to focus on spots much smaller than the wavelength using new sub-wavelength structured media, opening new avenues toward super-resolution imaging and high rate telecommunications. Time reversal mirrors are not only unique research tools in the field of fundamentals physics but they have plenty applications including therapy, medical imaging, telecommunications, underwater acoustics, seismology, human-machine interface. Recently, new tools available in optics such as sensitive and fast megapixel digital sensors and modulators, are opening new perspectives toward time reversal of light.
|
| Title: | Theory of Extremely Correlated Fermi Liquids |
| Speaker: | Professor Sriram Shastry |
| Date: | 18 October 2013 |
| Time: | 11am - 12pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Pinaki Sengupta |
| Abstract: | A novel method for solving the important problem of the tJ model in any dimension is developed, and some applications to the ARPES (angle resolved photoemission) spectra are provided. The important role of dynamical asymmetry between particles and holes is emphasized. |
| Title: | Ultrafast plasmon dynamics of heavily-doped semiconductor nanocrystals |
| Speaker: | Professor Francesco Scotognella |
| Date: | 9 September 2013 |
| Time: | 2pm - 3pm |
| Venue: | EEE Executive Seminar Room (S2.2-B2-53) |
| Host: | Assistant Professor Cesare Soci |
| Abstract: | Ultrafast electron-phonon coupling dominates the optical response of metallic nanostructures
after intense excitation with femtosecond-laser pulses, offering the possibility to achieve optical
modulation with unprecedented terahertz bandwidth [1]. In recent years, efforts have been made
to synthesize heavily doped semiconductor nanocrystals that display plasmonic behaviour with
spectrally tunable features [2]. A discussion on structural aspects, photo-physical properties, and
theoretical and experimental analysis of the linear plasmonic response of colloidal nanocrystals
will be illustrated. Colloidal Cu2-xSe nanocrystals studied by ultrafast (~200 fs) pump–probe
experiments in the near-infrared revealed the existence of strong nonlinearities in the plasmonic
absorption. This is due to the lower carrier density of Cu2–xSe compared to noble metals, which
leads to ultrafast control of the probe signal with modulation depth exceeding 40% in
transmission. A quantitative interpretation of these results based on a two-temperature model will
be presented [3].
[1] Maier, S A “Plasmonics: Fundamentals and Applications”; Springer: New York, 2007; MacDonald K F et al, 2009 Nat. Photonics 3 55–58. [2] Zhao Y X et al, J. Am. Chem. Soc. 131 4253–4261; Luther J M et al, 2011 Nat. Mater. 10 361–366. [3] Sun C K et al, 1994 Phys. Rev. B 50 15337–15348; Scotognella F et al, 2011 Nano Lett. 11, 4711-4717; Scotognella F et al, 2013 EPJB 86, 154. |
| Title: | Magneto-optical Analysis of Magnetic Microstructures |
| Speaker: | Professor Rudolf Schäfer |
| Date: | 6 September 2013 |
| Time: | 9.45am - 11am |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Lew Wen Siang |
| Abstract: | The rich world of magnetic microstructure or magnetic domains, extending from visible dimensions down to the
nano-scale, forms the mesoscopic link between the fundamental physical properties of a magnetic material and its
macroscopic properties and technical applications, which range from films for computer storage technology to
magnetic cores for electrical machinery. Hysteresis phenomena, energy loss in inductive devices, noise in sensors,
or the magnetoresistive properties of modern spintronic devices can be decisively determined by the peculiarities of
the underlying magnetic microstructure, especially by irreversibilities in the magnetization process. Therefore any
development and optimization of magnetic materials, which is usually accompanied by the measurement of
magnetization curves, requires an understanding of the underlying domains and their reaction to magnetic fields,
which, in most cases, can only be gained by direct imaging.
In my presentation I will give a review of magnetic domains, supported by domain observation using Kerr microscopy. After a brief introduction to magnetic energies, I will demonstrate using various examples how these energies act together in the formation of domain patterns. The examples include magnetic films as well as bulk magnetic materials with different strength and symmetry of magnetic anisotropy. It will be shown how domains adapt to increasing specimen thickness (domain branching) and decreasing grain size (nanocrystalline materials and films). Most challenging is the analysis of hidden (internal) domains and processes in bulk material. They are relevant for material performance and their analysis requires surface imaging in combination with domain modeling and some volume-sensitive imaging method. Aside from their scientific and technical relevance, magnetic microstructures are also aesthetically appealing, an aspect that will be part of the presentation. |
| Title: | Revisiting old questions in new materials |
| Speaker: | Dr Shaffique Adam |
| Date: | 5 September 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Pinaki Sengupta |
| Abstract: | From the hard-drives that harness giant magneto-resistance to the transistors that drive modern processors, solid state
physics is at the very heart of the technological revolution. Implied in this effort is a thorough understanding of electronic
systems in nanoscale geometries. In this context, the complex interplay between disorder, electron-electron interactions
and quantum interference is an interesting backdrop to many of the unsolved mysteries in condensed matter
physics. About seven years ago, a new electronic material appeared – notable not only for its ease of preparation and
theoretical simplicity, but also by its promise for future electronic devices [1]. Single monatomic sheets of carbon, known
as graphene, have an electronic dispersion that is reminiscent of light, in that they can be described as a massless Dirac
particle. In many ways, graphene is a textbook system to test physical models – for instance, similar to field-effect
transistors, the electron density in graphene sheets can be modulated by a backgate. However, unlike conventional
semiconductors, the carrier density can be continuously tuned from electron-like carriers for large positive gate bias to
hole-like carriers for negative bias, with the Dirac point defined as the singularity that marks the transition from electrons to
holes. When graphene is close to charge neutrality, its energy landscape becomes highly inhomogeneous, forming a sea of
electron-like and hole-like puddles, which determine the properties of graphene at low carrier density. In this talk. I will
discuss how the electronic properties of the Dirac point provide an intriguing example of how the competing effects of
disorder, electron-electron interactions, and quantum interference conspire together to give a surprisingly robust state
whose properties can be described using semi-classical methods. Armed with this success, I will discuss how future
graphene experiments could shed light on some long-standing open questions in condensed matter physics. References [1] S. Das Sarma, S. Adam, E. H. Hwang, E. Rossi, “Electronic transport in two dimensional graphene”, Rev. Mod. Phys. 83, 407 (2011). |
| Title: | Publishing in Wiley Materials Science Journals |
| Speaker: | Dr Jose Oliveira |
| Date: | 24 July 2013 |
| Time: | 3pm - 4pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Fan Hongjin |
| Abstract: | A highly competitive research environment with increasingly limited research funding has created a "Publish or Perish" attitude among scientists who are judged on the quantity rather than quality of their research articles. This presentation provides a brief overview of current trends and challenges in scientific publishing, some ethical considerations, how publishers and authors interact and influence each other, and how the publishing arena is being transformed. Tips will be presented on how to select an appropriate journal for your paper, what aspects of preparation and presentation to focus on from an editor's and referee's perspective, and hints for increasing the discoverability of your paper after publication. |
| Title: | Nanophotonics Technology and Applications |
| Speaker: | Professor Shaya Fainman |
| Date: | 9 July 2013 |
| Time: | 10.30am - 11.30am |
| Venue: | MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | Assistant Professor Cesare Soci |
| Abstract: | Various future system applications that involve photonic technology rely on our ability to integrate it on a chip to augment and/or interact with other signals (e.g., electrical, chemical, biomedical, etc.). For example, future computing and communication systems will need integration of photonic circuits with electronics and thus require miniaturization of photonic materials, devices and subsystems. Another example, involves integration of microfluidics with nanophotonics, where former is used for particle manipulation, preparation and delivery, and the latter in a large size array form parallel detection of numerous biomedical reactions useful for healthcare applications. To advance the nanophotonics technology we established design, fabrication and testing tools. The design tools need to incorporate not only the electromagnetic equations, but also the material and quantum physics equations to include near field interactions. These designs are integrated with device fabrication and characterization to validate the device concepts and optimize their performance. Our research work emphasizes the construction of passive (e.g., engineered composite metamaterials, filters, etc.) and active (e.g., nanolasers) components on-chip, with the same lithographic tools as electronics. In this talk, we discuss some of the passive metamaterials and devices that recently have been demonstrated in our lab. These include our most recent results on monolithically integrated short pulse compressor utilized with SOI material platform and design, fabrication and testing of nanolasers constructed using metal-dielectricsemiconductor resonators confined in all three dimensions. |
| Title: | Publishing Physics in Science Magazine |
| Speaker: | Dr Ian Osborne |
| Date: | 8 July 2013 |
| Time: | 2pm - 3pm |
| Venue: | SPMS-LT1 (SPMS-04-07) |
| Host: | Professor Nikolay Zheludev |
| Abstract: | Science is the world's leading journal of original scientific research, global news, and commentary. Over all disciplines, the journal receives over 12000 research papers submitted each year for consideration for publication. In 2012, just over 1000 of those papers were in the areas of physics and applied physics. With only 80 or so papers in these areas selected for publication, the competition for that limited space is fierce. I will overview the selection and peer review process at the journal. |
| Title: | Nonlinear optical phononics: Harnessing sound and light in nonlinear nanoscale circuits |
| Speaker: | Professor Benjamin Eggleton |
| Date: | 5 July 2013 |
| Time: | 2pm - 3pm |
| Venue: | SPMS - LT4 (SPMS-03-09) |
| Host: | Assistant Professor Cesare Soci |
| Abstract: | Stimulated Brillouin Scattering (SBS), whereby light interacts coherently with acoustic phonons, is a powerful and
flexible mechanism for the control of light, having recently been used to achieve tunable slow-light as well as find
application in a range of important technologies such as Brillouin lasers, sensors, opto-mechanical oscillator and
tailoring optical forces. However, many of the demonstrations exploiting SBS use long length (~ km) silica fiber,
which is incompatible with photonic integration. In this talk, I review our recent development of a unique on-chip
SBS platform exploiting chalcogenide photonic circuits and highlight demonstrations of on-chip SBS slow-light,
SBS based microwave signal processing, chip based Brillouin lasers and non-reciprocal devices.
1. Christopher G. Poulton et al.,"Design for broadband on-chip isolator using stimulated Brillouin scattering in dispersionengineered chalcogenide waveguides," Opt. Express 20, 21235-21246 (2012). 2. Adam Byrnes et al. "Photonic chip based tunable and reconfigurable narrowband microwave photonic filter using stimulated Brillouin scattering," Opt. Express 20, 18836-18845 (2012). 3. Ravi Pant et al., "Photonic-chip-based tunable slow and fast light via stimulated Brillouin scattering," Opt. Lett. 37, 969-971 (2012). 4. Ravi Pant et al., "On-chip stimulated Brillouin scattering," Opt. Express 19, 8285-8290 (2011) 5. B. J. Eggleton, B. Luther-Davies, and K. Richardson, "Chalcogenide photonics," Nature Photonics, 5(3): p. 141-148 (2011) |
| Title: | Nanomaterials Design for Energy and Environment |
| Speaker: | Dr Yi Cui |
| Date: | 4 July 2013 |
| Time: | 11am - 12pm |
| Venue: | SPMS - LT4 (SPMS-03-09) |
| Host: | Assistant Professor Fan Hongjin |
| Abstract: | The development of nanotechnology in the past two decades has generated great capability of controlling materials at the nanometer scale and has enabled exciting opportunities to design materials with desirable photonic, electronic, ionic and mechanical properties, which are important for energy and environment technologies. In this talk, I will show how we design rationally nanostructured materials for these applications. Examples include: 1) high capacity nanostructured Si anodes. 2) high capacity nanostructured S cathodes. 3) 3D nanoelectrodes for microbial fuel cells. 4) High efficiency water filter for pathogen disinfection. |
| Title: | Colorful Science: From Beer Foam and Soap Films to Self-Assembled Structural Colors in Nature |
| Speaker: | Dr Vinod Saranathan |
| Date: | 20 June 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS- PAP-02-02) |
| Host: | Assistant Professor Chong Yidong |
| Abstract: | Many organisms produce vivid colors via optical interference from meso-scopic (100-350 nm) integumentary
features that are diverse in form and optical function. These, so-called, structural colors with millions of years
of evolutionary history, are ubiquitous in nature and constitute an important part of the phenotype of many
organisms, as they are frequently used in social and sexual signaling, aposematic communication,
camouflage, etc. Understanding the precise mechanistic basis of organismal nanostructures would not only
help biologists ascertain their biological function and evolution, but might also provide useful biomimetic
inspiration, given that the self-assembly of synthetic macromolecules at the optical length scales is
challenging. It is no wonder that biophotonic nanostructures are increasingly being looked into for
technological improvements and innovations.
In this lecture, I will present some fascinating insights gained from using synchrotron Small Angle X-ray Scattering (SAXS) into the structure, optical function, development and evolution of isotropic (non-iridescent) structural coloration in bird plumage, in addition to the weak to strongly directional (iridescent) coloration on the scales of many insect orders including butterflies, beetles, bees, and arachnids. Given the overwhelming diversity on many levels, an overarching theme, I will argue, in the development of these nanostructures is their apparent self-assembly via arrested phase separation and lyotropic membrane folding mechanisms. I will conclude with some preliminary results and lessons for the bio-inspired design of synthetic photonic materials. The self-assembly of biophotonic nanostructures in birds and insects offers a coherent and elegant explanation for the repeated independent evolution of distinctive and highly stereotypical nanostructures responsible for structural coloration in ecologically and evolutionarily diverse lineages. |
| Title: | Graphene-based, Graphene-derived, and New Carbon Materials |
| Speaker: | Professor Rodney S. Ruoff |
| Date: | 24 May 2013 |
| Time: | 10.30am - 11.30am |
| Venue: | Hilbert Space (SPMS- PAP-02-02) |
| Host: | Assistant Professor Yu Ting |
| Abstract: | Graphene-based materials are promising because of their electronic and thermal transport,
mechanical properties, high specific surface area, that they can act as an atom thick layer, barrier,
or membrane, among other reasons. (Our micromechanical exfoliation approaches [1,2]
conceived of in 1998 yielded multilayer graphene and one paper described in detail how
monolayer graphene could be obtained [1]). In addition to describing some of our recent work
on graphene, I will also discuss new materials as yet not made that are important targets for
materials synthesis: (i) the negative curvature carbons [3,4] and their likely applications, and (ii)
ultrathin and large area sp 3 carbon films [4].
Support of our work on graphene by the W. M. Keck Foundation, NSF, DARPA ‘iMINT’, DARPA ‘CERA’, ONR, SWAN NRI, ARO, AEC, and the SRC, is greatly appreciated. |
| Title: | Thermodynamics of Ultracold Gases |
| Speaker: | Professor Frederic Chevy |
| Date: | 16 May 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor David Wilkowski |
| Abstract: | The understanding of the properties of strongly correlated quantum systems is one of the most challenging open problems in modern physics, since it is relevant to fields as different as condensed matter, astrophysics or nuclear physics. Using the latest techniques of manipulation of ultracold vapors, it is now possible to probe the quantum many body problem using the tools of atomic physics. In this talk, I will show that it is possible to engineer model experimental systems reproducing faithfully some of the most popular hamiltonians used in theoretical physics. I will illustrate this on the study of the thermodynamic properties of strongly correlated gases that can now be benchmarked accurately using advanced experimental and theoretical techniques. |
| Title: | Light Harvesting: non-local and quantum tunnelling effects |
| Speaker: | Dr Luo Yu |
| Date: | 16 May 2013 |
| Time: | 2pm - 4pm |
| Venue: | MAS Executive Classroom 1 (SPMS- MAS-03-06) |
| Host: | Assistant Professor Zhang Baile |
| Abstract: | Metallic nanoparticles that support localized surface plasmon resonances can concentrate light into a deepsubwavelength volume, thereby achieving very large field enhancements. Many emerging nano-photonic technologies rely on the careful control of this field enhancement, including cancer therapy, improved photovoltaic devices, and optical antennas for enhanced light-matter interactions. However, at deep subwavelength scales, classical continuum electrodynamics fails to describe the optical responses of nanoparticles owing to nonlocal screening and the spill-out of electrons. Electron correlations that are driven by these effects require a new model of nonlocal transport, which is crucial in nanoscale optoelectronics. In this talk, I will present a systematic strategy, based on transformation optics, to study analytically the plasmonic interaction at subnanometer scales. Our approach incorporates radiative, nonlocal, and quantum tunnelling effects, and thus can be applied to design realistically sized plasmonic systems. As an example, I will use this method to elucidate the optimum shape of a nanoparticle that maximizes its absorption and field enhancement capabilities. |
| Title: | Transformation Optics and the control of light |
| Speaker: | Dr Luo Yu |
| Date: | 16 May 2013 |
| Time: | 10am - 12pm |
| Venue: | MAS Executive Classroom 1 (SPMS- MAS-03-06) |
| Host: | Assistant Professor Zhang Baile |
| Abstract: | Transformation optics as a tool has generated much interest in recent years. It offers revolutionary ways to manipulate light (from radio frequencies to the visible) and also other forms of electromagnetic waves, such as the surface plasmons. Among the plethora of its applications, it is perhaps the demonstration of invisibility cloak that has sparked the greatest excitement. Other novel applications of Transformation optics, involves the direct manipulation of EM waves, and these include the flatten Luneburg lens, super-scatterers, field rotators, just to name a few. The application of Transformation optics in plasmonics has also generated new developments, such as surface plasmon guiding and focusing. The possibility of manipulating surface plasmons has open up more alternative means of information transfer beyond the traditional electron transport, promising much faster data transfer rates. The ability to focus surface plasmons can also vastly improve the sensitivities of chemical detectors and enhance the efficiencies of photovoltaic devices. Indeed, this new strategy of manipulating light has posed fascinating possibilities and challenges for experimentalists and theorists, driving forward new techniques and conceptual approaches to old problems. In this talk, I will talk about the progress in the study of transformation optics, and the resolution to the challenges of realizing these ideas. The focus of the talk would be on how to simplify the required material parameters while optimizing the performance of Transformation optics devices. Specifically, I will highlight a special sub-class of transformations, i.e. linear transformations, which enables devices to be more easily implemented using natural birefringent crystals or homogeneous grating structures. As examples, I will show how to design macroscopic invisibility cloak at optical frequencies, full-parameter omni-directional cloak, broadband SPP bending structures, and abrupt SPP focusing, using these linear transformations. |
| Title: | Controlling waves at subwavelength scales in space and time through complex media : from acoustics to optics |
| Speaker: | Professor Mathias Fink |
| Date: | 8 May 2013 |
| Time: | 4pm - 5pm |
| Venue: | MAS Executive Classroom 1 (SPMS- MAS-03-06) |
| Host: | Associate Professor Claus Dieter Ohl |
| Abstract: | According to time-reversal symmetry, a broadband wave can be focused both in time and space regardless of the complexity of a scattering medium. The broadband nature of time-reversed waves distinguishes them from continuous phase-conjugated waves and allows revisiting the origin of diffraction limits, suggesting different ways to obtained subwavelength focusing. The first approach consists in introducing absorbing resonators that act as perfect absorbers. A second approach uses media made of coupled subwavelength resonators. These various approaches are very different from the one developed with superlenses made of negative index material that are only valid for narrowband signals. We will emphasize the role of the frequency diversity and a modal description of the spatio-temporal focusing will be presented. A review of this field with acoustic, elastic, electromagnetic and optical waves will be presented. |
| Title: | The Journey of Basic Science to Translational Science: Development of handheld Magnetic Resonance Relaxometry System for Medical Diagnosis |
| Speaker: | Dr Peng Weng Kung |
| Date: | 7 May 2013 |
| Time: | 4pm to 5pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Assistant Professor Zhang Baile |
| Abstract: | With advances in microelectronics technology, Magnetic Resonance (MR) community sees the emergence of much more compact MR spectrometers on a highly integrated circuit platform such as field programmable gate array (FPGA), and complementary-metal oxide semiconductor (CMOS). Here, in SMART Centre, Singapore, a novel, compact-sized, and portable (250g) Magnetic Resonance Relaxometry system is designed and developed. The whole system consists of a coin-sized permanent magnet (0.76 Tesla), miniaturized radio-frequency microcoil probe, compact lumped-circuit duplexer, and single board 4-Watt power amplifier, in which a FPGA-based spectrometer is used for pulse excitation, signal acquisition and data processing. We show that by measuring the proton transverse relaxation rates from a large pool of natural abundance proton-nuclei presence in less than 1 µL of red blood cells, one can indirectly deduce the relative magnetic susceptibility of the bulk cells within a few minutes of signal acquisition time. Such rapid and sensitive blood screening system can be used to monitor the fluctuation of the bulk magnetic susceptibility of the biological cells (e.g. human red blood cells), where unusual state of the bulk magnetic susceptibility is related to a number of diseases (e.g. malaria, sepsis, genetic diseases, etc). We are looking to commercialize this technology & research collaboration on various aspects of diseases, or drug screening applications |
| Title: | Directional light scattering by dielectric nanoparticles |
| Speaker: | Professor Boris LUKIYANCHUK |
| Date: | 6 May 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Professor Shen Zexiang |
| Abstract: | Directional light scattering by spherical silicon nanoparticle in the visible spectral range is experimentally
demonstrated for the first time. These unique optical properties arise because of simultaneous excitation and
mutual interference of magnetic and electric dipole resonances inside a single nanosphere. Such behavior is
similar to Kerker’s-type scattering by hypothetic magneto-dielectric particles predicted theoretically three decades
ago. Here we show that directivity of the far-field radiation pattern of single silicon spheres can be strongly
dependent on the light wavelength and the nanoparticle size. For nanoparticles with sizes ranging from 100 to 200
nm, forward-to-backward scattering ratio above six can be experimentally obtained, making them similar to
‘Huygens’ sources. Unique optical properties of silicon nanoparticles make them promising for design of novel lowloss visible- and telecom-range metamaterials and nanoantenna devices.
Y.H. Fu, A. I. Kuznetsov, A. E. Miroshnichenko, Y. F. Yu and B. Luk’yanchuk, Nature Communications 4, 1527 (2013) |
| Title: | Human propeller telomeric DNA Quadruplex: Plastic or Elastic ? |
| Speaker: | Dr Shozeb Haider |
| Date: | 3 May 2013 |
| Time: | 11am - 12pm |
| Venue: | Hilbert Space (SPMS- PAP-02-02) |
| Host: | Associate Professor Phan Anh Tuan |
| Abstract: | The human telomeric DNA sequence with four repeats can fold into a parallel-stranded propeller-type topology. This topology has been used for rationalization of ligand design and occurs experimentally in a number of complexes with a diversity of ligands, at least in the crystalline state. Although G-quartet stems have been well characterized, the interactions of the TTA loop with the G-quartets are much less defined. To better understand the conformational variability and structural dynamics of the propeller-type topology, we performed molecular dynamics simulations in explicit solvent up to 1.5 μs. The benchmark simulations challenges the concept of plasticity associated with this topology. |
| Title: | Semiconductor Nanowires: Ideal Bridge between Macro and Microscopic Worlds |
| Speaker: | Professor YU Dapeng |
| Date: | 2 May 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Xiong Qihua |
| Abstract: | Nanowires have been a top-five focused research topics in physics, and stimulated intensive interests world-wide. This lecture composes of two major parts. In the first part, I will give a brief summary of our contributions to the world-wide nanowire research. In the second part, I will extend to show the advantage of both high spatial and energy resolution cathodoluminescence (CL) in characterization of the fine structures of the nanomaterials. In particularly, I will demonstrate that the high special resolution of the CL at ~ 5.5 K enable us to address the significant strain modulation of the optical emission and electronic structures of semiconductor nano/micro wires. In contrast, the high energy resolution of the CL makes it possible to “see” directly the resonant SPP modes that are confined to the metal nanocavity. |
| Title: | Information Processing with Belousov-Zhabotinsky Reaction |
| Speaker: | Professor Jerzy Gorecki |
| Date: | 2 May 2013 |
| Time: | 11am - 12pm |
| Venue: | MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | Assistant Professor Tomasz Paterek |
| Abstract: | It is well known that the time evolution of concentrations of reagents of Belousov-Zhabotinsky reaction can be
interpreted as a sequence of information processing operations. In the case of ferroin catalyzed reaction two states
of the medium, corresponding to high concentrations of the catalyst in the reduced or the oxidized forms can be
easily distinguished by the medium color. We can assign the logical "TRUE" state to a high concentration of the
oxidized catalyst and the other state to the logical "FALSE". Information can be coded in propagating pulses of
excitation and it is processed in regions of medium where pulses interact. In reaction-diffusion computing the
geometrical structure of chemical medium is equally important as chemical dynamics because it has a significant
influence on interactions between excitations. I will demonstrate that computing based on Belousov-Zhabotinsky
reaction is universal and all logic gates can be constructed with the proper geometry of excitable and non-excitable
regions. Alternatively one can use frequency of chemical oscillations for information coding. It can be also shown
that all logic gates for such information coding can be constructed using a chemical medium.
It seems especially interesting to self-generate chemical information processing structures at carefully selected nonequilibrium conditions. We hope that such self-generation will be possible in a medium composed of lipidcovered droplets containing reagents of Belousov-Zhabotinsky reaction. The lipid-covered BZ droplets can interact via exchange of reagents through the separating lipid layer and the surrounding hydrocarbons. The structure of multiple droplets can be regarded as a prototype of a neural network, where individual droplets play the role of nonlinear elements (neurons) that are linked together and communicate . |
| Title: | Metrology of acoustics and industrial ultrasound |
| Speaker: | Dr Christian Koch |
| Date: | 30 April 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor Claus-Dieter Ohl |
| Abstract: | Metrology, the science of measurement is a prerequisite of modern technological development and is required in the whole field of medicine and technology. The Physikalisch-Technische Bundesanstalt (PTB) is the national metrology institute of Germany providing scientific and technical services also for acoustics and ultrasound. The talk introduces into the activities of the department Sound with particular focus on industrial ultrasound. Investigations about the safety of phacoemulsification devices, a sensor for the quantitative determination of cleaning efficiency in ultrasonic vessels are presented together with measurement techniques for the measurement and assessment of airborne ultrasound. |
| Title: | Optimization of artificial flocks by means of anisotropy measurements |
| Speaker: | Dr Jun-ichi Inoue |
| Date: | 30 April 2013 |
| Time: | 11am - 12pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Cheong Siew Ann |
| Abstract: | An effective procedure to determine the optimal parameters appearing in artificial flocks is proposed in terms of an
optimization problem. We numerically examine genetic algorithms (GAs) to determine the optimal set of
parameters such as the weights for three essential interactions in Boids, which is a coined word ``Birdoids''
inspired by ``Android'' [1], under `zero-collision' and `no-breaking-up' constraints. As a fitness function to be
maximized by the GA, we choose the so-called the gamma-value of anisotropy which can be observed empirically
in typical flocks of starling [2]. We confirm that the GA successfully finds the solution having a large gamma-value
leading-up to a strong anisotropy even if the set of weights is homogeneous. The numerical experience shows that
the procedure might enable us to make more realistic and efficient artificial flocks of starling. We also evaluate two
distinct types of interactions in agents, namely, metric and topological definitions of interactions. We confirm that
the topological definition can explain the empirical evidence much better than the metric definition does.
[1] http://www.red3d.com/cwr/boids/ C.W. Reynolds, Flocks, Herds, and Schools: A Distributed Behavioral Model, Computer Graphics, Vol.21, pp.25-34 (1987). [2] M. Ballerini et.al, Interaction Ruling Animal Collective Behaviour Depends on Topological rather than Metric Distance, Evidence from a Field Study, PNAS, Vol.105, No.4, pp.1232-1237 (2008). |
| Title: | Systemic Risk - DebtRank Analysis of Credit Networks in Japan |
| Speaker: | Professor Hideaki Aoyama |
| Date: | 30 April 2013 |
| Time: | 10am - 11am |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Cheong Siew Ann |
| Abstract: | In this work, we study a comprehensive Japanese economic network of banks and firms (nodes) with links representing the lending/borrowing relationships between the banks and the firms. We examine these relationships in order to identify key nodes in regard to the risk levels that they impose on the bank-firm system. By assigning some level of distress to a bank and letting the distress propagate to other nodes according to relative node exposures to the distressed bank, we find the level of threat that the bank poses to the entire system. We quantify the systemic importance of banks on one hand and firms on the other by the DebtRank centrality measure. Moreover, by combining DebtRank and Herfindahl index of distress distributions, we identify two categories of key banks: the large city banks with high impact on other banks, and small but important regional banks with large impact on the firms. |
| Title: | Chained Financial Failures at Nation-wide Scale in Japan |
| Speaker: | Professor Yoshi Fujiwara |
| Date: | 30 April 2013 |
| Time: | 10am - 11am |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Cheong Siew Ann |
| Abstract: | I will talk about recent studies based on real data of propagation of financial failures in the past financial crises and the present one due to the earthquake at nation-wide scales in Japan. Leading credit research agencies in Tokyo and Nikkei have accumulated a huge amount of data on banks-firms and supplier customer links with financial information and failures of nodes. By using these large-scale data, we measure the actually occurred propagation of financial distress on the real data of large-scale economic networks comprising of firms, banks, and their relationships at the order of millions and even more. Exogenous shocks due to global financial crisis and mass destruction by disasters such as earthquakes cause propagation resulting in a sluggish relaxation, typically observed as an Omori-law. |
| Title: | Econophysics of Income & Wealth Distributions in Societies |
| Speaker: | Dr Bikas K. Chakrabarti |
| Date: | 29 April 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Cheong Siew Ann |
| Abstract: | Increasingly, a huge amount of statistics have been gathered which clearly indicates that income and wealth distributions in various countries or societies follow a robust pattern, close to the Gibbs distribution of energy in an ideal gas in equilibrium. However, it also deviates in the low income and more significantly for the high income ranges. Application of physics models provides illuminating ideas and understanding, complementing the observations. We intend to discuss these recent developments. |
| Title: | Multi-step simulation of natural and modified DNAs |
| Speaker: | Dr Rosa Di Felice |
| Date: | 17 April 2013 |
| Time: | 3.30pm - 4.30pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Professor Maria E. Michel Beyerle |
| Abstract: | I present viable theoretical strategies based on computer simulations to tackle complex biological systems including dynamical and environment effects. In this talk I focus on the electronic structure of DNA molecules with structural and chemical alterations. I briefly motivate the problem. Then I develop my work on this issue, based on density functional theory and classical molecular dynamics, with force field development when needed. I show the results of DFT calculations on frozen DNA-based fragments and the evidence that a single structure fails to render the whole picture. I then illustrate a possible multi-step approach to take into account the dynamical flexibility of the molecules in solution and results of this approach for specific cases of modified DNA (e.g., triplex DNA, duplex DNA with non-natural bases). I finally draw general methodological conclusions and identify further development of the proposed themes. |
| Title: | Enhancement of Network Resilience with Optimizing Topologies |
| Speaker: | Professor Akira Namatame |
| Date: | 11 April 2013 |
| Time: | 3pm - 4pm |
| Venue: | MAS Executive Classroom 1 (MAS-03-06) |
| Host: | Assistant Professor Cheong Siew Ann |
| Abstract: | The increasing scale and complexity of networked systems has necessitated an approach for network resilience and
robustness. Since the network topology has a direct impact on performance such as resilience and robustness, a
mechanism of self-control is also an important and immediate requirement. The network topology is the most
fundamental network property on which self-control is deployed, and the control over the topology has a direct impact on
network performances. The network topology impacts on failure spread in networks. The issue of enhancing network
resilience could be analyzed with optimizing the underlying network topology.
Network science has attracted considerable attention over the last decade. Two principal approaches have contributed to understanding complex networks so far. The first is an assembly mechanism that derives the structure of large-scale networks from processes that describe the piecewise addition of nodes and links according to simple heuristic rules such as preferential attachment. The second approach is via an optimization principle that aims at optimizing network performance through its evolution. Traditionally, optimization has a strict mathematical definition, which refers to obtaining the solutions that strictly specialize a well-defined function. Here we adopt a looser definition by extending it to include a tendency of the network to improve its performance as a result of evolution. We define metrics on network robustness and resilience and formulate multi-criteria network optimization problems. We use generic algorithm (GA) to solve these optimization problems and obtain optimal network topologies. Many real-world problems are complex with a very large parameter space. Accordingly, most attempts for finding the best solution are not realistic. In stead, finding a good enough solution or a better solution in an iterative manner becomes alternative. Both the most susceptible network and the least susceptible networks to cascading failure are obtained using generic optimization and their network topologies are characterized and these networks are characterized. The least susceptible network to minimize cascade failure or systemic risk in financial networks is characterized as a core-periphery network. Such a core-periphery network consists of a partial complete graph of core nodes and stub nodes connected only to the core nodes. We also obtain the most susceptible network to cascade failure. The most susceptible network is characterized as an onion-like network, in which nodes with similar degrees are more likely connected. However the most susceptible network to cascade failure has the highest robustness to random and intentional node attack. |
| Title: | Composite Model of the Weak Bosons |
| Speaker: | Professor Harald Fritzsch |
| Date: | 4 April 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor Claus Dieter Ohl |
| Abstract: | The weak bosons are considered as composite particles. The masses of the weak bosons are given by the field energy of the constituents. A Higgs particle is not needed. The boson, observed at the LHC, is a p wave excitation of the Z boson. The other p wave excitations have a higher mass and should soon be observed at the LHC. |
| Title: | Thin Films and Superlattices of Manganite Perovskites: Role of Transmission Electron Microscopy |
| Speaker: | Dr Oleg Lebedev |
| Date: | 28 March 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Tom Wu |
| Abstract: | Thin films and SLs give a unique opportunity to tune the structure and properties of perovskite oxides. Advanced transmission electron microscopy (TEM) addresses the structure and chemical composition of the SLs in detail by means of electron diffraction (ED), high resolution transmission electron microscopy (HRTEM), aberrationcorrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) down to the atomic scale. A few examples will be discussed in this talk. A-site ordered colossal magnetoresistant epitaxial La3/4Ca1/4MnO3 /MgO(100) (LCMO) thin films were epitaxially grown on MgO(100) substrate. TEM observations revealed a pseudo-cubic (R-3c) structure, unusual for LCMO, with a new perovskite superstructure due to the unique ordering of La and Ca at the A-site positions. A-site ordered films were found to be electronically homogeneous down to the 1 nm scale as revealed by scanning tunnelling microscopy/spectroscopy. In contrast, orthorhombic and A-site disordered LCMO demonstrate a mesoscopic phase separation far below the Curie temperature (Tc). A specific 3D La/Ca ordering of the CE-type suppresses the cation mismatch stress, enhancing the electronic homogeneity and enhance CMR=500 %. As another example, (La2/3Ca1/3MnO3 )n/(BaTiO3 )m (LCMOn/BTOm) superlattices on MgO and SrTiO3 substrates with different layer thicknesses (n= 10, 38, 40 and m = 5, 18, 20) have been grown by metalorganic aerosol deposition. Scanning transmission electron microscopy combined with spatially resolved electron energy-loss spectroscopy provides clear evidence on the existence of atomically sharp interfaces. Below a critical layer thickness the LCMO structure is found to change from the bulk Pnma symmetry to a pseudocubic R-3c symmetry. An atomically flat interface reconstruction consisting of a single Ca-rich atomic layer is observed for the first time on the compressively strained BTO on LCMO interface, which is thought to partially neutralise the total charge from the alternating polar atomic layers in LCMO as well as relieving strain at the interface. The observed structural differences infer the presence of magnetically dead interface layers and evidence the importance of electronic and lattice correlations at perovskite interfaces. |
| Title: | Advance Transmisson Electron Microscopy and Nanoarchitectures |
| Speaker: | Dr Oleg Lebedev |
| Date: | 26 March 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Tom Wu |
| Abstract: | The world of nanotechnology has become something of a fashion statement in recent years, and products using the term “nano” are now abundant. Transmission electron microscopy (TEM) is one of the most reliable and powerful technique to measure nanoachitectures. In this talk, I will discuss first hybrid diamond-graphite nanowires as structural units in UNCD films synthesized by CVD. This hybrid material consist of a single crystalline diamond core of 5–6 nm in diameter oriented along the [110] principal axis and graphitic shells of different thickness covering the core. The I will discuss Si nanowires (NWs), which were synthesized by vapor-liquid-solid process, and exhibit sawtooth facets containing Au adsorbates. The sidewalls are covered with Au-rich nanoclusters. Their facets also exhibit atomic structures that reveal the presence of gold, resulting from the diffusion of gold during the growth. Recently, Zn4O(bdc)3 (MOF-5) crystals have been loaded with catalytically active material like Pd, Au, Cu and Ru leading to a heightened catalytic activity in olefin hydrogenolysis and methanol synthesis. The loading procedure is known to yield a MOF-5 framework loaded with catalytically active NPs in the range of 1-3 nm. The local distribution of these particles within the MOF-5 framework however remains unclear. In this talk I will show that by minimising the electron dose to avoid beam damage, TEM can be used to characterise this new family of soft materials on a local scale. Finally, I will discuss novel dual-metal Au-Cu alloy and Au nanoparticles (NPs) which were used as a catalyst for tin-doped indium oxide (ITO) NW growth. They was characterised by advance TEM techniques including high resolution TEM (HRTEM) , electron diffraction (ED), energy dispersive X-ray (EDX) , high angle annular dark field scanning TEM (HAADF) and electron energy-loss spectroscopy (EELS). The dynamically tuned chemical potentials in the catalyst NPs selectively stabilize a rare cubic indium-tin-oxide phase (ISO) revealed by TEM, forming epitaxial heterojunctions within individual NW branches. |
| Title: | Computational Problems and Practical Receivers for Photons |
| Speaker: | Dr Si-Hui Tan |
| Date: | 21 March 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Tomasz Paterek |
| Abstract: | Quantum optics is a fertile ground for implementing quantum computing and communication protocols. Nowadays, the
production of photonic sources, circuits, and measurements is the bread-and-butter of many laboratories around the
world. Many new quantum protocols are not only achieved with optical implementations but may become an everyday
reality using existing technologies such as the optical fiber infrastructure. The use of quantum mechanics promises
security, efficiency and information transfer rates that are not possible with only classical mechanics.
I will first analyze a computing problem for photons—the BosonSampling problem—that proposes that single photons and linear optical networks be used for computing the permanents of unitary matrices. Computing permanents is a problem known to be #P-Complete, which is harder than NP. I will develop a framework for solving the action of a three-channel passive optical interferometer on single-photon pulse inputs to each channel using SU(3) grouptheoretic methods. I will demonstrate that we can not only measure permanents of matrices but also their immanants. This framework makes it easy to construct interferometers from beamsplitters and phase-shifters to give specific features that would be interesting. For instance, I will show how an interferometer can be constructed to give a threephoton Hong-Ou-Mandel dip. This framework can also be readily generalized to higher-order photon-coincidence experiments. For measuring photons with practical receivers, I will discuss the Sequential Waveform Nulling (SWN) receiver, which discriminates between states of an arbitrary coherent-state ensemble using only auxiliary coherent-state fields, beamsplitters, and non-number-resolving single photon detectors. I will derive the quantum limit on the error probability exponent for discriminating among any M multimode coherent-state waveforms and show that the SWN receiver achieves this quantum limit. As coherent-states are central to applications of laser light, such as quantum imaging and sensing, the SWN receiver will be important for these applications as a practical receiver. Finally, I will demonstrate the performance of the SWN receiver on a phase-shift-key coherent-state ensemble and compare it to the performance of other known coherent-state receivers. |
| Title: | Towards Light Bullets in Vertical-Cavity Surface-Emitting Lasers |
| Speaker: | Professor Massimo Giudici |
| Date: | 20 March 2013 |
| Time: | 2pm - 3pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor Sun Handong |
| Abstract: | Spatio-temporal solitons, also called “light-bullets” (LB) have been actively sought in the last 20 years. Despite the efforts made, only fading spatio-temporal light pulses were experimentally observed in a waveguide array. At INLN we propose an alternative approach to LB based on self-organisation of dissipative systems. While in waveguides LB existence and stability rely heavily on sensitive balance of non-linearities and on specific characteristics of the seeding pulses, three dimensions localized states of light may exist in dissipative systems as stable solutions (attractors) towards which the system would spontaneously evolve. In order to reach three dimensional localization of light we build on the results achieved on spatial localization (Cavity Solitons Laser) and time localization (Mode-locked Laser). The results we have obtained so far will be presented. |
| Title: | Cesium Beam Clock and Magnetometer |
| Speaker: | Professor Yanhui Wang |
| Date: | 14 March 2013 |
| Time: | 4.30pm - 5.30pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Rainer Dumke |
| Abstract: | Traditional cesium clocks include two types. One is the magnet-selected and electron multiplier, the other is the optically-pumped and optically-detected. We propose a new type: magnet-selected and optically-pumped with one new absorbed cell design, which has some advantages. I will present some recent results on it. I will also talk about some initial work on the cesium magnetometer in our group |
| Title: | Quantum Entanglement and Thermodynamics |
| Speaker: | Professor Vlatko Vedral |
| Date: | 28 February 2013 |
| Time: | 11am - 12pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Dr Ho Shen Yong |
| Abstract: | I will talk about the impact of temporal entanglement on a system’s ability to perform thermodynamical work. I will introduce the Jarzynski equality and argue that, while the quantum version of the Jarzynski equality remains satisfied even in the presence of temporal entanglement, the individual thermodynamical work moments in the expansion of the free energy are, in fact, sensitive to the genuine quantum correlations. While individual moments of the amount of thermodynamical work can be larger (or smaller) quantumly than classically, when they are all combined together into the (exponential of) free energy, the total effect vanishes to leave the Jarzynski equality intact. Whether this is a fortuitous coincidence remains to be seen, but it certainly goes towards explaining why the laws of thermodynamics happen to be so robust as to be independent of the underlying micro-physics. I intend to discuss the relationship between this result and thermodynamical witnesses of spatial entanglement as well as explore the subtle connection with the “quantum arrow of time”. |
| Title: | (1) Spin conduction in anisotropic 3‐D topological insulators, and (2) Anomalous spin diffusion in strained hole doped systems |
| Speaker: | Dr Vincent E. Sacksteder IV |
| Date: | 4 February 2013 |
| Time: | 1pm - 2pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Wang Lan |
| Abstract: | In the first part of this talk we show that in anisotropic topological insulators the spin
lifetime can be much larger than the scattering time. Two different mechanisms can produce
this effect. The first is tuning the Hamiltonian to conserve a spin operator cos φ σx + sin φ σy ,
while the second is tuning the Fermi energy to be near a local extremum of the energy
dispersion. Both mechanisms can produce persistent spin helices.
In the second part of this talk we obtain the spin‐orbit interaction and spin diffusion equations of
a two‐dimensional heavy hole gas under the influence of strain. We predict
an enhanced spin lifetime associated with a spin helix standing wave similar to
the Persistent Spin Helix which exists in the two‐dimensional electron gas with equal
Rashba and Dresselhaus spin‐orbit interactions.
Collaborators: Stefan Kettemann, Quansheng Wu, Xi Dai, Zhong Fang, Andrei Bernevig |
| Title: | Optical Integrated Circuits based on Exciton-Polaritons |
| Speaker: | Professor Alexey Kavokin |
| Date: | 1 February 2013 |
| Time: | 11am - 12pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Cesare Soci, Associate Professor Ivan Shelyk |
| Abstract: | Exciton-polaritons are mixed light-matter quasiparticles combining properties of photons and excitons. The Bose-Einstein condensation of exciton-polaritons results in a spontaneous emission of a coherent light, or polariton lasing. Polariton lasers with optical pumping have been realized in GaAs, CdTe and GaN based planar and pillar microcavities. They represent the first class of opto-electronic devices based on exciton-polaritons and possess unique characteristics including the ultra-low threshold power, controllable polarization of emission, peculiar statistics of emitted photons . So far only optically pumped polariton lasers have been realized while very detailed proposals on the design of electrically pumped polariton lasers have been published (figure). Several other types of polariton devices are being developed.
Experimentally, GaAs-microcavity based electrically pumped polariton
diodes , optical parametric oscillators , optical switches and optical logic
gates have been already realized. The theoretical proposals go farther
evoking the possibility of building of all-optical integrated circuits based
on polariton neurons . These devices would exploit giant optical nonlinearities induced by polariton condensates: the optical bi-stability or
multi-stability appearing due to these resonant non-linear effect allows for
formation of domains of high polariton concentration. These domains may
be spin-polarised. The information transfer in polariton neurons is due to
the ultrafast motion of the domain walls. |
| Title: | Theoretical Modeling of Electronic, Optical, and Doping Properties of Oxides for Energy Applications |
| Speaker: | Professor Su-Huai Wei |
| Date: | 30 January 2013 |
| Time: | 2pm - 3pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Professor Shen Zexiang |
| Abstract: | Post-transition metal oxides (ZnO, In2O3, SnO2, TiO2, etc.) play an essential role in modern optoelectronic devices because they have many unique physical properties such as structure diversity, superb stability in solution, good catalytic activity, and simultaneous high electron conductivity and optical transmission. Therefore, they are widely used in energy related optoelectronic applications such as photovoltaics and photoelectrochemical (PEC) water splitting. In this work, using first-principles band structure calculations, we will study the electronic, optical, and doping properties of oxides and address some questions related to the unique materials properties of the oxides, including (i) why most of the transparent conducting oxides (TCOs) are n-type and what kind of band structures are good for n-type TCOs? (ii) Are oxygen vacancy an efficient intrinsic n-type dopants (i.e., are the defect levels deep or shallow) in metal oxides? (iii) To achieve optimal n-type conductivity through extrinsic doping, should we choose dopant substituting on anion site or cation site? (iv) Should the doping be done under oxygen-poor or oxygen-rich condition? (v) Why amorphous TCO can have good electrical conductivity even without passivation? And (vi) how to modify the band structure of oxides through defect control for PEC water splitting? |
| Title: | Nonlinear Photonic Crystals and their applications for Optical Signal Processing |
| Speaker: | Dr Alfredo De Rossi, Professor Xavier Checoury |
| Date: | 29 January 2013, 31 January 2013 |
| Time: | 2pm - 4pm, 11am - 1pm |
| Venue: | MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | Assistant Professor Cesare Soci |
| Abstract: | Very recently IBM advertised their new technology, called “silicon nanophotonics”, where optical and electrical signal will coexist on a single silicon die. That is only the latest of a series of impressive breakthroughs which have revolutionized photonics in the last decade. Photonic crystal is a particular photonic nanotechnology which has much progressed in the last years and which is likely to fit in this scheme. Photonic crystals bring specific functionalities, related to the enhancement of the light-matter interaction and the control of the dispersion which are very specific and valuable. We will briefly discuss photonic crystals and how they relate to the emerging field of nanophotonics for signal processing |
| Title: | Charge Order in Oxides: The Grin of the Cheshire Cat |
| Speaker: | Professor Warren Pickett |
| Date: | 24 January 2013 |
| Time: | 4pm - 5.30pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Pinaki Sengupta |
| Abstract: | While the formal valence and charge state concepts have been tremendously important in materials
physics and chemistry, their very loose connection to actual charge leads to uncertainties in
modeling behavior and interpreting data. We point out, taking several transition metal oxides
(La2VCuO6
, YNiO3
, CaFeO3
, AgNiO2
, V4O7
) as examples, that while dividing the crystal charge into
atomic contributions is an ill-posed activity, the 3d occupation of a cation (and more particularly,
differences) is readily available in first principles calculations. We discuss these examples, which
include distinct charge states and charge-order (or disproportionation) systems, where different
``charge states'' of cations have identical 3d orbital occupation. Implications for theoretical modeling
of such charge states and charge-ordering mechanisms are discussed.
Acknowledgments: Y. Quan, V. Pardo |
| Title: | Applying the Methods of Physics to Education Research |
| Speaker: | Dr David M. Harrison |
| Date: | 18 January 2013 |
| Time: | 3pm - 4pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Dr Ho Shen Yong |
| Abstract: | Over the past couple of decades, some physicists have applied the methods of physics research to the problem of determining what works and what does not work in educating their students. This has led to a whole field of research called Physics Education Research (PER), and the results have led to a worldwide movement of implementing “research-based pedagogy.” In this discussion, we will investigate Physics Education Research and how the results are implemented. We will also explore the “wrong” ideas and conceptual misunderstandings of our students. Finally, we will consider the fact that some colleagues, although aware of the research, have not implemented the results in their own classrooms. |
| Title: | Whither is the correlated oxide Interface? |
| Speaker: | Professor Jak Chakhalian |
| Date: | 18 January 2013 |
| Time: | 11am -12pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Tom Wu |
| Abstract: | Complex oxides are a class of materials characterized by a variety of competing interactions that create a
subtle balance to define the lowest energy state and lead to a wide diversity of intriguing properties ranging
from high Tc superconductivity to exotic magnetism and orbital phenomena. By utilizing the bulk properties
of these materials as a starting point, interfaces between different classes of complex oxides offer a unique
opportunity to break the fundamental symmetries present in the bulk and alter the local environment. Utilizing our
recent advances in oxide growth, we can now combine materials with distinct or even antagonistic order
parameters to create new materials in the form of heterostructures with atomic layer precision. The broken lattice
symmetry, strain, and altered chemical and electronic environments at the interfaces then provide a
unique laboratory to manipulate this subtle balance and enable novel quantum states not attainable in
bulk. Understanding of these phases however requires detailed microscopic studies of the heterostructure
properties. In this talk I will summarize our recent work on unit-cell thin nickelate heterostructures to illustrate
recently uncovered principles of rational materials design and control of interactions by the interface.
Selected references for the talk: J. Chakhalian et al, Science, v. 314, 1114, (2007). Jian Liu et al, Phys. Rev. B 83, 161102(R) (2011). J. Freeland et al, Europhys. Letters, 96 (2011) 57004. J. Chakhalian et al, Phys. Rev. Letters, 107 116805 (2011). J. Chakhalian et al, Nature Materials 11, 92–94 (2012). |
| Title: | Spin-1 antiferromagnets with single-ion anisotropy |
| Speaker: | Dr Yasuyuki Kato |
| Date: | 17 January 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Pinaki Sengupta |
| Abstract: | I will discuss the zero-temperature phase diagrams and low-energy excitations of spin-1 antiferromagnets
with a single-ion anisotropy on square and simple cubic lattices [1,2]. For easy- plane anisotropy, we
combine a generalized spin wave approach and large scale QMC simulations to study the nature
of the different phases and quantum phase transitions. We consider two alternative approaches for
describing the quantum paramagnetic state: the standard Holstein-Primakoff approximation and a
modified treatment in which the local Hilbert space constraint is enforced by introducing a Lagrange
multiplier. While both approximations produce qualitatively similar results, the latter approach is the
only one that is in good quantitative agreement with the phase diagram and the quasiparticle
dispersions obtained with QMC. For easy-axis anisotropy, we find a transition between XY-antiferromagnetic and ferronematic phases that spontaneously break the U(1) symmetry of the model. In
the language of bosonic gases, this is a transition between a Bose-Einstein condensate (BEC) of single
bosons and a BEC of pairs. Furthermore, we find three-magnon bound states that satisfy the Efimov
scaling at the point where the two-magnon s-wave scattering length becomes infinite [3].
Reference: [1] Zhang, Yap, Wierschem, Kato, Batista, & Sengupta (in preparation). [2] Wierschem, Kato, Nishida, Batista, & Sengupta, arXiv:1209.0688 (Phys. Rev. B). [3] Nishida, Kato, & Batista, arXiv:1208.6214 (Nature Physics, in press) |
| Title: | Mathematical formulations of radiative heat transfer |
| Speaker: | Professor Steven G. Johnson |
| Date: | 10 January 2013 |
| Time: | 4pm - 5.30pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Chong Yidong |
| Abstract: | Radiative heat transfer is a familiar fact of everyday life, from feeling warmed by the distant sun to seeing the red glow of hot metal in an electric burner. Although basic descriptions of this phenomenon have been available since Kirchhoff in the 19th century, following work by Newton and many others, understanding heat transfer becomes surprisingly complicated in microscale and nanoscale systems, where separations and geometries are on the scale of the thermal wavelength. As recently as a few years ago, solutions in this regime (even purely computational solutions) were known only for the simplest high-symmetry geometries such as parallel planes or pairs of spheres. This talk will introduce the challenges posed by radiative transport, assuming only basic knowledge of electromagnetism and no knowledge of thermodynamics, and explain new formulations of this problem that exploit connections to reciprocity and equivalence theorems in wave theory |
| Title: | Interfacial Phenomena in Soft Matter and Biophysics |
| Speaker: | Dr Halim Kusumaatmaja |
| Date: | 9 January 2013 |
| Time: | 4pm - 5pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor Claus-Dieter Ohl |
| Abstract: | In this seminar I will discuss two biologically inspired problems in interfacial phenomena. Firstly, I describe a novel soft matter system consisting of lipid vesicles and phase separating polymer solutions. Our theoretical analysis predicts the existence of an intrinsic contact angle between the membranes and the aqueous phases, reminiscent to Young's angle in standard wetting phenomena. An explicit relation is derived by which the intrinsic angle can be determined from experimental observables, and comparison between theory and experiment provides strong evidence that this intrinsic contact angle is a material parameter. I then use the theory to explain the budding transition – where one of the aqueous phases protrudes from the vesicle body – and the formation of membrane nanotubes observed in these systems. Secondly, I present lattice Boltzmann simulation results of droplets spreading and moving across anisotropic patterned surfaces. I shall elucidate the contact line motion where appropriate, and show comparisons to experiments where possible. These simulation results provide insights into the design principles of natural superhydrophobic surfaces, as well as into controlling multiphase flow in microfluidic devices. |
| Title: | Majorana Fermions in Semiconductor Nanowires |
| Speaker: | Professor Hongqi Xu |
| Date: | 4 January 2013 |
| Time: | 3pm - 4pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Xiong Qihua |
| Abstract: | The search for Majorana fermions is one of the most prominent fundamental research tasks in physics today. Majorana fermions are an elusive class of fermions that act as their own antiparticles. Although an extensive effort has been made worldwide in particle physics, Majorana fermions have so far not been convincingly discovered in free space. In this talk, I report on the realization and observation of Majorana fermions in topological superconducting nanowire quantum systems constructed using high crystalline-quality semiconductor InSb nanowires and superconductor Nb contacts. |
| Title: | Direct Polarity assignment in semiconductor nanowires from atomic resolution dumbbell analysis: influence in the growth mechanisms and electronic and optical properties |
| Speaker: | Professor Jordi Arbiol |
| Date: | 4 January 2013 |
| Time: | 1.30pm - 2.30pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Assistant Professor Xiong Qihua |
| Abstract: | The formation of atomic pairs with opposite partial charge due to the chemical bonding iconicity within a
semiconductor material has huge impact in many physical properties. Thus, it is worth to determine the
orientation of these atomic pairs, so called dumbbells, to determine the polarity of the structure. Polarity
influences the growth mechanism driving the formation of different architectures [1], and it is strongly
correlated with the electronic properties [2]. In this context, aberration-corrected Scanning Transmission
Electron Microscopy (STEM) [1,2] is the chosen technique for the direct dumbbell visualization and
hence, direct polarity assignment at atomic scale. We have defined a new guideline for the direct atomic
resolution polarity determination of semiconductor nanowires (NWs) from binary compounds in the case
where one of the atoms is extremely light (O or N: ZnO [2,3] and GaN/AlN [2,4]). The proposed
experimental via opens new routes for the fine characterization of nanostructures, where the polarity is
crucial for the understanding of their physical properties (optical and electronic) as well as their growth
mechanisms [3,4,5].
References [1] E Uccelli et al., Nano Letters 11, 3827 (2011) [2] M de la Mata et al., Nano Letters 12, 2579 (2012) [3] M I B Utama et al., Nano Letters, 12, 2146 (2012) [4] F Schuster et al., Nano Letters, 12, 2199 (2012) [5] M. I. B. Utama et al., Advanced Functional Materials, Early View, DOI:10.1002/adfm.201202027 (2012) |