Seminars 2014

Title:	Nanoscale Magnetic Tunnel Junction
Speaker:	Professor Hideo Ohno
Date:	18 December 2014
Time:	3pm - 4pm
Venue:	SPMS-LT4
Host:	Assistant Professor Lew Wen Siang
Abstract:	I review nanoscale magnetic tunnel junction technology and its application to nonvolatile VLSI [1]. First, I present physics and materials science of perpendicular CoFeB-MgO utilizing perpendicular magnetic anisotropy at the CoFeB-MgO interface [2, 3]. Next, I will discuss about three terminal devices utilizing current-induced domain wall motion [4]. Finally electric-field switching of magnetization of perpendicular CoFeB-MgO MTJs [5] will be presented. At the end, I will discuss about the future prospect of these technologies. [1] H. Ohno, International Electron Device Meeting (IEDM) (invited) 9.4.1 (2010). [2] S. Ikeda, et al. Nature Materials, 9, 721 (2010). [3] H. Sato, et al. IEDM 2013 and Appl. Phys. Lett. 105, 062403 (2014). [4] S. Fukami, et al. IEDM 2013 and Nature Comm. 4:2293 doi: 10.1038/ncomms3293 (2013). [5] S. Kanai, et al. Appl. Phys. Lett. 101, 122403 (2012); 103, 072408 (2013); 104, 212406 (2014)

Title:	Non-canonical DNA structures under molecular crowding conditions
Speaker:	Professor Daisuke Miyoshi
Date:	12 December 2014
Time:	11am - 12pm
Venue:	MAS Executive Classroom 2
Host:	Associate Professor Phan Anh Tuan
Abstract:	The canonical structure of DNA is the B-form duplex with Watson−Crick base pairs. However, some DNAs are prone to structural polymorphism, forming triplexes and quadruplexes with not only Watson−Crick but also non-Watson−Crick base pairs such as Hoogsteen base pairs. The structural polymorphism of nucleic acids, which can be specific and important signals in nucleic acid−nucleic acid, nucleic acid−protein, and nucleic acid−drug interactions, is influenced not only by their sequence but also by their surroundings. One of the most distinguishing features of the intracellular environment is the condition of being crowded with biomolecules, referred to as “molecular crowding”, in which the total amount of biomolecules in cells reaches up to 400 g/L, and the biomolecules occupy up to 40% of the cellular volume. We have studied how molecular crowding affects structure, stability, and function of nucleic acids and found that molecular crowding destabilizes the canonical duplex structure and stabilizes the non-canonical ones, such as triplex, quadruplex, and junction. Selected publications 1. Effects of Molecular Crowding on the Structures, Interactions, and Functions of Nucleic Acids, Chem. Rev., 114, 2733 (2014). 2. Drastic stabilization of parallel DNA hybridizations by a polylysine comb-type copolymer with hydrophilic graft chain, ChemMedChem, 9, 2156 (2014). 3. In Vitro Assays Predicting of Telomerase Inhibitory Effect of G-Quadruplex Ligands in Cell Nuclei, J. Phys. Chem. B, 118, 2605 (2014). 4. Sequence and Solvent Effects on Telomeric DNA Bimolecular G-Quadruplex Folding Kinetics, J. Phys. Chem. B, 117, 12391 (2013). 5. Multiple and cooperative binding of fluorescence light-up probe Thioflavin T with human telomere DNA G-quadruplex, Biochemistry, 52, 5620 (2013). 6. Thermodynamics - Hydration Relationships within Loops that Affect G-Quadruplexes under Molecular Crowding Conditions, J. Phys. Chem. B, 117, 963 (2013). 7. The beads-on-a-string structure of long telomeric DNAs under molecular crowding conditions, J. Am. Chem. Soc., 134, 20060 (2012). 8. Phthalocyanines: a new class of G-quadruplex-ligands with many potential applications, Chem. Commun., 48, 6203 (2012).

Title:	Shining Light on Atomically Thin Semiconducting Crystals
Speaker:	Mr Edbert Jarvis Sie
Date:	3 December 2014
Time:	2pm - 3pm
Venue:	MAS Executive Classroom 2
Host:	Associate Professor Sum Tze Chien
Abstract:	Atomically thin crystals have recently become available for investigation in basic science and development in future electronics. These include monolayers of MoS₂ and WS₂ , which are the thinnest ever discovered semiconducting crystals. Although they are merely three-atom thick and may appear simple in their crystal structures, they possess unusual properties not found in conventional semiconductors. In this seminar, we shall revisit their unique electronic properties, and focus on two novel aspects that we have recently discovered. First, this semiconducting crystal is so thin that it affects the essential physics on how the electrons would interact among each other. This allows a formation of excitonic quasiparticles including the “biexcitons” with extremely large binding energies. By using light, we created these biexcitons, and found that they are unusually stable at room temperature [1]. Second, this crystal has a unique electronic band structure because it has two different “valleys” with corresponding energy gaps that are normally locked in equal magnitude. In order to split their energies, we must break time-reversal symmetry, and we did this using light! We further propose that by shining light we can turn this atomically thin semiconductor into a new quantum state of matter, the so-called “chiral Floquet” topological insulator [2]. [1] E. J. Sie et al., “Biexciton formation and many-body effects in monolayer MoS₂ ”, arXiv:1312.2918. [2] E. J. Sie et al., “Valley-selective optical Stark effect in monolayer WS₂ ”, Nature Materials, arXiv:1407.1825.

Title:	Localized Structures, Optical Vortices and Extreme Events in Laser Dynamics
Speaker:	Professor J. R. Tredicce
Date:	20 November 2014
Time:	4pm to 5pm
Venue:	Hilbert Space
Host:	Associate Professor David Wilkowski
Abstract:	During the last years we have been studying different optical phenomena in laser systems, like the formation of localised structures (also called cavity solitons), the spontaneous generation of optical vortices, or the probability of observing extreme events (also called optical rogue waves). The objective of this talk is to discuss the origin of each of the above mentioned phenomena in optics from the point of view of general nonlinear dynamics theory. We present experimental and theoretical results obtained in different optical systems and in particular we will discuss lasers with optical injection and laser with saturable absorbers where those phenomena have been recently observed. The comparison between the obtained experimental and theoretical results allow us to retrace the common necessary conditions to observe cavity solitons, spontaneous formation of vortices and appearance of extreme events in a given nonlinear system. Finally we will show that the so called external crisis of deterministic chaotic attractors may be able to generate optical rogue waves.

Title:	All-optical, three-dimensional electron pulse compression
Speaker:	Dr Wong Liang Jie
Date:	13 November 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Assistant Professor Chong Yidong
Abstract:	The ability of ultrafast electron diffraction (UED) to probe structural dynamics with atomic spatiotemporal resolution has fueled a wealth of exciting research on the frontiers of physics, chemistry, biology and materials science. To focus the moving electron pulse and achieve the ultrashort pulse durations required, most UED setups currently employ static field elements, which have disadvantages in the form of electron pulse distortion by magnetic lenses, and the necessity to remove magnetic fields from the sample and the cathode. In this talk, I will present a three-dimensional electron pulse compression scheme that uses only optical pulses. The scheme comprises a succession of Hermite-Gaussian optical modes that effectively fashions a three-dimensional optical trap in the electron pulse's rest frame. I will discuss theoretical and numerical results demonstrating the critical role of the optical incidence angle, and showing that compression in each Cartesian dimension can be controlled without affecting electron pulse properties in orthogonal dimensions, at the lowest order. Broader applications of the mechanism studied potentially include compressing or focusing accelerated protons and neutral atoms, and enhancing the quantum degeneracy of electron packets.

Title:	Time-resolved laser-induced Faraday effect in EuO
Speaker:	Dr Takayuki Makino
Date:	7 November 2014
Time:	11am - 12pm
Venue:	MAS Executive Classroom 1
Host:	Associate Professor Sun Handong
Abstract:	The laser-induced ultrafast spin dynamics have been investigated by time-resolved pump-probe and Faraday rotation spectroscopies in ferromagnetic EuO thin films. We demonstrate that the laser beam can enhance the magnetization on an ultrafast time scale. The decays time for the magnetization enhancement is about 1 nanosecond. In its temperature dependence, there is a maximum slightly below the Curie temperature associated with this dynamical enhancement of magnetization. It also dominates the demagnetization counterpart at 55 K. It is attributed that this transient collective ordering to the enhancement of the f-d exchange interaction as a result of photoexcitation. We also observed that the circularly polarized light can control the magnetization precession at 10 K. This takes place within the 100-fs duration of a single laser pulse, through combined contribution from two nonthermal photomagnetic effects, i.e., enhancement of the magnetization and an inverse Faraday effect. From the magnetic field dependencies of the frequency and the damping parameter, the intrinsic Gilbert damping coefficient was also evaluated.

Title:	Coherent Control in Metamaterials for Device and System Applications
Speaker:	Dr Kevin F. MacDonald
Date:	5 November 2014
Time:	4pm – 5pm
Venue:	MAS Executive Classroom 2
Host:	Assistant Professor Cesare Soci
Abstract:	Harnessing the coherent interaction of optical waves on photonic metamaterial nanostructures provides for ultrafast all-optical control, at arbitrarily low intensity, of a wide variety of optical phenomena, from absorption and refraction to optical activity and anisotropy. This presentation introduces the coherent control concept and explores device and systems application potential in spectroscopy and all-optical data processing through a number of experimental demonstrations.

Title:	Measuring heat in a quantum process
Speaker:	Dr Kavan Modi
Date:	16 October 2014
Time:	3pm - 4pm
Venue:	Hilbert Space
Host:	Assistant Professor Tomasz Paterek
Abstract:	Accurately describing work extraction is a central objective of thermodynamics. Therefore measuring work, heat, and temperature are the essential to the theory of thermodynamics. However, In order to measure the work done on a system or heat exchange with a bath, one has to know the state of the system and the Hamiltonian throughout the process. This is typically not possible for a quantum process. The concepts of work and heat are surprisingly subtle when generalizations are made to arbitrary quantum processes. We use schemes to measure work distribution, recently developed in [PRLs 110, 230601 and 230602 (2013)], to measure heat distribution for discrete quantum processes, described by completely-positive trace preserving maps. Our scheme should pave the way for experimental explorations of the Landauer principle and hence the intricate energy to information conversion in mesoscopic quantum systems. References: Phys. Rev. E 90, 020101(R), arXiv:1402.4499, arXiv:1406.2801

Title:	Quantum state discrimination by LOCC
Speaker:	Dr Somshubhro Bandyopadhyay
Date:	9 October 2014
Time:	3pm - 4pm
Venue:	Hilbert Space
Host:	Assistant Professor Tomasz Paterek
Abstract:	Suppose a composite quantum system is known to be in one of many states, not necessarily orthogonal, such that its parts are distributed among spatially separated observers. The goal is to learn about the state of the system using only local quantum operations and classical communication between the parties (LOCC). This problem, known as local state discrimination, is of considerable interest, as in many instances the information obtainable by LOCC is strictly less than that achieved with global measurements even when the states are mutually orthogonal. Thus the problem of local state discrimination serves to explore fundamental questions related to local access of global information and the relationship between entanglement and local distinguishability. In this talk I will present a self contained review of local state discrimination along with some recent results.

Title:	Toward a universality between various classes of unconventional superconductors
Speaker:	Dr Tanmoy Das
Date:	7 October 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Professor Christos Panagopoulos
Abstract:	Unconventional superconductivity has been observed in a growing class of materials that appear neither identical to the conventional superconductors of electron-lattice coupling origin, nor related to each other. Despite more than three decades of research and several candidate proposals, a concluding and unified, if any, mechanism for the electron pairing in these families has not prevailed. In this talk, I will present a comprehensive analysis of the superconducting phase of more than 25 different materials belonging to various families within the copper-oxides, heavy-fermions, organics, and the recently discovered ironpnictides, iron-chalcogenides, and oxybismuthides. We demonstrated that when multiple tuning (e.g., pressure on doped samples etc.) is employed, several new and uncharted insights related to the superconducting properties and their ‘parent’ normal state properties are revealed. Our findings include a universal two superconducting (SC) dome–like feature in all materials studied here. The dome near the quantum critical point, if exists, usually has a lower transition temperature (Tc), while the second SC dome appearing around a non-Fermi liquid (NFL) background has higher Tc. I will conclude with establishing universality and extracting common parameters across all these materials, and thereby proposing a generic route to higher-Tc superconductivity. Reference: T. D. and Christos Panagopoulos, under review.

Title:	Advances in the Design of UHV Components and Manipulation used in Materials Research
Speaker:	Dr Peter Tuatara
Date:	24 September 2014
Time:	3pm - 4.30pm
Venue:	MAS Executive Classroom 1
Host:	Dr Alexander Petrovic
Abstract:	UHV Design specialises in the design, manufacture and supply of high precision instruments used in the high and ultra-high vacuum markets for materials research. The product portfolio consists of high-performance motion devices including magnetically coupled rotary drives, linear and XYZ translators; Sample transfer solutions; Multi-axis cryogenic manipulation and high-uniformity heating stages. All products are assembled in clean room conditions to virtually eliminate the chance of contamination and follow stringent quality control methods to ensure the ultimate in quality and reliability. Products are sold and supported globally via an extensive distribution network to the R&D sector including universities and government laboratories; OEMs (vacuum system integrators) and to the Semiconductor and Industrial markets. Applications include Deposition and a vast array of Surface Analysis techniques.

Title:	Narrowband source of photon pairs for efficient interaction with single atoms
Speaker:	Mrs. Gurpreet Kaur Gulati
Date:	22 September 2014
Time:	2pm - 3pm
Venue:	Hilbert Space
Host:	Assistant Professor Lan Shau-Yu
Abstract:	We report an efficient source of narrowband, time correlated photon pairs from a cold cloud Rb atoms via four-wave mixing process using a cascade level scheme. The heralded photons show anti-bunching with g^2(0) < 0. 03, indicating a high single photon fidelity. In an optical homodyne measurement we directly measure the temporal envelope of these photons inherited from the cascade decay. We observe an exponential decay for the idler photon (heralded on the signal) and counterintuitively, an exponential rise for the signal photon (heralded on the idler). Furthermore, we show that by inverting the temporal profile of the herald photons with an asymmetric cavity, we obtain single photons of the desired wavelength and rising exponential temporal profile, ideal for efficient interaction with a single 87 Rb atom. At the same time, our experiment illustrates the breakdown of a realistic interpretation of the heralding process in terms of defining an initial condition of a physical system.

Title:	Novel semiconductor materials and nanostructures grown by MBE for optoelectronic applications
Speaker:	Dr Qian-Dong ZHUANG
Date:	29 August 2014
Time:	3pm - 4pm
Venue:	Hilbert Space
Host:	Associate Professor Sun Handong
Abstract:	Nanostructured semiconductor materials have attracted increasing attention in the last decade due to their unique functionalities and the promising potential as new building blocks for next generation devices. Of particular interest is the III-V compound semiconductor nanostructures such as quantum dots, nanowires and their integration with Si platform or newly emerged 2D materials. This talk will present our recent research outcomes on several novel semiconductor nanostructures, from quantum dots synthesised by novel epitaxial techniques to narrow bandgap nanowires and hybrid material systems. Fundamental properties and device applications in lasers, LEDs, photodetectors and quantum technology will be discussed.

Title:	The quest for the unitary Bose gas
Speaker:	Professor Frederic Chevy
Date:	26 August 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Associate Professor David Wilkowski
Abstract:	The study of strongly interacting ultracold Fermi gases have revealed the surprising universal scaling properties of ensembles of fermions at the unitary limit where the scattering length is infinite. The question of the existence of a similar universal unitary Bose gas is still open, partly because such a system suffers from strong inelastic losses at unitarity. In this talk I will report on the recent progress on the hunt for this hypothetical universal system. I will show how thermodynamics measurement have captured quantitatively the corrections to the mean-field approximation close to a Feshbach resonance. I will also demonstrate that a unitary Bose gas can be stabilized at high temperature thanks the suppression of inelastic losses at high temperature. Finally I will discuss the effect of the competition between elastic and inelastic processes in momentum distribution measurements performed at JILA.

Title:	Fano interference and a slight fluctuation of the Majorana hallmark
Speaker:	Prof. Dr. Antonio C. Seridonio
Date:	21 August 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Assistant Professor Pinaki Sengupta
Abstract:	According to the Phys. Rev. B 84, 201308(R) (2011), an isolated Majorana state bound to one edge of a long enough Kitaev chain in the topological phase and connected to a quantum dot, results in a robust transmittance of 1/2 at zero-bias. In this talk, I will show that the removal of such a hallmark can be achieved by using a metallic surface hosting two adatoms in a scenario where there is a lack of symmetry in the Fano effect, which is feasible by coupling the Kitaev chain to one of these adatoms. Thus in order to detect this feature experimentally, one should apply the following two-stage procedure: (i) first, attached to the adatoms, one has to lock AFM tips in opposite gate voltages (symmetric detuning of the levels) and measure by an STM tip, the zero-bias conductance; (ii) thereafter, the measurement of the conductance is repeated with the gates swapped. For the detuning away from the Fermi energy and in the case of strong coupling tip-host, this approach reveals in the transmittance, a persistent dip placed at zero-bias and immune to the aforementioned permutation, but characterized by an amplitude that fluctuates slightly around 1/2. However, in the case of a tip acting as a probe, the adatom decoupled from the Kitaev chain becomes completely inert and no fluctuation is observed. Therefore, the STM tip must be considered in the same footing as the ``host+adatoms'' system. As a result, I will discuss that despite the small difference between these two Majorana dips, the zero-bias transmittance as a function of the symmetric detuning yields two distinct behaviors, in which one of them is unpredictable by the standard Fano's theory. Therefore, to access such a non trivial pattern of Fano interference, the hypothesis of the STM tip acting as a probe should be discarded [1]. 1. SERIDONIO, A. C. ; SIQUEIRA, E. C. ; DESSOTTI, F. A. ; MACHADO, R. S. ; YOSHIDA, M. Journal of Applied Physics, v. 115, p. 063706, 2014.

Title:	Slow Dynamics and Narrow Lines by means of Long- lived states and Coherences
Speaker:	Dr Riddhiman Sarkar
Date:	19 August 2014
Time:	3pm - 4pm
Venue:	Hilbert Space
Host:	Associate Professor Phan Anh Tuan
Abstract:	Dynamic processes in solution NMR spectroscopy can be probed provided the nuclear relaxation rate constant does not exceed the rate constant of the process. Phenomena occurring on a time scale longer than the spin-lattice relaxation time constant, T1 , were not amenable to study by conventional NMR before the discovery of long-lived singlet states. However, using Long-lived nuclear spin states (LLS) and coherences (LLCs), one can probe dynamic processes that were beyond the scope using methods based on T1 s and T2 s. LLS experiments can be performed either in zero or in high magnetic fields for scalar coupled spin pairs. We developed methods for exciting and preserving LLS in high fields for a wide class of molecules. Slow diffusion has been measured for a mixture of molecules having different NMR parameters using LLS. LLS have been observed in highly mobile parts (Gly-75 and 76) of Ubiquitin. Dynamic Nuclear Polarization (DNP) is one of the methods to overcome the inherent low sensitivity of NMR spectroscopy. We have conceived an experiment to preserve DNP enhanced magnetization by conversion into LLS. A way of improving resolution and sensitivity of NMR has been designed by creation of long-lived coherences (LLC) in biomolecules.

Title:	Asymmetric whispering gallery microcavity optics and photonics
Speaker:	Professor Xiao Yunfeng
Date:	19 August 2014
Time:	11am - 12pm
Venue:	Hilbert Space
Host:	Associate Professor Sun Handong
Abstract:	Confinement and manipulation of photons using microcavities have triggered intense research interest in both basic and applied physics for more than one decade. Prominent examples are whispering gallery microcavities which confine photons by means of continuous total internal reflection along a curved and smooth surface. The long photon lifetime, strong field confinement, and in-plane emission characteristics make them promising candidates for enhancing light-matter interactions on a chip. In this talk, we report experimentally a new type of on-chip whispering gallery microcavity which supported both highly unidirectional emission and ultra-high-Q factors exceeding 100 million in near infrared. By doping erbium, the unidirectional-emission lasing was observed in 1,550 nm band with the threshold as low as 2 microwatts. Moreover, we propose a sensing mechanism by monitoring mode broadening in microcavities, which is immune to both noise from the probe laser and environmental disturbances, and would remove the strict requirement for ultra-high-Q mode cavities for sensitive nanoparticle detection.

Title:	Towards Quantum-Safe Cryptography
Speaker:	Professor Michele Mosca
Date:	18 August 2014
Time:	10.30am - 11.30am
Venue:	MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:	Assistant Professor Chew Lock Yue
Abstract:	Cryptographic tools, such as key establishment and signatures, are a fundamental part of the information security infrastructure. Quantum computers will eventually break most of the currently deployed publickey signature and key establishment tools. Are we ready? It is critical that robust implementations of quantum-safe alternatives to these tools are deployed before quantum computers break them. I will discuss the risk of this catastrophic event, the potential solutions, and the path to quantum-proofing the cryptographic infrastructure.

Title:	Pulse designed nonlinear Kerr devices for quantum technologies
Speaker:	Prof. Dr. Gagik Yu. Kryuchkyan
Date:	15 August 2014
Time:	3pm – 4pm
Venue:	Hilbert Space (SPMS-PAP-02-02)
Host:	Assistant Professor Chew Lock Yue
Abstract:	The Kerr nonlinearity leading to photon-photon interaction is a well known phenomenon in nonlinear optics and quantum technologies. It has widely used from designing of ultra-fast pulses to elaboration of quantum gates. In this report, we discuss nonlinear Kerr resonators driven by train of electromagnetic pulses that are operated at level of few-photon level. This regime is realized for strong Kerr-nonlinearity exceeding dissipation rates. These devices are realized in several physical systems including atoms inserted in a cavity, nanomechanical oscillators and a superconducting cavity with nonlinear Josephson junction. More importantly, the Kerr-type systems can be controlled by the sequence of tailored pulses that leads to obtaining of pulse designed new qualitatively quantum effects. This report includes description of these effects in phenomena of multi-photon blockade, observation of bistability and chaos at few-photons level and in production of Fock states.

Title:	Photonic topological insulators and pseudomagnetism
Speaker:	Dr Mikael Rechtsman
Date:	7 July 2014
Time:	4pm - 5pm
Venue:	Hilbert Space (SPMS-PAP-02-02)
Host:	Assistant Professor Chong Yidong
Abstract:	I will present two examples in which ‘fictitious fields’ lead to surprising photonic effects that would be difficult (if not impossible) to achieve with real fields. Firstly, I will present the first observation of the topological protection of light - a ‘Photonic Floquet Topological Insulator’ [1]. The structure is an array of coupled helical waveguides (the helicity generates a fictitious circularly-polarized electric field that leads to the TI behavior). Second, I will demonstrate artificial magnetic fields (‘pseudomagnetism’) in photonic lattices [2]. The pseudomagnetic field is generated by inhomogeneously straining the system (thus breaking periodicity), and leads to photonic Landau levels with very high photonic density of states. Potential applications include robust photonic devices and strong light-matter interaction over large areas. [1] Rechtsman, M. C. et al. Nature 496, 196–200 (2013). [2] Rechtsman, M. C. et al. Nature Photon. 7, 153–158 (2013).

Title:	Tuning Spin-Orbit Interaction and 1D Thermoelectric Transport in InAs Nanowires
Speaker:	Professor Xuan Gao
Date:	27 June 2014
Time:	11am - 12pm
Venue:	Hilbert Space (SPMS-PAP-02-02)
Host:	Associate Professor Xiong Qihua
Abstract:	InAs nanowires provide an interesting platform for spintronic device and thermoelectric energy conversion applications, owing to their strong quantum confinement and spin orbit interaction (SOI) effects. In the first part of this talk, we will discuss our recent results of gate enabled generation and control of the Rashba SOI in InAs nanowires, which is essential for the realization of many spintronic devices. Second, we present a study of the thermoelectric properties of InAs nanowires where the gate was used to control the electrons' Fermi level. At temperatures below about 100K, oscillations in the thermopower and power factor due to the formation of one-dimensional (1D) electron sub-bands are observed in semiconductor nanowires for the first time. We also discuss the limiting factors in the pursuit of 1D confinement enhanced thermoelectric performance in semiconductors.

Title:	Majorana mode in the vortex core and single-layer FeSe on SrTiO₃ with a superconducting T_c above 100 K
Speaker:	Professor Jin-Feng Jia
Date:	26 June 2014
Time:	4pm - 5pm
Venue:	Hilbert Space (SPMS-PAP-02-02)
Host:	Associate Professor Xiong Qihua
Abstract:	In the first part, I will talk about our efforts to identify Majorana fermions in the vortex core of superconducting topological insulators. We systematically investigated the spatial profile of the Majorana mode and the bound quasiparticle states within a vortex in Bi₂Te₃ /NbSe₂ . While the zero bias peak in local conductance splits right off the vortex center in conventional superconductors, it splits off at a finite distance ~20nm away from the vortex center in Bi₂Te₃ /NbSe₂ , primarily due to the Majorana fermion zero mode. While the Majorana mode is destroyed by reducing the distance between vortices, the zero bias peak splits as a conventional superconductor again. This work provides strong evidences of Majorana fermions and also suggests a possible route to manipulating them. In the second part, I will talk about a direct transport measurement of high Tc superconductivity in the FeSe/STO system. By in situ 4-point probe technique that can be conducted at an arbitrary position of the single-layer FeSe films on STO, we detected superconductivity transition at a temperature above 100 K.

Title:	Battling the loss in plasmonics and Metamaterials
Speaker:	Professor Jacob B. Khurgin
Date:	19 May 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Associate Professor Xiong Qihua
Abstract:	Recent years have seen staggering growth of interest in using nanostructured metals in optical range with the goal of enhancing linear and nonlinear optical properties or even engineering novel optical properties unknown in Nature – usually this burgeoning field is referred to as “Plasmonics and Metamaterials”. After the initial years of excitement the community is belatedly beginning to recognize that loss in the metal is an important factor that might impede practical application of plasmonic devices, be it in signal processing, sensing, imaging or more esoteric applications like cloaking. Yet there is still an optimism that the loss can be either cleverly “designed away”, compensated by gain, or a new lossless materials can be found. In this talk we examine these concepts one by one. First, based entirely on energy-conservation considerations, we explain why subwavelength confinement requires metal or another material with negative permittivity. We demonstrate that in truly sub-wavelength metal structures the metal loss is inherent and cannot be engineered away by crafty changes in shape. Then we show that when it comes to enhancing the device performance (solar cells, sensors, nonlinear optical devices, etc.) only the most inefficient devices can be improved by plasmonics while the performance of any decent device will only degrade. Then we consider idea of compensating loss using semiconductor gain medium and demonstrate that required gain can never be achieved due to increase in recombination rates caused by Purcell effect. After that we consider the physics of losses in metals at optical frequencies and show that the nature of these losses is quite different from the losses in RF domain. We then show that negative dielectric constant at optical frequencies does not have to inevitably lead to large absorption, and guardedly point to the tentative way in which new materials with negative dielectric constant and very low loss might be synthesized, thus restoring the faint hope for plasmonics.

Title:	Wide bandgap semiconductors for Nanophotonics
Speaker:	Dr Igor Aharonovich
Date:	19 May 2014
Time:	11am -12pm
Venue:	Hilbert Space
Host:	Associate Professor Fan Hongjin
Abstract:	Optical microcavities are important components in studying solid state cavity quantum electrodynamics and developing novel devices such as low threshold lasers, single photon sources and ultra-sensitive sensors. Wide bandgap semiconductors are particularly interesting in this respect due their ability to host bright emitters in the whole spectral range – from ultraviolet to the infra-red. In the first part of my talk, I will discuss fabrication methods of optical resonators out of gallium nitride containing InGaN quantum dots (QDs). Quality factors as high as ~ 10,000 were measured from the microdisk cavities and low threshold lasing was achieved. Furthermore, we developed a dynamical tuning of the whispering gallery modes of the microdisk cavities based on a selective, in situ photo-enhanced process. Such tuning is essential to demonstrate efficient coupling interaction between the cavity mode and the emitter. I will then discuss diamond as an emerging platform for room temperature quantum information processing. In particular, I will describe our efforts to incorporate novel ultra - bright emitters into practical photonic structures and devices – sculpted out of a single crystal diamond. A special attention will be devoted to the homoepitaxial regrowth process of thin diamond membranes that served as building blocks for optical cavities with quality factors of ~ 3000. Finally, I will briefly discuss a completely novel approach to engineer optical cavities out of SiC – one of the most promising materials for modern optoelectronic devices. Realization of optical cavities out of wide bandgap semiconductors is a pivotal step towards integrated nanophotonic networks with improved functionalities and a better understanding of light- matter interactions at the nanoscale.

Title:	NEXT GENERATION CROSSTALK ELIMINATED SCANNING PROBE MICROSCOPE AND ADVANCED APPLICATIONS FOR CUTTING-EDGE RESEARCH
Speaker:	Dr Sang-Joon Cho
Date:	25 April 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Assistant Professor Lew Wen Siang
Abstract:	In recent years, a key achievement in the AFM industry has been the elimination of cross-talk during XY scanning. Specifically, the XY flexure scanner is decoupled from the Z scanner to which the probe is attached. Building upon the strength of the crosstalk eliminated (XE) platform, a remarkable capability for non-contact AFM in ambient conditions is achieved by adopting a high-speed Z scanner actuated by dedicated high force piezostacks. The design concept of the XE AFM provides an open platform for developing other scanning probe microscope techniques such as Tip-enhanced Raman Spectroscopy and Scanning Ion Conductance Microscopy (SICM) in addition to the many SPM offspring. The one of the offspring is a Magnetic Force Microscopy (MFM) – the first scanning probe technique and turned out to be a powerful tool for submicron-scale magnetic image mapping. In order to measure the magnetic properties of periodic structures based on magnetic/nonmagnetic films, the MFM technique is better suited that possess the high sensitivity required to monitor magnetic domain structure in thin films and very small elements of different shapes. In order to meet the specifications needed by researchers and industry, we developed the system with lower detector noise and concomitantly higher resolution imaging, lower drift with temperature control for image distortion and dual servo x-y scan for greater accuracy. We will discuss the applications of MFM and its current enhancement.

Title:	Excitons versus free charges: a photophysical picture of organo-lead tri-halide perovskites for highly efficient hybrid solar cells
Speaker:	Dr Annamaria Petrozza
Date:	16 April 2014
Time:	11am - 12pm
Venue:	MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:	Assistant Professor Cesare Soci
Abstract:	Hybrid perovskite solar cells were first introduced in a dye-sensitized configuration, where the dye was replaced by perovskite crystals sensitizing the surface of mesoprorous TiO2 . In the perovskite-sensitized configuration, developed within the excitonic solar cell concept, there is no requirement for long range exciton or charge diffusion, since the perovskite crystals are sandwiched within a nanoscale heterojunction between an electron accepting metal oxide TiO2 and a hole-accepting organic hole-transporter (or redox active electrolyte) and long range transport occurs in those phases. Whilst the rapid advancement of this sensitized approach has occurred, there has been in parallel a striking divergence in technology, where the mesoporous TiO2 has been proven nonessential, and simply a solid absorber layer sandwiched within a planar heterojunction has been demonstrated to operate extremely well, with power conversion efficiencies of over 15% already reported. Here, first we report that the photo-excitations diffusion lengths are >1 micrometer in the mixed halide perovskite, an order of magnitude greater than the absorption depth. By contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells, and identify a critical parameter to optimize for future perovskite absorber development. The fundamental question left open in the study concerns the nature of the elementary photo-excitations that are involved in the photovoltaic mechanisms: in particular whether bound excitons are created and transport energy to the heterojunction, or free charges are spontaneously generated within the bulk of the perovskite. We find that at equilibrium, following photoexcitation, there is a predominant fraction, near unity, of free charges in the photovoltaic (PV) operating regime.

Title:	Photo-excitation mechanism and application of the bio-organic interface
Speaker:	Professor Guglielmo Lanzani
Date:	15 April 2014
Time:	11am - 12pm
Venue:	MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:	Assistant Professor Cesare Soci
Abstract:	The possibility to excite a living cell through a controlled stimulus offers a wealth of applications in neuroscience and medicine, for healing, studying and diagnostic. There are several techniques that have been proposed and tested, mainly based onto two different actions: by electrical stimulation and by light stimulation. The latter has a number of advantages, being less invasive, better confined, more selective. We propose here a new approach, based on light absorbing polymer layers in contact with the cell. First experiment in primary hippocampal neurons in vitro validated the approach, showing that a short light pulse can elicit an action potential. This prompted further investigations and the recent demonstration of light excitation in explanted blind retinas. A parallel study was carried out on HEK line cells, as simpler model for the bio/ organic, natural/artificial interface. This study shows that light absorption in the polymer causes a local heating at the polymer surface that induces a temperature change in the cell membrane. Electrical parameter of the cell, conductance and capacity, are changed by the temperature gradient and result into a modification of the cell membrane potential. This mechanism is fully characterized and quantitatively reproduced by a simple equivalent circuit model.

Title:	Quantum simulations of Mott transitions and interacting relativistic theories with photons
Speaker:	Dr Dimitris G. Angelakis
Date:	3 April 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Associate Professor David Wilkowski
Abstract:	I will start by briefly reviewing our early works for observing photon-blockade induced Mott transitions in coupled cavity QED systems [1]. After briefly touching on the idea of simulating spin-models and the Fractional Hall effect [2], I will review more recent developments in realizing continuous strongly correlated classical and relativistic models (Luttinger and Thirring) in quantum nonlinear EIT media [3,4]. I will conclude by presenting our ongoing efforts for simulations of out of equilibrium phenomena in driven resonator arrays and discuss possible implementations slow light and circuit QED set ups[5,6,7]. [1] D.G. Angelakis, M.F. Santos and S. Bose, Phys. Rev. A 76, 031805(R) (2007). [2] J. Cho, D.G. Angelakis, Phys. Rev. Lett 101, 246809 (2008). [3] D.G. Angelakis, M.-X. Huo, E. Kyoseva and L.C. Kwek, Phys. Rev. Lett. 106, 153601 (2011). [4] D.G. Angelakis, M.-X. Huo, D. E. Chang, LC Kwek, V,. Korepin. Phys. Rev. Lett. 110, 100502 (2013). [5] T. Gruzic, S. R. Clark, D. G. Angelakis. Dieter Jacksh, New Jour,. of Phys. 14, 103025 (2012). [6] T. Gruzic, S. R. Clark, Dieter Jacksh, D. G. Angelakis. Phys. Rev. A. 87 053846 (2013). [7] N. Schetakis, T. Gruzic, S. R. Clark, Dieter Jacksh, D. G. Angelakis. J. Phys. B: At. Mol. Opt. Phys. 46 (2013) 224025

Title:	When disorder is just right: A lecture on complexity-driven photonics
Speaker:	Professor Andrea Fratalocchi
Date:	31 March 2014
Time:	2pm - 3pm
Venue:	MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:	Assistant Professor Cesare Soci
Abstract:	Disorder and chaos are ubiquitous expressions of nature that are mostly unwanted in applications, as they introduce unpredictability and make difficult to explain experimental results. On the contrary, if properly understood, they can be the basis on a completely new technology that is sustainable, scalable and extremely cheap. In this talk I will summarize my research in this field, discussing about the recent results of my group in the field of chaotic energy harvesting, light condensation effects and ultrafast subwavelength rogue waves.

Title:	Quantum Random Access Codes with Shared Randomness
Speaker:	Dr Laura Mancinska
Date:	27 March 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:	Dr Tomasz Paterek
Abstract:	We consider a communication method, where the sender encodes n classical bits into 1 qubit and sends it to the receiver who performs a certain measurement depending on which of the initial bits must be recovered. This procedure is called (n,1,p) quantum random access code (QRAC) where p > 1/2 is its success probability. It is known that (2,1,0.85) and (3,1,0.79) QRACs (with no classical counterparts) exist and that (4,1,p) QRAC with p > 1/2 is not possible. We extend this model with shared randomness (SR) that is accessible to both parties. Then (n,1,p) QRAC with SR and p > 1/2 exists for any n > 0. We give an upper bound on its success probability (the known (2,1,0.85) and (3,1,0.79) QRACs match this upper bound). We discuss some particular constructions for several small values of n. We also study the classical counterpart of this model where n bits are encoded into 1 bit instead of 1 qubit and SR is used. We give an optimal construction for such codes and find their success probability exactly -- it is less than in the quantum case. (This is joint work with Andris Ambainis, Debbie Leung and Maris Ozols.)

Title:	Floating on Air
Speaker:	Professor Detlef Lohse
Date:	24 March 2014
Time:	4pm - 5pm
Venue:	Hilbert Space (SPMS-PAP-02-02)
Host:	Associate Professor Claus-Dieter Ohl
Abstract:	A drop impacting on a solid surface deforms before the liquid makes contact with the surface. We directly measure the time evolution of the air layer profile under the droplet using high-speed color interferometry, obtaining the air layer thickness before and during the wetting process and the volume of the entrained droplet. This volume shows a Maximum as function of the impact velocity. We physically explain this maximum as a balance between capillary and inertial effects. The experiments are complemented by numerical simulations, based on potential flow for the impacting droplet and a lubrication theory for the gas layer in between the droplet and the surface, and by scaling laws which we derived analytically. The work is then extended in various directions: For the drop impact on a hot surface heated above the liquid’s boiling point, the droplet either immediately boils when it contacts the surface (‘‘contact boiling’’), or without any surface contact forms a Leidenfrost vapor layer towards the hot surface and bounces back (‘‘gentle film boiling’’), or both forms the Leidenfrost layer and ejects tiny droplets upward (‘‘spraying film boiling’’). We also look at the maximum spreading of impacting droplets on such heated surfaces, which is much further than for the impact on non-heated surfaces and shows universal scaling behavior. We also explain under what conditions splashing is achieved and connect it to the vapor and gas flow under the droplet. In the lecture we will not only show the (beautiful!) phenomena with high-speed visualisations and account for them theoretically, but we will also address various applications of our research in the industrial context.

Title:	Distinguishing the Indistinguishable
Speaker:	Gonzalo de la Torre
Date:	20 March 2014
Time:	3pm - 4pm
Venue:	Hilbert Space
Host:	Assistant Professor Tomasz Paterek
Abstract:	Quantum mechanics textbooks introduce mixed states highlighting that there is an intrinsic ambiguity in their preparation. That is, given a mixed state compatible with two physically different ensemble preparations, an experimenter has no means to distinguish which one was used to produce the said mixed state. We show here that this is only true if the mixture was performed using non-computable resources. Specifically, we introduce a protocol capable of distinguishing two different ensemble preparations in finite time and with arbitrarily high success probability provided that the mixture was performed in a computable way. Consequently, if classical physics is computable -as the Church-Turing thesis advocates- the only systems properly described by mixed states are those forming part of a bigger quantum system in a pure state.

Title:	Simulating the Universe with a Deck of Cards: an Exploration of the Scientific Method
Speaker:	Professor David M. Harrison
Date:	13 March 2014
Time:	4pm to 5pm
Venue:	Hilbert Space
Host:	Dr Ho Shen Yong
Abstract:	In this workshop we will simulate the universe with a (possibly) stacked deck of playing cards. We will draw cards one at time for the deck. The deck , in common with the universe, may have some patterns or organising principles that determine the order in which the data (the cards) appear. We will attempt to determine what if any principles are true for the deck of cards. This will turn out to allow us to have a surprisingly accurate discussion of what the scientific method can do and, perhaps more importantly, what the scientific method cannot do. The activity that we will be doing is suitable for students at a variety of levels, and has also proved effective with science teachers also at a variety of levels.

Title:	Heterostructured III-V nanowires grown on Si and graphene for photonic applications
Speaker:	Professor Helge Weman
Date:	12 March 2014
Time:	3pm - 4pm
Venue:	Hilbert Space
Host:	Associate Professor Xiong Qihua
Abstract:	Heterostructured semiconductor nanowires have attracted considerable attention in recent years because of their potential in future nano-electronic and nano-photonic device applications. In my talk I will report our recent results on the MBE growth as well as structural, optical and electrical properties of heterostructured III-V nanowires with a special emphasis on nanowire solar cell devices [1-4]. I will also describe on our recent work on epitaxial growth of GaAs nanowires on graphene [5,6], which is now being further developed by the spin-off company CrayoNano (crayonano.com). Epitaxial growth of semiconductor nanowires on graphene is an important scientific breakthrough since earlier attempts to grow semiconductor thin films, like Si and GaAs, on graphitic substrates have not been successful. It is also very appealing for device applications since graphene can function not only as a replacement of the expensive semiconductor substrate but also as a transparent and flexible electrode for e.g. nanowire based solar cells and LEDs. 1. L. Ahtapodov, J. Todorovic, T. Mjåland, P. Slåttnes, D.L. Dheeraj, A.T.J. van Helvoort, B.O. Fimland, and H. Weman, Nano Letters 12, 6090 (2012). 2. D.C. Kim, D.L. Dheeraj, B.O. Fimland, and H. Weman, Appl. Phys. Lett. 102, 142107 (2013). 3. A. M. Munshi, D.L. Dheeraj, J. Todorovic, A.T.J. van Helvoort, H. Weman, and B.O. Fimland, J. Cryst. Growth 372, 263 (2013). 4. A. M. Munshi, D. L. Dheeraj,V. T. Fauske, D. C. Kim, J. Huh, J. F. Reinertsen, L. Ahtapodov,K. D. Lee, B. Heidari,A. T. J. van Helvoort, B. O. Fimland, and H. Weman, Nano Letters, 14, 960 (2014). 5. M.A. Munshi, D.L. Dheeraj, V.T. Fauske, D.C. Kim, A.T.J. van Helvoort, B.O. Fimland, and H. Weman, Nano Letters 12, 4570 (2012). 6. A.M. Munshi and H. Weman, Phys. Status Solidi RRL 7, 713 (2013).

Title:	Development of microstructures for terahertz waves
Speaker:	Dr Withayachumnankul
Date:	27 February 2014
Time:	10.30am - 11.30am
Venue:	Hilbert Space
Host:	Assistant Professor Ranjan Singh
Abstract:	Terahertz radiation has become an important research area in the field of electromagnetics. Known as the ‘terahertz gap’, the radiation in this 0.1 to 10 THz frequency range was initially difficult to access with conventional electronic or photonic techniques. Advents of unconventional techniques have made possible terahertz emitters and detectors with a size of a pinhead. Achieving practical applications requires novel components to manipulate terahertz waves. For this purpose, microstructures become necessary to construct terahertz components whose properties are not available from natural materials. This talk discusses some activities on terahertz microstructure research at the University of Adelaide. It covers flexible metamaterials, metamaterials in sensing, reflectarrays, plasmonic metamaterials, and coupling effects. The talk also briefly discusses the capability and activities of the Australian National

Title:	Electronic Reconstructions and Correlated Phase Emergence at the LaAlO₃ /SrTiO₃ Interface
Speaker:	Dr A.P. Petrović
Date:	20 February 2014
Time:	4pm - 5pm
Venue:	Hilbert Space
Host:
Abstract:	Electrons are more interesting when they are spatially confined. Upon reducing the dimensionality of a material below 3D, fluctuations, correlations and collective dynamics assume increasing importance, leading to the emergence of a wide variety of magnetic and electronic phases. If a breakage of spatial inversion symmetry is added to this mix, we obtain an enticing recipe for exotic condensed-matter physics with enormous potential for practical applications. With this in mind, few artificial materials present such attractive low-dimensional reduced-symmetry environments as the interfaces between complex oxides such as LaAlO₃ and SrTiO₃ . At the heterojunction between these two band insulators, a variety of carrier injection mechanisms combine to create a nanoscale 2D conducting channel at the top of the SrTiO₃ . The combination of high electron mobilities with easily-modulated carrier densities conjures up appealing visions of fieldeffect devices, but there is so much more to LaAlO₃ /SrTiO₃ than mere conductance switching. Ferromagnetism and superconductivity – two usually antagonistic phenomena – both develop at low temperature; their apparent coexistence and location remain mysterious. Questions also persist over the predominant source of carriers and the “depth” of the interface, i.e. the total distance over which its electronic properties deviate from those of bulk SrTiO₃ . I will give an overview of the current state of research in LaAlO₃ /SrTiO₃ before discussing our recent series of magnetotransport measurements, which reveal the nature of the relationship between ferromagnetism and superconductivity. An inhomogeneous distribution of magnetic dipoles at the interface is shown to create vortices in the superconducting channel below, which are depinned and moved upon reversing the ferromagnetic polarisation. Furthermore, the evolution of the quantum oscillations in the electrical resistance of LaAlO₃ /SrTiO₃ heterostructures with increasing carrier density indicates that the interface induces electronic reconstruction in the SrTiO₃ over a distance of at least 100nm: one order of magnitude further than previously believed. These advances are important steps along the path to hybrid vortex/ferromagnet devices and three-dimensional integration in oxide electronics.

Title:	Probability, physics, and the coin toss
Speaker:	Dr Yong Ee Hou
Date:	19 February 2014
Time:	3pm - 4pm
Venue:	Hilbert Space (PAP-02-02)
Host:	Associate Professor Massimo Pica Ciamarra
Abstract:	Physical problems that involve probabilistic outcomes range from the statistical mechanics of large ensembles of particles to the seemingly simple games of chance such as the toss of a coin and the spin of a roulette wheel. Even in systems with a few degrees of freedom, such as those associated with games of chance governed by deterministic equations of motion, the outcomes can be random due to the amplification of small variations in the initial conditions. We revisited the classic fair 3-sided coin, first solved by John von Neumann, by adding the effects of dynamics to it, and calculate the probability distribution of heads, tails, and sides for a thick coin as a function of its dimensions and the distribution of its initial conditions. Our theory yields a simple expression for the aspect ratio of homogeneous coins with a prescribed frequency of heads or tails compared to sides, which we validate using data from the results of tossing coins of different aspect ratios.

Title:	Statistical Mechanics and Shape Transitions in Microscopic Plates
Speaker:	Dr Yong Ee Hou
Date:	13 February 2014
Time:	4pm to 5pm
Venue:	Hilbert Space (PAP-02-02)
Host:	Associate Professor Massimo Pica Ciamarra
Abstract:	Unlike macroscopic multistable mechanical systems such as snap bracelets or elastic shells that must be physically manipulated into various conformations, microscopic systems can undergo spontaneous conformation switching between multistable states due to thermal fluctuations, Here we investigate the statistical mechanics of shape transitions in small elastic elliptical plates and shells driven by noise. By assuming that the effects of edges are small, which we justify exactly for plates and shells with a lenticular section, we decompose the shapes into a few geometric modes whose dynamics are easy to follow. We use Monte Carlo simulations to characterize the shape transitions between conformation minima as a function of noise strength, and corroborate our results using a Fokker-Planck formalism to study the stationary distribution and the mean first passage time problem. Our results are applicable to objects such as such as graphene flakes or protein β-sheets, where fluctuations, geometry and finite size effects are important.

Title:	Correlation potential of an ion near a strongly charged plate
Speaker:	Dr Lu Bing-Sui
Date:	6 February 2014
Time:	4pm - 5pm
Venue:	Hilbert Space (PAP-02-02)
Host:	Associate Professor Massimo Pica Ciamarra
Abstract:	We analytically calculate the correlation potential and associated correlation energy of a test ion q near a strongly charged plate with dielectric constant e1 , inside an m : - n electrolyte with dielectric constant e. We obtain the following general results: (1) For an infinitely charged plate, the correlation potential (more generally the Green's function) is independent of e1 . (2) For a strongly (but finitely) charged plate, the correlation potential depends on e1 , but this dependence becomes negligible when the distance Dz between the test ion and the plate is much larger than the Gouy-Chapman length m. (3) If the distance to the plate is much smaller than m, the correlation potential is dominated by the the image charge effect arising from the discontinuity of permittivity across the interface. (4) In the regime m « Dz « l, where l is the Debye length, the correlation potential can be interpreted as the energy of interaction between the test ion and an image charge of strength - 3q, and is independent of the valences of ions. (5) The far field asymptotics of the correlation potential explicitly depends on the valences of ions, but is independent of the permittivity of the plate. Analogous to the mean field potential, the correlation potential also exhibits charge renormalization, i.e., at far field the potential appears to emanate from a plate with an amount of charge that tends towards a finite limiting value even though the actual charge density on the plate may be much larger. (6) More importantly, for any asymmetric electrolyte in the far field regime, the correlation potential decays with the same characteristic Debye scale as the mean field potential. This implies the breakdown of the linearized PoissonBoltzmann theory inside bulk asymmetric electrolytes.

Title:	Unraveling the molecular structure of chromatin, one at a time.
Speaker:	Professor John van Noort
Date:	21 January 2014
Time:	2:30 pm - 4pm
Venue:	MAS executive classroom 2
Host:	Associate Professor Phan Anh Tuan
Abstract:	The compaction of eukaryotic DNA into chromatin has been implicated in the regulation of all processes involving DNA. However, the structure of chromatin remains poorly understood. This lack of structural information impedes a functional understanding of chromatin at the molecular level. Here I will discuss recent developments in single molecule force and torque spectroscopy techniques to study this higher order structure. Using magnetic tweezers and reconstituted designer chromatin fibers, we show that such fibers stretch elastically up to three times their rest length. The stiffness is independent of the presence or absence of linker histones. At 3 pN an overstretching transition occurs that can be attributed to simultaneous rupture of nucleosome-nucleosome interactions and DNA unwrapping. For quantitative analysis of the compliance of the fibers we use a two-state model in which nucleosomes are stacked, as found in a folded fiber, or unfolded in a beads-on-a-string fiber. All force induced transitions up to 10 pN can be captured in this simple two-state model. Kinetic analysis of the rupture events suggests that stretching of the histone tails precedes the rupture of nucleosome-nucleosome interactions. Changes in extension upon exertion of torsional stress clearly show that the chromatin fibers fold into a left-handed super-helix. Overall, by new single-molecule force spectroscopy techniques and quantitative analysis of the force-extension behavior of single chromatin fibers we resolved a structural and dynamic picture of chromatin folding.

Title:	Graphene: A Platform for Surface Enhanced Raman Spectroscopy
Speaker:	Dr Jin Zhang
Date:	17 January 2014
Time:	10.30am - 11.30am
Venue:	Hilbert Space (PAP-02-02)
Host:	Assistant Professor Xiong Qihua
Abstract:	Surface enhanced Raman scattering (SERS) imparts Raman spectroscopy the capability of detecting analytes at the single molecule level, but the cost is also manifold, such as loss on signal reproducibility. Despite remarkable steps have been taken forward, presently SERS still seems too young to shoulder the analytical missions in various practical situations. By the virtue of its unique molecular structure and physical/chemical properties, the rise of graphene opens up a unique platform for SERS study. In this talk, the multi-role of graphene played in SERS is overviewed in turn, including a Raman probe, a substrate, an additive and a building block of a flat surface for SERS. Apart from versatile improvements on the SERS performance towards applications, graphene-involved SERS studies are also expected to shed light on the fundamental mechanism of SERS effect.

Title:	Interview with Professor A J Leggett on Physics, Physics Research and the future of Quantum Physics
Speaker:	Professor Leggett
Date:	16 January 2014
Time:	3:30 pm - 4:30 pm
Venue:	SPMS LT2
Host:	Dr Ho Shen Yong
Abstract:	In this informal interview, we will find out more about Professor Leggett’s early days as a Physics student up to the circumstances under which his Nobel prize winning work was conceived. We will also hear from Professor Leggett on unresolved issues in Quantum Mechanics and his views on the future of Quantum Mechanics and Physics research.

Title:	NPL scientists have created the "physics package" of Rubidium atomic clock
Speaker:	Dr G. M. Saxena
Date:	9 January 2014
Time:	4pm - 5pm
Venue:	Hilbert Space (PAP-02-02)
Host:	Associate Professor Rainer Dumke
Abstract:	Their interest was purely academic. After that Saxena worked on other things - theoretical physics and the Cesium Fountain Clock which loses one second in 3,000 years. In 1991, when foreign exchange for this sort of project was in short supply, he "optimized" - repaired and reconditioned - a defective Rubidium Standard Oscillator for the department of Lighthouses and Lightships, saving it money to the tune of 30,000 USD. In 2008, India, unable to procure the clocks from the US, entered into a MOU with NPL to develop the clock. Saxena started work on it again and delivered the first model in 2010 and a second one in February 2011 before retiring in March. "The physics package comes under critical and monopoly technologies," says Saxena. No company in India manufactures this. But the US agreed to sell and India, decided to buy. The Rb atomic clock is also very stable - loses a second in 300 years - and very accurate. And bought from other countries, it's also expensive. Despite having developed the expertise indigenously, India has bought it from the US for about Rs. 1 crore a piece for the Indian Regional Navigation Satellite System. "The Indian one can come for Rs. 20 lakh. The cost of the thing is not much, it's knowledge-based," says Saxena who was hoping that the Space Application Centre (SAC) of ISRO would choose the indigenous product over the imports and develop the space quality model. Apart from in GPS satellites - about three-four clocks go into each - Rb atomic clocks can be used in the telecommunications industry, submarines, Electronics Regional Test Laboratories, test and calibration labs and in the defence.