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Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
Lior M. Burko
- Monday, February 9, 2004
ABSTRACT: The two great mysteries of gravitational physics are the fate of the Universe, and the fate of an astronaut who falls into a black hole. Whereas significant progress has been made recently towards resolving the former mystery (the runaway Universe), the latter suffers from an inherent difficulty: by definition, no observations of the interior of a black hole can be made! I will use Einstein's general relativity to argue that the two seemingly unrelated mysteries are intimately linked. In particular, the question of whether black holes can be used as portals for hyperspace travel (allowing particles - and astronauts - to reemerge from a black hole into a remote part of the Universe, or even another Universe) depends on the cosmological parameters, and in particular on the nature of dark energy. I will also argue that the quantum gravity description of the singularity inside the black hole is perhaps not as crucial for this question, and that emergent classical phenomena might be sufficient to determine the fate of an astronaut embarking on this singular odyssey.
- Wednesday, February 11, 2004
ABSTRACT: Interest in wave propagation in random medium has been constantly growing due to the increasing number of wave objects that can be propagated and studied in random environments. This includes acoustic waves in the Earth's mantle, electromagnetic waves in disordered dielectrics, electrons in quantum dots, and Bose-Einstein condensates in optical potentials. In this talk, two apparent extremes of wave propagation in random media will be discussed and related on the basis of the overarching physical principle governing their behavior - Anderson localization. First, I will present the latest developments in the field of random lasing, in which the localization of photons in random and quasi-periodic structures results in lasing action, which ordinarily is suppressed by disorder. Then, the great potential of using photons as the building blocks of random and periodic media, rather than being exclusively the propagating entities, will be discussed. I will consider the example of the localization of cold atoms in random photonic structures created by light. The advantages and future directions of research along these complementary approaches to the photonics of random and periodic media will be outlined.
Dr. Igor L Kuskovsky
- Wednesday, February 18, 2004
ABSTRACT: Nanophotonics, dealing with optical science and technology at nanoscale, is an exciting new frontier, which provides numerous opportunities both for fundamental research and new applications. Quantum dots (nanocrystals) and nanowires are among the most important building blocks of nanophotnic devices. Therefore, the understanding of underlying fundamental physical phenomena in such structures is very important for future progress in the field.
Mainly two approaches are used to fabricate nanostructures: colloidal chemistry and self-assembly during epitaxial growth. Self-assembled nanostructures are generally divided into two categories, depending on their band alignment: type-I and type-II. We thus present our recent results on both types of quantum dots (QD) and discuss the differences in their optical properties. Moreover, using unique properties of type-II QDs we shall show that there is a smooth transition from isoelectronic centers (few-atom systems) to quantum dots, shedding light on the validity of scaling laws in the "small" size range.
Next, we consider colloidal ZnO nanowires that attracted much interest recently for near-UV lasing applications. It is interesting that there are few reports, if any, on excitonic quantum confinement in such nanowires. We shall present here very recent results on quantum size ZnO nanowires and discuss the difficulties with observing quantum size effects in this material.
- Monday, February 23, 2004
ABSTRACT: Optical phenomena below the diffraction limit of light have been challenging scientist with increasing importance since 1930. Photonic band-gap (PBG) structures found a strong applied research interest for telecommunication applications in the last years. PBG's could be used as potential switching and connecting units. Alternatively, PBG structures could be the access to future in-vivo Fluorescence Correlation Spectroscopy (FCS) for biomedical diagnosis, increasing the speed of several orders of magnitude. Pharmaceutical screening could also strongly be improved. The centre of the hardware of such systems is the nano-structured device embedded in connecting functional Microsystems. In this talk we focus on the comparison of flexible nano-structure fabrication methods for research and development and rapid prototyping with parallel processing methods for high throughput nano-optical device fabrication.
Focused Electron Beam (FEB) induced deposition of materials allows the extremely flexible brick by brick growth of a huge variety of structures in a serial process. The minimum "brick" size is of the order of 20 nm, and the surface roughness below 1 nm. The index of refraction of the deposit is predominantly determined by the choice of the chemical precursor and to a much less extend by the physical deposition parameters. Modified Scanning Near Field Optical Microscopy (SNOM) tips of non-spherical FEB deposits of gold nano-composite material allowed measuring frequency shifts in the transmission spectra, consistent with surface plasmon excitation calculations. Realization of photonic band-gap structures will be presented.
Parallel processing by electron beam lithography and deep reactive ion etching (DRIE) or lift-off processes that are well known from microelectronics industry have to be adapted to nano-optics, as the materials and the aspect ratio's differ strongly between the applications. 150 nm thick gold lift-off structures resulted in subwavelength confined enhanced light emission.
- Wednesday, February 25, 2004
ABSTRACT: Random Telegraph Signals (RTS) in transport current through a conduction channel of a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) are known to be related to charging and discharging of a single impurity due to electron tunneling between the impurity and the channel. The phenomenon provides a unique example where a single electron tunneling can be explicitly monitored. Recent experiments have shown that the RTS in MOSFETs turns out to be strongly dependent on applied magnetic fields, which offers a possibility to manipulate by a spin of a single electron. The latter possibility is of a primary importance for newly developing areas of research such as spintronics and quantum information processing (AKA quantum computing).
In my presentation I will outline our proposal to detect single spin resonance in the system and will present recent experimental results of our colleagues (at UCLA) based on the proposed scheme. I will also discuss certain theoretical results of our research in the field, which include the explanation of unexpectedly large RTS timescales and anomalous magnetic behavior of RTS systems at low temperatures.
Vinod. M. Menon
- Monday, March 1, 2004
ABSTRACT: In this talk, we will describe a photonic integration platform known as asymmetric twin guide (ATG), whereby any combination of waveguides, modulators, couplers, lasers, optical amplifiers, detectors, etc. can be "laid out" on a chip using CAD-based design to meet the requirements of a particular application. The designs are then realized on standard, non-regrown, epitaxial wafers followed by standard semiconductor fabrication processes. The integrated photonic devices have performance equal to discrete components. In this context, we will present our recent results on various monolithically integrated photonic circuits that have been developed in our group like all-optical wavelength converter based on Sagnac interferometer geometry, waveguide photodiode with integrated semiconductor optical amplifier, chip-scale demultiplexer using arrayed waveguide grating with integrated photodiodes, and microring resonators with integrated gain elements. Some novel physical phenomena observed in these integrated devices like non-reciprocity of counterpropagating signals in the Sagnac interferometer and control of quality factor and critical coupling in microring resonators will also be addressed. Finally, we will briefly discuss nano/micron-scale photonic circuits that will have possible applications in quantum information processing.
- Wednesday, March 3, 2004
ABSTRACT: The complex interplay between magnetism and superconductivity is a central topic in condensed matter physics due to increasing evidence indicating that unconventional superconductivity (SC) occurs in the vicinity of magnetically ordered states. The experimental observations inspired models proposing "magnetically mediated" SC pairing in the proximity of magnetic quantum-criticality in a variety of systems, ranging from heavy Fermion-intermetallics to high- TC superconductors . In this context, the report of magnetic field-induced superconductivity (FISC) [2,3] in the magnetic layered organic conductor l-(BETS)2FeCl4 constitutes, perhaps, an unique example of a cooperative interaction between both types of orderings, where field-induced ferromagnetism becomes the essential ingredient for stabilizing SC at low temperatures and at very high magnetic fields in an otherwise antiferromagnetic insulator. Here we will briefly revise the current status of organic superconductivity as well as the discovery and the properties of the FISC state. We will show that its phase-diagram can be well described in terms of the so-called Jaccarino-Peter effect  if the quasiparticle nature of the charge carriers is also taken into account. The resulting phase diagram suggests the existence a 2-D Larkin-Ovchnikov-Farrel-Fulde "textured" superconducting sub-phase which only recently has been claimed to exist in the CeCoIn5 compound . The discovery of FISC in an organic compound has lead to interesting developments in the area of nanotechnology  and we suggest that it may lead to technological applications.
 See for example, A.V. Chubukov, D. Pines, and J. Schmalian, cond-matt/ 0201140 and references therein.
 S. Uji et al., Nature (London) 410 , 908 (2001).
 L. Balicas et al. , Phys. Rev. Lett. 87 , 67002 (2001).
V. Jaccarino and M. Peter, Phys. Rev. Lett. 9 , 290 (1962).
 H. A. Radovan et al. , Nature, 425 (6953), 51 (2003): A. Bianchi et al. ,Phys. Rev. Lett. 91 , 187004 (2003).
 M. Lange et al. , Phys. Rev. Lett. 90 , 197006 (2003).
- Monday, March 8, 2004
ABSTRACT: One of the most exciting recent experimental discoveries in condensed matter physics has been the observation of the oscillatory magnetoresistance and the zero resistance of a 2D electron gas subject to microwave radiation. For microscopic understanding of this phenomenon we derive the quantum Boltzmann equation for the two-dimensional electron gas at large values of the filling factor. This equation describes all of the effects of the electric fields on the impurity collision integral, including Shubnikov-de Haas oscillations, smooth part of the magnetoresistance, and non-linear transport. We use this equation to analytically analyze the effect of the external microwave radiation on the electron transport. Particularly, we show that the dominant contribution to the observed oscillatory magnetoresistance originates from the non-equilibrium component of the electron distribution function rather than from the corrections to the matrix elements of electron scattering off disorder due to the microwave field.
Suryanarayan G. Hegde
- Wednesday, March 10, 2004
ABSTRACT: The non-contact, quasi-static technique presented involves biasing the silicon wafer with the gate dielectric by depositing charge (from a corona source) and measuring the surface voltage and surface photovoltage (via illumination) using a Kelvin Probe.
The main parameters of measurement presented are: Equivalent Oxide Thickness (EOT), Leakage Current, Flatband Voltage, Density of Interface Traps (Dit) and Soft Breakdown Field. EOT and Dit measurements were chosen for the metrology of gate dielectrics for manufacturing application. Density of Interface Traps, in particular, is an important parameter for qualification of the interface between the dielectric and the semiconductor.
Dit is very sensitive to interface roughness, presence of intrinsic defects or extrinsic impurities all of which can be attributed to particular technique of the growth of the dielectric, silicon implantation specifics, annealing details etc. Examples of gate dielectrics from recent IBM/Infineon Logic and DRAM technologies will be presented.
Note: This talk is based on the work by the author while at IBM Research Division.
- Monday, March 15, 2004
ABSTRACT: As the dimension shrinks to nanometer scale, contacts between metal electrodes and molecules play a much more important role than those in bulk. Effects of "surface states" could spread through the whole nano-electronics system. Here we discuss (i) How to form electric contacts to single molecules, and (ii) How contacts between single-walled carbon nanotubes (SWNTs) and metal electrodes control the properties of carbon nanotube field effect transistors (NT-FETs).
- Wednesday, March 17, 2004
ABSTRACT: A description of the properties of low dimensional electron gases remains one of the most important and challenging problems in condensed matter physics. I will present electron transport and tunneling measurements on ultrathin, metal films. I will show that in the strong disorder limit a gap emerges in the density of states that is solely attributable to fundamental many body electron-electron interaction effects, i.e. the Coulomb gap.
Interestingly, a quantum metal state can be realized, in otherwise highly insulating films, by suppressing the Coulomb gap via a magnetic field. In the second part of my talk I will describe ongoing research into the properties of the two dimensional electron gas of Field Effect Transistors (FETs) fabricated on high quality organic molecular single crystals.
Practical optoelectronic applications of the molecular organic materials, such as flexible, large-area electronic devices will also be discussed.
- Wednesday, May 12, 2004
ABSTRACT: Physics of nanosized structures has grown extensively in a recent past. Nanosized structures are developing very quickly, because many applications in nano-optics, nano-electronics etc. become more realistic in view of possible applications. In this talk will be presented some studies of the optical properties of nanosized metallic particles, organized arrays of empty or metal filled nanopores, ordered mesoporous silica films and colloidal suspensions. These objects were studied by scattering, reflection, and transmission of volume and surface electromagnetic waves.
Tom C. Weinacht
- Friday, September 17, 2004
ABSTRACT: Learning to control molecular fragmentation using tailored laser pulses" Ultrafast laser pulses allow us to view atomic and molecular dynamics with time resolution on the order of 10-14 s. Recent advances in laser technology allow us to tailor the electric field of an ultrafast laser pulse and to amplify the pulse to intensities above the atomic unit of intensity. Intense shaped pulses allow us to move from observing to controlling atomic and molecular dynamics.
I will discuss experiments which use shaped ultrafast laser pulses to control molecular fragmentation. The experiments make use of a Genetic Algortihm to discover optimal pulses for control. Our efforts are focused on trying to understand the physical control mechanisms underlying solutions uncovered by the algorithm. Experiments in progress and future experiments will be discussed.
- Monday, October 4, 2004
- Monday, October 18, 2004
- Tuesday, October 19, 2004
- Monday, October 25, 2004
ABSTRACT: Decreasing feature sizes due to advances in nanotechnology place a premium on careful treatment of phase, length, and time in optics. All three quantities are intermeshed due to morphology at the nanometer length-scale. After examining the characteristics of the responses of columnar thin films and chiral sculptured thin films to optical pulses and beams, the thesis that nanotechnology for optics is a phase-length-time sandwich is put forward.
- Monday, November 1, 2004
- Monday, November 15, 2004
- Monday, November 22, 2004
- Monday, November 29, 2004
- Monday, December 6, 2004
ABSTRACT: An intrinsic feature of Mott insulators is that doping, i.e., changing the particle density, can dramatically affect their properties. I will report on our discovery of charge-doping controlled ferromagnetism at room temperature in self-assembled vanadium oxide nanotubes. By adding either electrons or holes, the initially spin-frustrated nanotubes develop a nearly identical nonlinear ferromagnetic spin response, demonstrating a novel unexpected electron-hole complementarity in the nanotube structures. The underlying picture is that, on doping, the Fermi level is swept through the Mott gap in this multiband strongly correlated system, removing the frustration responsible for the spin-gap. Itinerant carriers under spin control are produced in one vanadium Hubbard band which strongly interacts with other more localized vanadium spins. These findings show a path to new spin-aligned nanoscale building blocks, where the Fermi level sweep can be accomplished by applied voltage.