Session K1: Poster Session II (2:00-5:00PM)

Integrated High Switch Test System to Determine Time-Dependent Dielectric Breakdown

As a 2011 SPS summer intern, I worked for NIST in the Semiconductor Division learning about characterizing defects in MOSFETs. The lifetime and reliability of a MOSFET is directly related to the projected lifetime of an electronic device. By applying an increased stress voltage to the gate oxide, the lifetime of the MOSFET within an electronic device can be simulated. From this simulation, the reliability of the device can be determined from a mathematical extrapolation which is derived from breakdown data. Although time dependent breakdown has been thoroughly studied in the past in silicon dioxides, large statistical studies are still necessary to confirm the already accepted models for extrapolating mean lifetimes as well as increasing the accuracy of the projected lifetime. By creating an integrated high switch test system to determine time dependent dielectric breakdown, we hope to create a more affordable and efficient system to test copious numbers of oxides. This system is composed of set of highly parallel switches which apply a stress voltage to a total of 48 oxides. By implementing LabVIEW, the level of the stress voltage as well as the break down voltage and time can be determined. From this data further statistical analysis can be applied.   

Out of the Box Thinking: Kinematics from a 163 Million-Year-Old Dinosaur Trackway

Dinosaurs always grab the interest of students. Information about dinosaur locomotion is accessible from the trackways they left. In a unique connection to kinematics, evidence of the acceleration of a meat-eating dinosaur (theropod) is evident in Trackway 13 in Ardley Quarry in Oxfordshire, UK. This particular trackway is described by J.J. Day, D.B. Norman, P. Upchuch and H.P. Powell in Vol. 415 of Nature on pages 494 and 495, published in 2002. This particular theropod underwent an acceleration of about g/3. This example provides a fun and engaging exercise for students studying kinematics.   

Polyaniline-Carbon Nanotubes Composite Actuators

The understanding of photoactuation in Carbon Nanotubes (CNT)-polymer composites can contribute to the development of micro- and nano-optical-mechanical systems for applications that include intracellular motors, artificial muscles, and tactile displays for blind people. The integration of CNTs into polymers combines the good processability of polymers with the functional properties of CNTs. CNTs-polymer composite fibers were fabricated using the electrospinning technique. electrospinning process orients the CNTs along the precursor stream and can contribute to enhance photo actuation properties. The addition of polyaniline, an electroactive conductive polymer is expected to enhance the actuation strain of the composite. aim of this research is to study photoactuation in MWCNT-Polyanilile electrospun fibers. fibers were characterized using Scanning Electron Microscopy, Atomic Force Microscopy, and X-Ray Diffraction. Results demonstrate evidence of photo-actuation after irradiating the fibers with visible light. tests are being conducted to understand the mechanisms of the composites response to light stimulation.   

Using the IPAD as a Pedagogical Tool: Focus on Angular Motion Analysis with Real-World Applications

The IPAD is a portable, novel interface that has the potential to create a more interactive learning environment in undergraduate physics education, particularly in the introductory physics laboratory setting. We report our experience in using this pedagogical tool in an algebra-based physics laboratory course, focusing on its application in analysis of angular motion. Taking advantage of its portability, we use it to analyze motion not only using standard physics laboratory equipment but using it for analyzing motion in real-world applications such as with exercise equipment such as an exercise bicycle and an elliptical machine. We report on student response to this learning tool.   

Why Physics Programs are Slimming Down

We study the Physics enrollment in the light of the current financial situation. Role of the Physics program in the growth of several programs in a university and the importance of a successful Physics program to prepare for the future needs of the time are analyzed in detail. The effect of shutting down of Physics programs will also be discussed.   

Student Autonomy and its Effects on Student Enjoyment in a Traditional Mechanics Course for First-Year Engineering Students

In light of recent literature in educational psychology, this study investigates instructional support and students' autonomy at a small technical undergraduate school. Grounded theory is used to analyze twelve semi-structured open-ended interviews about engineering students' experiences in \textit{Introductory Mechanics }that includes\textit{ Lecture}, \textit{Recitation}, and \textit{Laboratory} components. Using data triangulation with each course component as a unit of analysis, this study examines students' course enjoyment as a function of instructional support and autonomy. The\textit{ Lecture} utilizes traditional instructor-centered pedagogy with predominantly passive learning and no student autonomy. The \textit{Recitation} creates an active learning environment through small group work with a moderate degree of autonomy. The \textit{Laboratory} is designed around self-guided project-based activities with significant autonomy. Despite these differences, all three course components provide similar levels of instructional support. The data reveal that students enjoy the low autonomy provided by \textit{Lecture and Recitations }while finding the \textit{Laboratory} frustrating. Analyses indicate that the differences in autonomy contribute to students' misinterpretation of the three course components' value within the context of the entire course.   

Does requiring graded online homework improve physics exam performance?

In a first experiment with using Mastering Physics in a first semester calculus-based course, homework and exam performance was tracked periodically during the semester. As expected, the use of novel technology (and its ability to track which students were persistently working at problem exercises) motivated many students to become more involved with work on assigned physics problems. Although there did appear to be a significant correlation between exam averages and homework scores in the upper half of the exam average distribution, individuals spanning the full range of exam averages (down to 45 percent) earned homework scores as high as those who had performed outstandingly well in exams. In this work, we present results and proposed plausible explanations for the apparent anomaly.   

Preparation and characterization of optically-active metal probes for tip-enhanced Raman spectroscopy

Tip-enhanced Raman spectroscopy (TERS) has enabled spatially correlated topographic and chemical imaging of biomolecules, catalysts, photovoltaics, and materials on the nanoscale. Critical to the TERS experiment is the tip; tip size sets the spatial resolution, whereas tip material and shape determine how well far-field laser light couples to electron oscillations (plasmons) in the tip to create a tightly confined field that enhances Raman scattering of molecules in the tip-surface gap. Tips are typically prepared via electrochemical etching of metal wires in strong acid or base solutions. This etching process is not well understood, and the production of sharp, plasmonically active tips remains a key challenge in the TERS field. To address this issue, we developed an electrochemical etching cell with diagnostic system based on a tuning fork oscillator to evaluate the tip-etching process. We present initial study of oscillation dynamics during electrochemical tip etching under varying conditions.   

Electrical and Magnetic Properties of Nanostructured Mo-Doped Yttrium Iron Garnet

Yttrium Iron Garnet (YIG) is a synthetic garnet and ferromagnetic with the chemical formula Y$_{3}$Fe$_{5}$O$_{12}$. In YIG, five iron (III) ions occupy two octahedral and three tetrahedral sites, with yttrium (III) ions coordinated by eight oxygen ions in an irregular cube. The iron ions in the two coordination sites exhibit different spins, resulting in magnetic behavior. It is also transparent to infrared wavelengths over 600~nm. Nanostructured YIG has been synthesized systematically by solid state reaction method. The formation of pure YIG have been investigated through X-ray diffraction (XRD) beginning from weighing in molar proportions of Y$_{2}$O$_{3}$ and Fe$_{2}$O$_{3}$, mixing and grinding, pre-sintering and final sintering at 1300 $^{\circ}$C. XRD study shows that YIG exhibits cubic structure with lattice constant of about 12 {\AA}. Magnetization with varying field and temperature has been measured using a SQUID magnetometer. Room temperature dielectric measurements indicate that the YIG shows the usual dielectric dispersion. Magnetic studies of Mo YIG has shown that it becomes diluted after doping and dielectric measurement have shown that dielectric constant of that sample has been reduced.   

Water on a Hydrophobic Surface: Contact Angle vs. Depletion Layer

Hydrophobic surfaces repel water. When this occurs, a depletion layer is formed between the water and the hydrophobic surface. We will be studying the effects from the contact angle, the angle at which the water droplet meets the surface, on the depletion layer. Larger contact angles create thicker depletion layers, which has lead us to determine if there is a direct relationship between the contact angle and depletion layer. In order to do this, we will be coating gold slides with a hydrophobic ODT solution, a hydrophilic Mercapto solution, and various mixtures of both of these solutions to create a large range of contact angles. We will be using Surface Plasmon Resonance to study to any depletion layer created by water on these surfaces.   

SPS Fabric of the Cosmos Cafe

Hosted by Brian Greene and based on his best-selling book of the same title, \textit{The Fabric of the Cosmos }is a new four- part NOVA series that explores the deepest mysteries of space and time. The program was kicked-off by 30 ``Cosmic Cafes'' being held around the country funded by an NSF grant which allows SPS-NOVA to fund SPS chapters for these events. During the summer I assisted in planning this kick-off, reviewing and suggesting revisions of resources related to the NOVA series to make them relevant to an SPS audience. I also got to organize and moderate the first ``Cosmic Cafe.'' The Cosmic cafe that I organized was discussion based, with our speaker Dr. James Gates starting with a short talk and then opening the floor up for questions. By organizing a ``Cosmic cafe,'' I got real hand experience about the challenges an SPS chapter would face while organizing a cafe themselves. Based on my experience I shall also discuss the effectiveness of the first ever themed science cafe blitz. A science caf\'{e} is an informal discussion with an expert in a very casual location, usually a restaurant, coffee shop, or a bar. A science cafe is mostly discussion based, but has a lot of freedom for the format. A ``Cosmic'' cafe is a science cafe which is based around the topics discussed in the documentary ``The Fabric of the Cosmos.''   

Water on a Hydrophobic surface

Hydrophobicity, meaning literally fear of water, is exhibited on the surfaces of non-stick cooking pans and water resistant clothing, on the leaves of the lotus plan, or even during the protein folding process in our bodies. Hydrophobicity is directly measured by determining a contact angle between water and an objects surface. Associated with a hydrophobic surface is the depletion layer, a low density region approximately 0.2 nm thick. We study this region by comparing data found in lab using surface plasmon resonance techniques to theoretical calculations. Experiments use gold slides coated in ODT and Mercapto solutions to model both hydrophobic and hydrophilic surfaces respectively.   

Correlation between acoustic emission and mechanoluminescence of rock cores under quasistatic compression

When a rigid solid undergoes mechanical deformation, locally accumulated strain energy can be released through multiple avenues including acoustic emission (AE) and light emission known as mechanoluminescence (ML). In AE, events within a stressed rock such as defect movement, grain boundary shifting, and crack propagation create pressure waves which can be detected at the rock surface. While AE is used extensively for rock evaluation in geophysics, civil engineering, and mining, ML by comparison has received little attention from the geoscience community. ML from stressed and fracturing rock has been observed in mines, earthquakes, and the laboratory, but the underlying mechanism behind ML is poorly understood. Possible candidates include defect movement, creation of charged surfaces during fracture, piezoelectrification, and triboluminescence. Observing whether a correlation exists between ML and AE will help determine the source of ML. We have designed an apparatus for AE and ML detection of rock cores under quasistatic compression. Using photomultiplier tubes and piezoelectric transducers, AE and ML events can be spatially and temporally observed and correlated. We present apparatus design and preliminary results.   

Harpoon-based sample Acquisition System

Acquiring information about the composition of comets, asteroids, and other near Earth objects is very important because they may contain the primordial ooze of the solar system and the origins of life on Earth. Sending a spacecraft is the obvious answer, but once it gets there it needs to collect and analyze samples. Conceptually, a drill or a shovel would work, but both require something extra to anchor it to the comet, adding to the cost and complexity of the spacecraft. Since comets and asteroids are very low gravity objects, drilling becomes a problem. If you do not provide a grappling mechanism, the drill would push the spacecraft off the surface. Harpoons have been proposed as grappling mechanisms in the past and are currently flying on missions such as ROSETTA. We propose to use a hollow, core sampling harpoon, to act as the anchoring mechanism as well as the sample collecting device. By combining these two functions, mass is reduced, more samples can be collected and the spacecraft can carry more propellant. Although challenging, returning the collected samples to Earth allows them to be analyzed in laboratories with much greater detail than possible on a spacecraft. Also, bringing the samples back to Earth allows future generations to study them.   

AIP Career Pathways

American Institute of Physics (AIP) Career Pathways is a new project funded by the National Science Foundation. One of the goals of AIP Career Pathways is to prepare students to compete for Science, Technology, Engineering, and Mathematics (STEM) careers with a bachelor's degree in physics. In order to do so, I reviewed and compiled useful resources on finding a STEM career with a bachelor's degree in physics. These resources not only supply the job seeker with job postings in STEM careers but also provide them with information on resumes, interviewing skills, and networking. Recently at the 2011 Industrial Physics Forum, I interviewed companies in the private sector to obtain a unique perspective on what types of skills potential employers expect an applicant to posses with a bachelor's degree in physics. Ultimately, these components will be used as supplements at student career workshops held at annual Society of Physics Students Zone Meetings.   

Simulation of a Tunable, Three-dimensional Resonant Cavity for Quantum Control and Measurement

We present the design and simulation of a tunable, superconducting, three-dimensional resonant cavity for control and measurement of quantum systems. By adjusting the dimensions of the cavity appropriately, we create a photon resonant mode in the 4-8 GHz frequency band, typical of many current superconducting qubits. We simulate the resonance behavior of the cavity using a commercial three-dimensional finite-element solver to explore the effects of various modifications of the cavity boundaries and coaxial signal ports, as well as the insertion of dielectric materials and metallic control lines within the cavity. In particular, we find that the quality factor of the cavity resonance is exponentially dependent on the insertion depth of the port pins from the surface of the cavity. A weak dependence is observed for other modifications. By adjusting the pin depth, we can achieve a range of quality factors from a few hundred to a few million, as verified by experiment.   

Suspended Particle Mass Determination from Transport Coefficients

It has long been known that a suitable combination of transport coefficients can be used to determine particulate mass in suspensions. Advances in particle tracking make this straightforward and easier to apply to large numbers of particles. This poster will concern recent experiments along these lines, which are devoted to improved understanding of composite, hybrid, core-shell colloidal particles, without regard to shape.   

Electromagnetically Induced Transparency in a Four-Level W Scheme: Effect of Beam Intensity and Phase on Propagation

Co-propagation of two circularly polarized lasers in an electromagnetically induced transparency four-level W scheme is investigated. Our four level system is produced using the ground state and three Zeeman levels of ultracold magnesium atoms. Parameters are determined such that co-propagation of the two incident optical fields will occur. Group velocities obtained by solving the density matrix master equation for the appropriate coherences are found to be periodic with respect to the phase angle of the Rabi frequency.   

Fluorescent security markers on ZnO nanowires

Zink oxide is an efficient emitter of light thanks to the large exciton binding energy of 60 meV. The narrow emission lines from ZnO nanowires can be used as an enhanced security feature in documents and can be easily recognized from the background originating from the paper itself. We have studied the emission properties of ZnO nanowires in the UV range and how they can be implemented into paper products for document security. The zinc oxide nanowires were synthesized by chemical vapor transport and postprocessed in solution. The nanowires were dispersed using a sonicator into nitric acid water solutions with a pH of 2 and 4, and ammonium hydroxide water solution with a pH of 5 and 7. The morphology of the dispersed ZnO nanowires was imaged under a scanning electron microscope. Fluorescence measurements have shown better light emission from the nanoparticles dispersed in the basic pH solution. This material was then implemented into crafted paper and viewed under UV lamps and with a spectrometer. We have studied the loading of the paper with ZnO nanoparticles. A comparison was done with equivalently processed material of ZnO in powder form. The implementation of zinc oxide nanowires into paper products can advance document security at a relatively low cost.   

Noise correlations in quasi-1D conductors with different contact geometries

We nanofabricated end contacts to mesowires of NbSe$_{3}$ and tested for the presence of correlations in noise spectroscopy at various temperatures below Peierls transition temperature. We find that for 1/$f$-like, broadband noise (BBN), the degree of correlations in transport in two segments along a NbSe$_{3}$ mesowire can be tuned with electric field and temperature. For standard, bottom/top contacts geometries, we see a limited degree of correlations for narrow band noise (NBN) (typically 20-30{\%}, except for a limited range of temperatures), but we also see that end contact geometry enhances the degree of correlations for NBN signal (closer to 50{\%}). We believe this phenomenon is related to a better control of the CDW transport, such as weaker temperature dependence of condensate current. We also explore the issues of the overall energy transfer through such contacts.   

Intensity dependent photoluminescence studies on zinc oxide nanowires

The ZnO nanowires were grown by the chemical vapor transport method using a thin gold film as a catalyst. Their light emission in the visible and near UV spectral range was studied using excitation sources with large variation of the pump intensity, e.g. Xenon lamp, UV LEDs, nitrogen laser. The photoluminescence spectrum consists typically of the exciton emission band and a defect related band in the green spectral range. We have observed drastic change in the photoluminescence spectrum at high pump intensities with drastically decreased intensity of the defect related band. The results have been interpreted within a model accounting for the surface effects and associated band banding at the surface. Cathodoluminescence measurements of ZnO nanowires and bulk films were performed, which support the proposed model.   

Specific Heat of Two-Gap Extreme Type-II Superconductors in High Magnetic Fields

We present a numerical study of the quasiparticle contribution to the low-temperature specific heat of an extreme two-gap type-II superconductor at high magnetic fields. Within a T-matrix approximation for the self-energies in the mixed state of a homogeneous superconductor, the electronic specific heat is a linear function of temperature with a linear-$T$ coefficient $\gamma (H)$ being a nonlinear function of magnetic field $H$. We compare our theoretical curve with available experimental data for the two-gap superconductors NbSe$_2$ and LuNi$_2$B$_2$C.   

Changes in Ocean Color at Puerto Rico due to Tropical Storms

In this research we analyze the impact of tropical storms in the ocean color of the Puerto Rico coast. The changes in ocean color are due to the absorption and scattering of light. It has been shown that remote sensing techniques are used as a fast and economical way to study the concentrations of phytoplankton and other water constituents at the ocean. Data from MODIS (Moderate Resolution Imaging Spectroradiometer) were used to generate images of ocean color. The images were downloaded from internet and processed using the program developed by NASA called SeaDAS. The processing involved the standard atmospheric correction and algorithm application. Dramatic changes in ocean color were detected due to tropical storms Earl and Jeanne. The results support the use of remote sensing in this type of assessments.   

High aspect ratio cell probes based on ZnO nanowires

ZnO is a useful and versatile material being used in nanotechnology and has many potential applications as a material in nanoscale biotechnological devices. The growth of ZnO nanowires using a gold catalyst has been extensively researched. In this project we propose an alternative growth method using electrophoretically deposited gold nanoparticles as a catalyst, rather than use of the more common gold thin film catalyst, in order to grow ZnO nanowires. Colloidal Au nanoparticles approximately 25 nm in diameter are used as the catalyst source and 0.003" diameter tungsten wire as the substrate. The gold nanoparticles were deposited on the tip of the tungsten wire by electrophoresis. The ZnO nanowires were deposited by chemical vapor transport process in a three zone tube furnace. Scanning electron mi croscopy was used to image the nanowires and energy dispersive X-ray spectroscopy to analyze the composition of the probes. We will illustrate our approach on electrically insulating the probe so that only the very tip can probe electrically the interior of biological cells.   

Laser Induced Fluorescence Studies of New Liquid Crystal C16-Fluorescent Dipyrrinone

A new liquid crystal, C-16 Fluorescent Dipyrrinone, was synthesized and its absorption and fluorescence properties investigated near the phase transitions. A sample of the liquid crystal was dissolved in chloroform and deposited on a glass slide and housed in a temperature controlled environment. Fluorescence was induced by pumping the sample at 355nm from a frequency-tripled, pulsed ND:YAG laser and was analyzed using a monochromator and a 1GHz oscilloscope. The sample was held at each temperature, from 30\r{ }C to 80\r{ }C, with 1 mK precision before taking the spectra. The results show significant changes in the peak in the spectra near the phase transitions, allowing for precise measurement of the phase transitions. The samples were further characterized by measuring their absorption spectrum at different temperatures in the range of 30-60\r{ }C was recorded over the spectral region 300-800 nm.   

Absorption and Fluorescence Study of New Liquid Crystal C14-Fluorescent Dipyrrinone

A new liquid crystal, C14-Fluorescent Dipyrrinone, was synthesized and its fluorescence and absorption properties were studied near the phase transitions. A frequency-tripled, pulsed ND: YAG laser was used to induce fluorescence in the liquid crystal sample. The fluorescence spectra and decay times were studied as functions of temperature using a 1GHz oscilloscope, monochromator, and photomultiplier tube. This sample was tested over a temperature range of 30-60\r{ }C with 1~mK resolution to allow precise determination of the phase transitions of the sample. The absorption spectra were recorded over the temperature range of 30 -- 50$^{0}$C using a HP 8453 UV-VIS spectrometer, on a sample of the liquid crystal dissolved in chloroform and dried on a quartz insert.   

Resonance Circuit with a Nonlinear Liquid Crystal Capacitor

The liquid crystal 4'octyl-4-cyanobiphenyl (8CB) was injected into a commercially available liquid crystal capacitor cell (INSTEC, Inc). The cell was housed in a temperature-controlled environment constructed in the lab and a resonant circuit was assembled using the 8CB capacitor. The temperature of the capacitor was varied over the range 25\r{ }C to 45\r{ }C, covering the smectic, nematic, and isotropic phases. The sample was held at each temperature with a precision of 1mK before measuring the resonance curve with a network analyzer. The results showed a non-linearity in the resonance curve in the nematic phase, distorting the shape of the resonance curve. The corresponding curves for the smectic and isotropic phases were linear.   

Optical Absorption and Laser Induced Fluorescence Studies of Liquid Crystal C-10 Fluorescent Dipyrrinone

A newly synthesized liquid crystal C-10 Fluorescent Dipyrrinone was dissolved in chloroform and allowed to dry on a glass slide. The slide was housed in a temperature controlled environment constructed in the lab\textbf{. }A frequency-tripled pulse ND: YAG laser (355 nm) was used to induce fluorescence in the liquid crystal sample, which was analyzed using a monochromator, photomultiplier tube, and a 1GHz oscilloscope. The sample was tested over a temperature range of 30-70$^{0}$C. The temperature control was precise to within 1 mK, allowing precise determination of the phase transition temperatures. The area, fall time, and peak values of the fluorescence signal were studied as functions of wavelength and temperature. Absorption spectra in the spectral range 300 -- 800 nm were also recorded using a commercial (HP8453) UV-VIS spectrometer.   

Analysis, Reconstruction, and Modeling of the Electrical Signal of the Weakly Electric Fish \textit{Apteronotus Leptorhynchus}

The weakly electric fish \textit{Apternotus leptorhynchus} uses approximately sinusoidal electrical signals to electrolocate and electrocommunicate. In particular, the complex electrical signals which are generated during dynamic interactions have been shown to impact the behavior and physiology of interacting fish. In order to study the specific features of these electrical signals that are biologically relevant, signals collected from fish under diverse conditions are analyzed using temporal and spectral techniques, specifically amplitude variation and frequency variation. Having characterized specific features of the signals, computational methods are then used to construct signals to mimic real electric fish signals. Constructed signals show close matching in relevant features when analyzed in the same manner as the original signals. From a different perspective, a two-dimensional dynamic model is formulated to simulate the generation of amplitude modulation in these signals based on the motion of a particle sampling a generalized field of time-varying points and found to generate some features of experimental electric fish signals. Work continues on both analysis, reconstruction, and modeling as well as actual playback experiments to determine the impact of these signals to influence fish neuroethology.   

The WASTED Resolutions: exploration of the spatial and energy limits of the Webcam Alpha Spectrometer TEchnology Demonstrator

Scientists and engineers build simple, low-cost, webcam-based instruments for use in many disciplines. Analysis of the optical signal received through the three broadband color filters -- red, green and blue -- form the basis of many of those instruments. The CMOS sensors in webcam pixels also produce signals in response to ionizing radiations -- such as alpha particles from a radioactive source. Simple alpha radiography has been demonstrated with an alpha source and a webcam modified to expose the sensors. The performance of the Webcam Alpha Spectrometer TEchnology Demonstrator (WASTED) built from such a modified webcam and a commercially available alpha source mounted to an optics rail is analyzed in terms of the energy upper-half-width-half-maximum and of the spatial modulation transfer function.   

Temperature and polarization dependent photoluminescence studies of WO$_{3}$ and WO$_{3}$-x single crystals

WO$_{3}$ is an important material not only due to its interesting electronic properties but also due to applications in electrochromic devices and energy storage. The mechanism behind the electrochromic effect has been debated for several decades [1]. We have studied two WO$_{3}$ single crystals, a transparent and doped WO$_{3}$-x. A photoluminescence center around 865 nm is observed after sub-band gap excitation at 405 nm with relatively higher intensity in the crystal containing oxygen vacancies. The center appears as a broad transition of 35 nm FWHM and does not follow the band gap energy with temperature. However polarization dependent studies reveal at least two polarization dependent components of the center. To further investigate the polarization dependence for the two WO$_{3}$ crystals, we will use samples for which the orientation of the high axis of symmetry is known.   

Raman spectroscopy investigation in the NWA 3118 meteorite: Implications for planet formation

Planet formation involves the coagulation of micron-scale dust into centimeter-meter scale objects. Explanation is sought of the adhesion property of the dust aggregates ultimately leading to the formation of structures like planetesimals. Confocal raman microscopy has been used to investigate carbon structures on the NWA 3118 meteorite. It is a carbonaceous type CV3 meteorite composed of micrometer scaled structures like chondrules and inclusions embedded in the matrix material. Raman mapping of meteorite samples with a laser of excitation wavelength 488nm was pursued, with a focus on the interfaces between chondrules and the matrix. Raman spectra of olivines and graphitic structures with corresponding optical and raman images of the spotted structures in the NWA 3118 are reviewed.   

Formation of wave packets in electron diffraction on crystals

Measurements of electron diffraction typically reveal the atomic structure of crystals and allow finding the length of chemical bonds. The effective electronic charge of each atom in the crystal acts upon the incident electron beam as a netting of narrow pinholes, and Fourier transforms the unique deBroglie wavelength of the projectile electron accelerated at fixed voltage into a wave packet. Using the uncertainty principle one can understand the mechanism that makes an incident electron to become a wave packet travelling inside the crystal at a group velocity identical with the initial speed of the projectile electron. Furthermore, the Pauli Exclusion Principle allows us to understand the fast passage of the projectile electron through the crystal and also, it allows the evaluation of the characteristic time for electron transmission. The project was sponsored by the STAIRSTEP program under the NSF-DUE grant{\#} 0757057.   

Exploring the limits of spin transport efficiency for spin ejection in spin photodiodes

We examine several factors that affect the efficiency of the transport of optically excited, spin-polarized carriers in ferromagnet-semiconductor heterostructures. The process of optical excitation leads to the creation of the population of spin carriers in a III-V semiconductor [1], which faces a number of obstacles on its way out of the semiconductor. This poster addresses a hierarchy of problems that need to be addressed in order to improve the efficiency of spin ejection, with the goal of bringing it up to the efficiency level of the opposite process, the spin injection. Our approach is based on modeling the existing spin ejection data, in order to understand several spin relaxation processes and the transport across the interface between a semiconductor and a ferromagnet or other metal. Our results are based in part on Schokley-Queisser [2] approach for photodiodes efficiency. Our investigation shows that there is a considerable space for improvement of spin ejection transport efficiency, which opens up possibility of designing novel spintronics devices. \\[4pt] [1] A. F. Isakovic, D. M. Carr, J. Strand, \textit{et al}., Phys. Rev. B \textbf{64} 161304.\\[0pt] [2] W. Schokley, H. J. Queisser, J. Appl. Phys. 32 (3), 510.   

Testing of Unfolding Algorithm Using Blind Data

The RooUnfold package currently has available several different algorithms for the numerical solution of inverse problems or unfolding. Time-dependent Regularized Unfolding for Economics and Engineering, also known as TRUEE is an algorithm used to unfold and with time will be integrated to the RooUnfold package. Tests using simulated data in TRUEE were made with the goal to let future users know which parameters are ideal for their data. To test the TRUEE algorithm we used simulated data, with a known distribution and two different resolutions. The number of degrees of freedom and knots were found for different bin sizes. Chi square was then used to compare the unfolded and real distribution. The bin sizes with the smallest chi square were then used to unfold the blind data along with its parameters. Smaller bin sizes were used as well and then re-binned to see if the distributions matched. These re-binned distributions matched the unfolded distribution but did not match the known distribution.   

Reconfiguration of the Receiver System for Sodium Doppler Wind/Temperature Lidar

The newly established USU Na Lidar has the capability to measure neutral temperature and horizontal winds in the mesopause region (80-110 km in altitude) under clear sky condition in full diurnal cycle. Current system setup allows the observations of zonal (east-west) and meridional (north-south) winds, but lacks the coverage of the wind speed in zenith direction, which is essential to estimate the vertical wind perturbations. Since such perturbations are most likely associated with the atmospheric gravity waves (bouncy waves) breaking events and the related energy, momentum transfer, this upgrade of the Na Lidar system will provide further detailed information to the ongoing studies of such gravity wave dynamics and the induced atmospheric instabilities in the MLT (mesosphere and lower thermosphere) region. The proposed addition of the fourth channel and the associated new design of the Lidar receiving system will not only enable the data acquisition of the zenith channel but, the same time, will produce a more compact and robust structure than the current design. The new design will accommodate four high quantum efficiency(40{\%}) Hamamatsu PMTs in the Lidar receiver, therefore, increase the system signal/noise(S/N) ratio by a factor of two.   

Surface adhesion and confinement variation of Escherichia coli on SAM surfaces

Controlled surface adhesion of non - pathogenic gram negative bacterial strain, Escherichia coli, DH5 alpha is interesting as a model system due to possible development of respective biosensors for prevention and detection of the pathogenic strain Escherichia coli and further as a study in biological and monolayer interactions. Self Assembled Monolayers (SAM) with engineered surfaces of linear thiols on Au(111) were used as the substrate. Sub cultured E. coli were used for the analysis. The SAM layered surfaces were dipped in varying concentrations of 2 -- 4 Log/ml E. coli solutions. Subsequent surface adhesion at different bacterial dilutions on surfaces will be discussed, and correlated with quantitative and qualitative adhesion properties of bacteria on the engineered SAM surfaces. The bacteria adhered SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).   

Aligned Single-Walled Carbon Nanotube Cantilevers

Researchers are striving to make smaller cantilever sensors with higher resonant frequencies in an effort to enhance force, position and mass detection sensitivity. With its minimal mass and high Young's modulus, a single wall carbon nanotube (SWNT) cantilever is suggested to represent the ultimate limit of this trend. We will present a novel nanolithography method that has been developed utilizing highly aligned SWNT's grown via chemical vapor deposition which are then transferred to a silicon/silicon dioxide substrate planarized with chemical mechanical polishing. This method allows us to create arrays of $\sim $ 1 nanometer diameter aligned SWNT cantilevers of tunable length (typically 75 to 700 nanometers) with densities on the order of one cantilever per micrometer. Details about the nanofabrication process analyzed via imaging techniques such as scanning electron microscopy and atomic force microscopy will be discussed. Our future work will include characterization of the mechanical properties of these cantilevers and possible applications in biological sensing.   

Parallel Performance Analysis between Free Response Environments and the Force Concept Inventory in Introductory Mechanics Courses

This paper reports our attempts to: 1) find a way to model and predict common thought processes that cause typical misconceptions identified by the Force Concept Inventory (FCI), 2) create a problem solving situation that folds in both kinematics and force discussions, and 3) accurately assess the students' ability to interpret a kinematic graph. Two pen and paper test questions were designed with these goals in mind, both broken into specific elements, not only to allow for partial credit, but also to arrive at a quantifiable fragmentation of the necessary thought processes required to solve the problem. These results were compared to pre- and post-FCI data to analyze the common misconceptions as defined by FCI and their correlation to mistakes in the thought processes in answering the designed questions. Ultimately this, and any future questions, would become a tool in the classroom to pinpoint the critical ideas with which a typical student struggles during a mechanics course.   

Surface engineering and adhesion modification of SAM surfaces of 1-mercaptoundecanoic acid 1-undecanethiol: confining Bacillus subtilis

Engineering surfaces for adhesion and confinement of bacteria is interesting towards development of respective biosensors, and to understand the interactions between biological systems and molecular layers. Investigation was focused on modification of surfaces towards confinement and entrapment of the nonpathogenic strain Bacillus subtilis or Bacillus pathogenic/non pathogenic variants and to study surface engineering. Clean, flat Au(111) on mica surfaces were used for self assembly for Self Assembled Monolayers (SAM). 1-mercaptoundecanoic acid and 1-undecanethiol were used at total 5 mM solutions in varying ratios, in 200 proof Ethanol solution. Resulting SAM layers were investigated for surface corrugation, morphology and structure variation at different thiol ratios. Observations will be discussed, quantitatively and qualitatively. Eventual mixture ratios were so selected towards optimum conditions for confining Bacillus subtilis as a model system. SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).   

Light Scattering Characterization of Salt Dependent Thermoreversible Micelles Synthesized from Elastin-Like Polypeptides

Environmentally responsive nanoparticles synthesized from Elastin-Like Polypeptides (ELP) present a promising system for applications such as biosensors, drug delivery vehicles, and viscosity modifiers. These nanoparticles undergo a transition from a soluble state at T$_{room}$ to micellar aggregates above the transition. The ELP micelles have been found to be sensitive to various outside stimuli including pH, salt concentration, and solvent. Dynamic and Static Light Scattering were used to study structure and dynamics of ELP nanoparticles below the transition and of formed ELP micelles above the transition. Micelles were found to generally depend strongly on solution pH, however, in the pH window of 10.1-10.4 their size stayed constant. The apparent radius and molecular weight of micelles in this pH range strongly depend on salt concentration with three apparent regimes. At low salt (0-15mM), largely spherical micelles were found with Rh=15nm, which corresponds to the size of folded ELP hydrophilic tail; and molecular weight of 5000-6000kg/mol. At the intermediate salt (15-30mM) the observed particles are spherical micelles that increase in size (by about 3 fold) and molecular weight (by about 50 fold) as salt concentration increases. At high salt concentrations (30-60mM), R$_{g}$/R$_{h}\sim $ 1.3, indicating the micelles behave as elongated particles with R$_{h}\sim $75nm that corresponds to the size of a stretched ELP chain with an apparent molecular weight of 300000-600000kg/mol.   

Fluorescence studies of gram-positive and gram-negative bacteria

Autofluorescence is a relatively unexplored technique for identification. It is nondestructive, noncontact, fast, and has the potential to be integrated in small handheld devices. On the other hand, the autofluorescent signal is sometimes very week, or it can be overwhelmed by the emission of a surrounding medium. We are exploring the possibility to develop an optical method for identification of the Gram-type of bacterial cultures based on the autofluorescence. We have enhanced the detectivity of a standard fluorimeter using combination of bandpass and long pass filters. In this particular study, we are investigating if the previously observed difference in the autofluorescent spectra of Gram-positive and Gram-negative bacteria is dependent on the age of the culture. We have selected two types of bacteria, Kocuria rhizophila and Alcagenes faecalis, and we have monitored in equal time intervals of their development the autofluorescence spectra. The stages of development were monitored separately by measuring the turbidity and creating a growth curve. The goal of this study is to find out if the previously observed difference in the autofluorescence spectra of Gram-positive and Gram-negative bacteria is dependent on the stage of the development of the bacterial culture.   

Surface engineering and adhesion modification of SAM surfaces of 1-dodecanethiol, and 3-mercapto-1-propanol: confining Escherichia coli

Engineering surfaces for adhesion and confinement of bacteria is interesting towards development of respective biosensors, and correlation of biological systems and molecular layers. Investigation was focused towards modification of surfaces towards confinement and entrapment of the nonpathogenic strain Escherichia coli or similar pathogenic strains and to study surface engineering. Clean, flat Au(111) on mica surfaces were used for self assembly for Self Assembled Monolayers (SAM). 1-dodecanethiol, and 3-mercapto-1-propanol were used at total 5 mM solutions in varying ratios, in 200 proof Ethanol solution. Resulting SAM layers were investigated for surface corrugation, morphology and structure variation at different thiol ratios. Observations will be discussed, quantitatively and qualitatively. Eventual mixture ratios were so selected towards optimum conditions for confining Escherichia coli as a model system. SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).   

Surface adhesion and confinement variation of Staphylococcus aurius on SAM surfaces

Controlled surface adhesion of non - pathogenic gram positive strain, Staphylococcus aureus is interesting as a model system due to possible development of respective biosensors for prevention and detection of the pathogenic strain methicillin resistant Staphylococcus aureus (MRSA) and further as a study for bio-machine interfacing. Self Assembled Monolayers (SAM) with engineered surfaces of linear thiols on Au(111) were used as the substrate. Sub cultured S. aureus were used for the analysis. The SAM layered surfaces were dipped in 2 -- 4 Log/ml S. aureus solution. Subsequent surface adhesion at different bacterial dilutions on surfaces will be discussed, and correlated with quantitative and qualitative adhesion properties of bacteria on the engineered SAM surfaces. The bacteria adhered SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).   

Precipitant diffusion and surface segregation in Al Alloys near melting point: Al 2024

Industrial Al alloys are precipitant hardened with an impurity phase. Micro precipitants introduce various novel physical properties to the systems system. The diffusion of these constituents under thermal gradient was studied by sequentially increasing temperatures near melting point as it was observed to better facilitate the migration of precipitants. Study is based on Al 2024, age hardened, high strength AL alloy, annealed at incremental temperatures near melting point of 500 C and was observed in Scanning Electron Microscopy (SEM) and Energy Dispersive X ray Spectroscopy (EDX). Solvent cleaned near surface region of the alloy was investigated with observation of differential migration of constituent Cu, Fe Mg and Zn precipitants. The migrations were modeled in terms of diffusion coefficients and established literature of the participating species. Study will attempt to correlate the elemental concentration variation with applied elevated heat stress in industrial settings.   

Entanglement in Quantum Harmonic Chains

We study interparticle entanglement in finite chains of coupled harmonic oscillators as a function of the vibrational mode, excitation number, and bipartition of oscillators. Harmonic chains are used as a model in quantum information theory for ion traps and simple solid state systems, and our results extend previous work for the Gaussian ground state to excited states. Entanglement is analyzed by calculating the purity of the reduced density matrix of the combined wavefunctions of the oscillators in the chain tracing, over subensembles. We present analytic and numerical results for a varying effective spring constants between the particles and number of particles in the chain. Our entanglement results show interesting correlations between the symmetries of the modes and the symmetries of the partitions.   

Computational Design of Druglike Small Molecule Plk1 PBD Inhibitors

Polo-like Kinase 1 (Plk1) participates in regulation of the cell cycle and is often overexpressed in cancers. Inhibition of Plk1 was found to suppress cancer development. Most known kinase inhibitors interact with highly conserved ATP binding sites of the kinases. This makes the design of Plk1-specific inhibitors difficult. However, Plk1 has another active site, the Polo-Box Domain (PBD). PBD is not present in other kinases that were studied here. In this research, the PBD site of Plk1 was used as a target for designing small molecules that could potentially bind Plk1. A previously designed small molecule, Purpurogallin (PPG), was found to bind only the PBD of Plk1 and a highly similar site of LYN kinase, but no other kinases. The PPG structure was used as a template to design new putative Plk1-specific inhibitors. Druglike properties of the new molecules were evaluated with the Osiris Property Explorer program. Interactions of the molecules with Plk1, LYN, and eight other kinases were studied using the Argus Lab docking program. Further search for Plk1-specific inhibitors that could potentially target cancers with overexpressed Plk1 is discussed.   

Experimental and Numerical Study of the Role of Disorder on Contact Angle Hysteresis

Hysteretic behavior of the contact angle of a liquid on a solid is often ascribed to topographic or chemical heterogeneity of the surface. Recent experiments by Rolley and Guthmann\footnote{E. Rolley and C. Guthmann, {\it Phys. Rev. Lett.} {\bf 98}, 166105 (2007).} on liquid hydrogen on cesium suggest that both the hysteresis and the contact line dynamics might be explained in terms of the mesoscale structure of the cesium surface. We have investigated a room temperature system with similar wetting and structural properties, tetradecane on dodecanethiol-treated evaporated gold films, and compare the results with a model of the expected hysteresis due to the topographical heterogeneity as measured by AFM, and reported disorder in the thiol film.\footnote{E. Delamarche, B. Michel, H. Kang and C.Gerber, {\it Langmuir} {\bf 10}, 4103 (1994).}   

Surface adhesion and confinement variation of Bacillus subtilis on SAM surfaces

Controlled surface adhesion of non - pathogenic gram positive strain, Bacillus subtilis is interesting as a model system due to possible development of respective biosensors for prevention and detection of the pathogenic variants B. anthracis and B. cereus. Further as a study for bio-machine interfacing systems. Self Assembled Monolayers (SAM) with engineered surfaces of linear thiols on Au(111) were used as the substrate. Sub cultured B. subtilis were used for the analysis. The SAM layered surfaces were dipped in 2 -- 5 Log/ml B. subtilis solution. Subsequent surface adhesion at different bacterial dilutions on surfaces will be discussed, and correlated with quantitative and qualitative adhesion properties of bacteria on the engineered SAM surfaces. The bacteria adhered SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).   

Micromechanical and structural study of ambient grown Au nanostructures on P doped Si(100)

Au nanostructure have wide application potential due to their noble nature, plasmonic, catalytic and specific conductive properties. Such nanostructures grown on substrate support under ambient conditions are complex but provides unique opportunities in dirty systems. In this model system Au was self assembled on solvent cleaned P doped Si(100) surface giving rise to near spherical geometry. Self assembly was initiated by magnetron sputter deposited Au at RT (300K) under high vacuum, on Si(100) which subsequently exposed to atmosphere. The micromechanical properties of the structures were measured by contact mode force curves in Atomic Force Microscopy (AFM). Both the stiffness and young modulus was measured for the nanostructures assembled and annealed at different temperatures. Initial plasticity of the nano structures was observed to reduce at annealing. Au nano structures were likely Stranski - Krastanov growth mode. Observed structure and their variations when annealed at successively higher temperatures will also be discussed. All measurements were taken by the AFM in contact intermittent contact and non-contact modes.   

Open-frame external cavity diode laser for teaching and research

We have constructed an open-frame, low-power, tunable external cavity diode laser suitable for both teaching and research purposes. We adapt the design of [1, 2] to an open, 4-rod frame composed entirely of commercially available parts. The laser can be quickly disassembled and reassembled by undergraduate students, while its open architecture provides an intuitive demonstration for students learning about laser physics. The laser will be used for atomic absorption spectroscopy. \\[4pt] [1] X. Baillard, et al., \textit{Opt. Comm.} \textbf{266}, 609 (2006) \\[0pt] [2] M. Gilowski, et al., \textit{Opt. Comm.} \textbf{280}, 443 (2007)   

Surface engineering and adhesion modification of SAM surfaces of 1-hexanethiol and 1-decanethiol: confining Staphylococcus aureus

Engineering surfaces for adhesion and confinement of bacteria is interesting towards development of respective biosensors, and bio machine interfacing. Investigation was focused towards modification of surfaces towards confinement and entrapment of the nonpathogenic strain Staphylococcus aureus or similar pathogenic strains and to study surface engineering. Clean, flat Au(111) on mica surfaces were used for self assembly for Self Assembled Monolayers (SAM). 1-hexanethiol, and 1-decanethiol were used at total 5 mM solutions in varying ratios, in 200 proof Ethanol solution. Resulting SAM layers were investigated for surface corrugation, morphology and structure variation at different thiol ratios. Observations will be discussed, quantitatively and qualitatively. Eventual mixture ratios were so selected towards optimum conditions for confining Staphylococcus aureus as a model system. SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).   

Scanning electron microscopy studies of bacterial cultures

Scanning electron microscopy is a powerful tool to study the morphology of bacteria. We have used conventional scanning electron microscope to follow the modification of the bacterial morphology over the course of the bacterial growth cycle. The bacteria were fixed in vapors of Glutaraldehyde and ruthenium oxide applied in sequence. A gold film of about 5 nm was deposited on top of the samples to avoid charging and to enhance the contrast. We have selected two types of bacteria Alcaligenes faecalis and Kocuria rhizophila. Their development was carefully monitored and samples were taken for imaging in equal time intervals during their cultivation. These studies are supporting our efforts to develop an optical method for identification of the Gram-type of bacterial cultures.   

Electrical Characterization of Temperature Dependent Resistive Switching in Pr$_{0.7}$C$_{0.3}$MnO$_{3}$

Resistive switching offers a non-volatile and reversible means to possibly create a more physically compact yet larger access capacity in memory technology. While there has been a great deal of research conducted on this electrical property in oxide materials, there is still more to be learned about this at both high voltage pulsing and cryogenic temperatures. In this work, the electrical properties of a PCMO-metal interface switch were examined after application of voltage pulsing varying from 100 V to 1000 V and at temperatures starting at 293 K and lowered to 80 K. What was discovered was that below temperatures of 150 K, the resistive switching began to decrease across all voltage pulsing and that at all temperatures before this cessation, the change in resistive switching increased with higher voltage pulsing. We suggest that a variable density of charge traps at the interface is a likely mechanism, and work continues to extract more details.   

Preparation and Characterization of C-16 and C-10 Fluorescent Dipyrrinone Liquid Crystal Langmuir-Blodgett Films

A new C-16 and C-10 Fluorescent Dipyrrinone Liquid Crystal has been synthesized by the University of West Florida's Chemistry department. The liquid crystals have amphiphilic properties with their dipyrrinone polar heads and long hydrocarbon nonpolar tails. This led to the preparation and characterization of their Langmuir and Langmuir-Blodgett Film, using a Nima Langmuir-Blodgett Trough. The influence of the length of the hydrocarbon tail on the behavior of the pressure-area isotherm of the Langmuir film is studied. There is considerable difference in the behavior of the C-16 and C-10 Fluorescent Dipyrrinone Liquid Crystal Films prepared. Ellipsometric characterization of the films, using an ellipsometer built by the Physics department, is used to further study the Liquid Crystal films.   

Characterization of Acryl amide Resins Using Static Light Scattering

Our research is based on the use of light scattering technique for the characterization of known and unknown particles within a liquid. The research focused specifically on the detection of resin polymer that may be present in the given samples using static light scattering. The sample was delivered into a high performance liquid chromatography system with static light scattering, refractive index and viscosity detectors. Static Light scattering measures the intensity of the light scattered as the function of scattering angle and polymer sample concentration. Based on these results the molecular weight and radius of gyration of the given sample can be calculated.   

Synthesis and properties of a new superconducting compound (ZrNixS2)

Since the discovery of superconductivity in chalcogenides in Fe-Se system and in iron pnictides much attention have been give for synthesis of new materials which can exhibit superconductivity. Within this context in this work we show results which suggest that ZrNi$_{x}$S$_{2}$, where x can assume 0.3, 0.5 and 0.8 values, is a new superconductor material. This compound crystallizes in a new crystallographic structure with hexagonal symmetry belongs to the space group R -- 32/m. Indeed this compound is a variation of the Zr$_{3}$S$_{4}$ which can be considered as the prototype structure of this new compound (ZrNi$_{x}$S$_{2}$). In this prototype structure zirconium atoms may occupy two different sites in the structure. Thus, nickel atoms substitute zirconium in a specific site of the structure. These results suggest that superconducting critical temperature is dependent of the nickel content in this new compound. The optimum Ni content yield to T$_{c}$ $\sim$ 9.8 K.   

Superconductivity in the T$_{2}$ phase of the Ta-Ge-B system

In the Ta-Ge system the $\alpha$Ta$_{5}$Ge$_{3}$ phase is not superconductor. Considering the high solubility of this phase for boron, in this work it has been evaluated the effect of boron doping in $\alpha$Ta$_{5}$Ge$_{3}$ on the electrical, heat capacity and magnetic properties of the produced materials. It has been shown that boron doping promoted superconductivity for some specific composition. The Ta$_{5}$GeB$_{2}$, also named T$_{2}$ phase, crystallizes in the tetragonal symmetry with Cr$_{5}$B$_{3}$ prototype structure. In this composition the sample presented the maximum superconducting critical temperature (3.4 K). Others systems that exhibit the existence of the T$_{2}$ phase present superconductivity such as Mo$_{5}$SiB$_{2}$ (T$_{c}$ $\sim$5.5 K), Nb$_{5}$Si$_{3-x}$B$_{x}$ (T$_{cmax}$ $\sim$7.8 K) and W$_{5}$SiB$_{2}$ (T$_{c}$ $\sim$5.5 K). Thus, Ta$_{5}$GeB$_{2}$ is more one example.   

Evidence of the superconductivity in the Zr-Pt-Te system

Layered transition metal dichalcogenides MetalX$_{2}$ are well-known CDW conductors, with low dimensionality properties. The structure of layered TMDC can be regarded as a stacking of covalent coupled M-X-X sandwiches, and the coupling between layers X-X is of weak van de Waals type. The intercalation of metallic atoms into the weak coupled region between the X-X layers leads to significant modification of electronic properties. In this work results suggest that the Pt intercalation is able for induce superconductivity in the matrix compound (ZrTe$_{2})$. The critical temperature at 6.5 K is revealed through of magnetization, resistivity and specific heat measurements. Heat-capacity measurements show unambiguously a bulk superconductivity behavior. However, the x-ray diffraction results reveal that ZrPt$_{x}$Te$_{2 }$can crystallize in the LiCrS2 prototype structure. Thus, we had shown that the superconductivity is induced by intercalation of Pt atoms.   

Superconductivity in Zr1-xVxB2

Since the discovery of superconductivity in MgB$_{2}$, much attention has been give for research in new diboride with potential for exhibit superconductivity. There are many diboride of refractory metals which crystallize in the same prototype structure than MgB$_{2}$ (AlB$_{2}$ prototype structure). However, only NbB$_{2}$ can exhibit superconductivity with superconductor critical temperature close to 3.5 K on the optimum composition. Some authors have been reported superconductivity in ZrB$_{2}$ with critical temperature close to 5.5 K, but this result was not reproduced for other research groups. In this work we present results which show that small substitution of Zr by V in the Zr$_{1-}$xVxB$_{2}$ is able for induce superconductivity in the matrix phase (ZrB$_{2}$). The best composition gives a superconducting critical temperature close to 8.5 K.   

Superconductivity in ZrVGe and HfVGe compounds

In the Zr-V-Ge and Hf-V-Ge there are two ternary phases of ZrVGe and HfVGe compositions which crystallize in a tetragonal symmetry. Both structures crystallize in the UGeTe prototype with space group I4/mmm. The lattice parameters of the two compounds are a = 3.72 {\AA} and c = 14.34 {\AA} for HfVGe and a = 3.75 {\AA} and c = 14.48 {\AA} for ZrVGe. In this structure the elements are arranged in layers in which obey V-RM-Ge sequence, where RM represents the refractory metal like Zr or Hf. In this work we show that both compounds are bulk superconductor with superconducting critical temperature at 4.8 K for HfVGe and 6.0 for ZrVGe.   

Superconductivity in ZrAgxTe2

Layered transition metal dichalcogenides of the type MX$_{2}$ (M is transition metal, X = S, Se, Te) have been studied for their electronic properties due to low dimensionality. In these materials each layer correspond to the hexagonal transition metal intercalated by two similar chalcogen sheets. In ZrTe$_{2}$ the prototype structure is CdI$_{2}$. The interaction of layers is weak as van der Walls bonding between chalcogen element (X). In general charge density wave and superconductivity coexist in these of materials. Indeed, various compounds of this material class exhibits this coexistence such as 2H-TaS$_{2}$, 2H-NbS$_{2}$ etc. Some results reported in literature about the electrical properties of ZrTe$_{2}$ show that this material presents metallic behavior at a temperature interval from 4.0 K to 300 K. In this work we present results about intercalation of silver in the ZrTe2 compound. The results suggest that the intercalation of Ag also is able to induce superconductivity in this compound. The superconducting critical temperature close to 9.0 K is revealed through of magnetization and resistivity measurements. The x-ray result reveals a new compound, originating from Ag intercalation and crystallizes in the LiCrS$_{2}$ prototype structure.   

Superconductivity in ZrCuxTe2

Layered transition metal dichalcogenides of the type MX$_{2}$ (M is transition metal, X = S, Se, Te) have been studied for their electronic properties due to low dimensionality. In these materials each layer correspond to the hexagonal transition metal intercalated by two similar chalcogen sheets. In ZrTe$_{2}$ the prototype structure is CdI$_{2}$. The interaction of layers is weak as van der Walls bonding between chalcogen element (X). In general charge density wave and superconductivity coexist in these of materials. Indeed, various compounds of this material class exhibits this coexistence such as 2H-TaS$_{2}$, 2H-NbS$_{2}$ etc. Some results reported in literature about the electrical properties of ZrTe$_{2}$ show that this material presents metallic behavior at a temperature interval from 4.0 K to 300 K. Thus, in this work we present results about intercalation of Cu in the ZrTe2 compound. The results suggest that the intercalation of Cu is able to induce superconductivity in this compound. The superconducting critical temperature close to 10.2 K is revealed through of magnetization and resistivity measurements. The x-ray result reveals a new compound, originating from Cu intercalation and crystallizes in the LiCrS$_{2}$ prototype structure.   

Synthesis and properties of a new superconducting compound (ZrCuxSe2)

Since the discovery of superconductivity in chalcogenides in Fe-Se system and in iron pnictides much attention have been give for synthesis of new materials which can exhibit superconductivity. Within this context in this work we show results which suggest the existence of a new selenite intercalate with copper atoms in the ZrCu$_{x}$Se$_{2}$ nominal composition, where x is 0.1 $\leq{}$ x $\leq{}$ 0.4 interval. A superconductor behavior begins in the ZrCu$_{0.3}$Se$_{2}$ with superconducting critical temperature close to 9.0 K. ZrSe$_{2}$ is a compound which crystallize in the hexagonal symmetry with CdI$_{2}$ prototype structure belongs to the space group P-32/m1. Indeed, copper is intercalating between Se-Se which have van der Walls interaction in the ZrSe$_{2}$ compound. This intercalation with copper atoms, produce superconductivity in the matrix compound (ZrSe$_{2}$) which is not superconductor. The copper intercalation in the matrix compound crystallizes in a LiCrS$_{2}$ prototype structure.   

Superconductivity in a new compound of Zr2CuSb3 composition

In the Zr-Cu-Sb system there is a phase of Zr$_{2}$CuSb$_{3}$ composition which represents a ternary compound. This phase crystallize in a new prototype structure Zr$_{2}$CuSb$_{3}$ which have a tetragonal symmetry with space group P-4m2. The lattice parameters are a=3.9404 {\AA} and c=8.6971 {\AA}. This structure can be represented as sequence of 1Zr.4Sb.2Cu.2Sb and (4Sb) which form like layer compound. However, the literature is very poor in results about the properties of this compound. Thus, in this work we show results which suggest the existence of superconductivity with superconducting critical temperature close to 8.0 K. These conclusions were obtained through X-ray diffraction, magnetization, and resistivity measurements.   

Microscopic description of vortices in nanoscale superconductors

The results of Bogolyubov-de-Gennes calculations for thin superconducting discs and squares in applied magnetic field will be presented. The paramagnetic effect is taken fully into account. The vortex phase diagrams for the samples of nanoscopic size will be constructed and compared with the predictions of the Ginzburg-Landau theory. The size limitations for the entering of one and several vortices as function of material parameters will be established. Several unusual vortex transformations during the vortex pattern evolutions as function of temperature and field will be discussed.   

Hexagonal pnictide SrPtAs; the role of spin-orbit interaction and locally broken inversion symmetry

The first hexagonal pnictide superconductor SrPtAs which consists of stacked PtAs layers has been studied using the FLAPW method\footnote{Wimmer, Krakauer, Weinert, and Freeman, Phys.Rev.B. {\bf 24}, 864 (1981)} and tight-binding methods. The single PtAs layer forms a honeycomb structure that exhibits: (1) locally broken inversion symmetry despite the presence of the global inversion center, and (2) strong spin-orbit interaction, for which physical consequences are nontrivial. Based on these findings, we predict significant enhancement of both the spin susceptibility and the paramagnetic limiting field with respect to the usual {\em s} wave superconductors. Further, we suggest an increase of $T_C$ by electron doping of a van Hove singularity.   

Superconductivity and structural variation of the electron-correlated layer systems Sr(Pd$_{1-x}T_x$)$_2$Ge$_2$ ($T$ = Co, Ni, or Rh; $0 \leq x \leq 1$)

Superconductivity variations in the pseudoternary Sr(Pd$_{1-x}T_x$)$_2$Ge$_2$ layer system (Pd($4d^8$), $T$ = Co($3d^7$), Ni($3d^8$), or Rh($4d^7$); $0 \leq x \leq 1$) are reported. For the BaFe$_2$As$_2$-type tetragonal structure, the degenerate $nd^7$ or $nd^8$ orbital of transition metal $T$ is splitted by $c$-axis squeezed $T$Ge$_4$ tetrahedral crystal field in the $T$-Ge layer. For the isoelectronic Sr(Pd$_{1-x}$Ni$_x$)$_2$Ge$_2$ system, superconducting transition temperature $T_c$ decreases monotonically from 3.12 K for $4d$-band SrPd$_2$Ge$_2$ to 0.92 K for $3d$-band SrNi$_2$Ge$_2$, where major contribution of conduction electrons was from the half-filled dispersive 3D-like upper-lying $nd_{xz,yz}$ bands. For the Sr(Pd$_{1-x}$Rh$_x$)$_2$Ge$_2$ system, $T_c$ decreases to 2.40 K with 25\% of $4d^7$ Rh substitution. For the Sr(Pd$_{1-x}$Co$_x$)$_2$Ge$_2$ system, $T_c$ decreases sharply to 2.58 K with only 3\% of $3d^7$ Co substitution. The lower $T_c$ of the present electron-overdoped ($nd^7$ or $nd^8$) compound is due to dispersive 3D-like $nd_{xz,yz}$ conduction bands with weak electron correlation.   

Local antiferromagnetic exchange and collaborative Fermi surface as key ingredients of high temperature superconductors

Cuprates, ferropnictides and ferrochalcogenides are three classes of unconventional high-temperature superconductors, who share similar phase diagrams in which superconductivity develops after a magnetic order is suppressed, suggesting a strong interplay between superconductivity and magnetism, although the exact picture of this interplay remains elusive. Here we show that there is a direct bridge connecting antiferromagnetic exchange interactions determined in the parent compounds of these materials to the superconducting gap functions observed in the corresponding superconducting materials. High superconducting transition temperature is achieved when the Fermi surface topology matches the form factor of the pairing symmetry favored by local magnetic exchange interactions. Our result offers a principle guide to search for new high temperature superconductors. References: Jiangping Hu and Hong Ding, Arxiv:1107.1334 (2011)   

Electronic structure of iron-based superconductors from DFT+DMFT: the important role of Hund's coupling and correlations

The iron pnictide and chalcogenide compounds are a subject of intensive investigations due to their surprisingly high temperature superconductivity. Density functional theory (DFT) has been widely used in the theoretical study but often suffers from significant discrepancy with experimental observations. The fundamental reason is that the low energy electrons in many iron-based superconductors, while displaying nice Fermi-liquid behavior, form quasiparticles and acquire sizable masses. Thus the actual low energy electronic states are strongly renormalized compared to DFT bands. We show that the combination of DFT and dynamic mean field theory (DFT+DMFT), which incorporates the detail electronic structure and local electronic correlations, overcomes most of DFT limitations and describe well the trends in all the physical properties such as the ordered moments, effective masses, Fermi surfaces, x-ray spectroscopy, optical conductivity, magnetic excitations and so on across all families of iron-based compounds, and find them in good agreement with various different experiments. We stress that Hund's blocking mechanism and electronic correlations are crucial in determining the electronic structures of iron-based superconductors.   

Chlorine-doping effects on crystal structure and superconductivity in FeSe$_{1-x}$Cl$_{y}$

According to the assessed Fe-Se phase diagram,\footnote{``Binary Alloy Phase Diagrams'' 2$^{nd}$ edition, ASM International, Editor-in-Chief: Thaddeus B. Massalski, pp 1769-1770 (1992).} the FeSe compound could crystallize either in tetragonal Pb-O type structure with space group P4/nmm (called $\beta $ FeSe) or hexagonal Ni-As type structure with space group P6$_{3}$/mmc (called $\delta $ FeSe) depending on the materials preparation process. In general, different starting composition of FeSe$_{x}$ results in a mixture of superconducting phase with almost identical T$_{c}$ and different amounts of magnetic impurity, therefore, it was proposed that the tetragonal $\beta $-FeSe superconducting phase (T$_{c} \quad \sim $ 8 K) only exists in a very narrow Se-deficiency range.\footnote{Zhaofei Li, et. al., J. Phys. {\&} Chem. Solids, \textbf{71}, 495-498 (2010).} Our experimental data indicated that the single hexagonal $\delta $ phase sample could be obtained by carrying out the low-temperature (400 $^{\circ}$C) annealing for FeSe$_{x}$Cl$_{y}$ after reaction at 680 $^{\circ}$C. This result is contrary to what is observed in the FeSe system in which the tetragonal $\beta $ phase is the predominant stable one at the low annealing temperature 400 $^{\circ}$C. As compared with the $\beta $-FeSe superconductor reported in the literature, higher T$_{c}$ values ($>$ 8 K) and larger superconducting volume fraction could be achieved by suitable tuning and heat treatments in the FeSe$_{x}$Cl$_{y}$ system.   

Effective five band analysis on the lattice structure effect in iron pnictides

The discovery of superconductivity in the iron pnictides[1] and its $T_c$ up to 55K[2] has given great impact to the field of condensed matter physics. From the early stage, much attention has been paid to the correlation between $T_c$ and the lattice structure[3] . In the present study, we focus on the condition for optimizing superconductivity in the iron pnictides, varying hypothetically the lattice structure of LaFeAsO. Studying the band structure of the hypothetical lattice structure of LaFeAsO, the hole Fermi surface multiplicity is found to be maximized around the Fe-As-Fe bond angle regime where the arsenic atoms form a regular tetrahedron. Superconductivity is optimized within this three hole Fermi surface regime, thereby providing a natural explanation as to why $T_c$ is optimized around the regular tetrahedron angle. Combining also the effect of the varying the Fe-As bond length, we provide a guiding principle for obtaining high $T_c$. [1]Y.Kamihara {\it et al.}, J. Am. Chem. Soc. {\bf 130}, 3296 (2008). [2]Z-A Ren {\it et al.}, Chinese Phys. Lett. {\bf 25}, 2215 (2008). [3]C.H. Lee {\it et al.}, J. Phys. Soc. Jpn. {\bf 77}, 083704 (2008).   

The origin of the electron-hole asymmetry of the spin fluctuations and the effect on superconductivity in iron-based superconductors

Development of the spin fluctuation has been considered as one of the important features in the iron-based superconductors. One of interesting observation is the electron-hole asymmetry in its incommensurability, which appears in the neutron scattering experiments. In the present study, we study the origin of this electron-hole asymmetry, and its effect on the superconducting gap form. We first obtain a 10 orbital model for 122 iron-based superconductors from first principle calculation and obtain 5 orbital model in the unfolded Brillouin zone, which can only be done approximately in 122 systems. We apply the random phase approximation to these models to obtain the spin susceptibility, and solve the Eliashberg equation for the spin-fluctuation-mediated superconductivity. We find that the origin of the electron-hole asymmetry of the spin fluctuations is the multi-orbital nature of the Fermi surfaces. The multi-orbital nature of the Fermi surface is also found to be important in the appearance of horizontal nodes in the superconducting gap found found in the calculation for 122 systems.   

Re-entrant Resistance and Transport Anomalies in P-doped Eu Pnictide: EuFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$, with coexisting superconducting and ferromagnetic phases

The doping of Eu 122 pnictides by Phosphorus has been shown to result in superconductivity which coexists with ferromagnetism of spins ordered in Eu sites. Recently, in the course of exploring Fe-based superconductors, we observed both SC associated with Fe-3d electrons and ferromagnetism due to the long-range ordering of Eu-4f moments in EuFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$ and in similar compound with lower P-doping, at 0.27 the $R(T)$ peak appears at $T \sim $ 19 K [1]. This $R(T)$ peak is associated with suppression of superconductivity by ferromagnetism and a re-entrance of resistance at low temperature. This presentation further investigates the pnictides at different P doping levels with transport measurements, correlated with magnetic and ESR data. Pnictides were made with a Solid state reaction method including the flux method to grow the single crystals. The dependence of the transition temperature and the behavior of the re-entrant $R(T)$ peak at 18-19 K on magnetic field and amount of dopant are addressed. [1]Aamir Ahmed, M. Itou, Shenggao Xu, Zhu'an Xu, Guanghan Cao, Y. Sakurai, James Penner-Hahn, Aniruddha Deb, Phys. Rev. Letters 105, 207003 (2010)   

First principles Study on Transparent High-Tc Superconductivity in hole-doped Delafossite CuAlO2

The CuAlO$_2$ is the transparent $p$-type conductor without any intentional doping. Transparent superdoncutivity and high thermoelectric power are suggested in $p$-type CuAlO$_2$ [1]. Katayama-Yoshida {\it et al.} proposed that it may cause a strong electron-phonon interaction and a superconductivity. But, the calculation of superconducting critical temperature $T_{\rm c}$ is not performed. We performed the first principles calculation about the $T_{\rm c}$ of hole-doped CuAlO$_2$ by shifting the Fermi level rigidly. In lightly hole-doped CuAlO$_2$, the Fermi level is located at Cu and O anti-bonding band. The electrons of this band strongly interact with the A$_1$L$_1$ phonon mode because the direction of O-Cu-O dumbbell is parallel to the oscillation direction of the A$_1$L$_1$ phonon mode. As a result, $T_{\rm c}$ of lightly hole-doped CuAlO$_2$ is about 50 K. We also discuss the materials design to enhance the $T_{\rm c}$ based on the charge-excitation-induced negative effective $U$ system.\\[4pt] [1] H. Katayama-Yoshida, T. Koyanagi, H. Funashima, H. Harima, A. Yanase: Solid State Communication {\bf 126} (2003) 135. \\[0pt] [2] A. Nakanishi and H. Katayama-Yoshida: Solid State Communication, in printing. (arXiv:1107.2477v3   

Synthesis of the electron-doped copper superconductors Eu$_{2-x}$Ce$_{x}$CuO$_{4-y}$ and their physical property characterization using the X-ray powder diffraction and high pressure

The electron-doped copper superconductors Eu$_{2-x}$Ce$_{x}$CuO$_{4-y}$ (0 $\leq$ $x$ $\leq$ 0.25 ) were synthesized successfully using a solid state reaction method under a series of annealing and reduction procedures. X-ray diffraction and high hydrostatic pressure were used for their structure and electrical property characterization. Preliminary results show that the samples are in a single phase and the T$_{c}$ drops as the pressure increases with a rate in sign opposite to the hole-doped counterparts and in magnitude apparently smaller than other cuprate superconductors.   

Investigation of Un-reacted, Multi-phase, Solution-Derived Targets for Pulse Laser Deposition (PLD) of High T$_{c}$ Superconducting Y$_{2}$Ba$_{4}$Cu$_{8}$O$_{16}$ (Y248) In-Situ, Epitaxial Thin Films

Y$_{2}$Ba$_{4}$Cu$_{8}$O$_{16}$ (Y248) is known to be robust in terms of O stability and is characterized by the absence of twin formation, and no structural phase transitions. It is stable in ambient atmosphere, resisting H$_{2}$O (and possibly even CO$_{2}$ exposure). These characteristics make Y248 more attractive for several applications of thin film superconductors as compared to Y$_{1}$Ba$_{2}$Cu$_{3}$O$_{7-\delta }$ (Y123). In addition, Y248 is very likely to have a much lower 1/f electrical noise level than Y123. (Electrical noise in Y123 has been shown to arise from mobile O defects). This would be an important advantage, since it has been established that electrical noise is a performance limiting parameter for Y123 devices. Limited past work on Y248 films has shown that a traditional approach to the growth of thin films by PLD that use stoichiometric, fully reacted, single phase targets has not been successful in achieving in-situ, epitaxial Y248 films. Such studies have also indicated the potential for achieving in-situ, epitaxial, PLD Y248 films using an un-reacted, multi-phase, solution-derived target. We will present results of our work towards obtaining high quality, in-situ, epitaxial thin films of Y248 via PLD employing non-traditional targets.   

Superconductivity via Two-Phase Condensation of Localized Electrons

Superconductivity is believed to occur via the formation of bound Cooper pairs of charge 2$e$, and Bose condensation of the pairs. Recently, a fundamentally different approach [1] was developed that combines two novel aspects. First, a ``distortion lattice'' akin to an incommensurate dynamic charge-density wave is induced by the electron-phonon interaction. This localizes individual electrons on the scale of the coherence length by diffraction at the Brillouin zone of this distortion lattice, thus forming an energy gap. Second, these localized electrons are packed together with others of the same energy in two interlocked close-packed sublattices, analogous to ions in an ionic crystal. The electron wavefunctions in each sublattice are coherently in phase with each other, but out of phase with those in the other sublattice. The two sublattices together constitute a stable condensed structure compatible with the Pauli principle, which maintains long-range order of the quantum phase of the localized electrons. This structure can move coherently without pinning or resistance, manifesting itself as a supercurrent. Remarkably, the electron localization gap maps onto the BCS gap equation, and the flux quantum $h$/2$e$ is reproduced, without the presence of bound electron pairs. Moreover, this picture is easily extended to electron localization mediated by spin waves or other excitations. Experimental approaches to distinguish this new picture from conventional theories will be discussed. \\[4pt] [1] A.M. Kadin, http://arxiv.org/abs/0909.2901; http://arxiv.org/abs/1007.5340.   

Theory of High-$T_{C}$ Superconductivity: Accurate Predictions of $T_{C}$

The superconducting transition temperatures of high-$T_{C}$ compounds based on copper, iron, ruthenium and certain organic molecules is discovered to be dependent on bond lengths, ionic valences, and Coulomb coupling between electronic bands in adjacent, spatially separated layers [1]. Optimal transition temperature, denoted as $T_{C0}$, is given by the universal expression $k_{B} T_{C0}$ = $e^{2}\Lambda/\ell\zeta$; $\ell$ is the spacing between interacting charges within the layers, $\zeta$ is the distance between interacting layers and $\Lambda$ is a universal constant, equal to about twice the reduced electron Compton wavelength (suggesting that Compton scattering plays a role in pairing). Non-optimum compounds in which sample degradation is evident typically exhibit $T_{C}$ $<$ $T_{C0}$. For the 31+ optimum compounds tested, the theoretical and experimental $T_{C0}$ agree statistically to within $\pm$ 1.4 K. The elemental high-$T_{C}$ building block comprises two adjacent and spatially separated charge layers; the factor $e^{2}/\zeta$ arises from Coulomb forces between them. The theoretical charge structure representing a room-temperature superconductor is also presented. \\* 1. doi:10.1088/0953-8984/23/29/295701   

Two-orbital analysis on the material dependence of $T_c$ in the single-layered cuprates

The significant material dependence of $T_c$ in the cuprates remains an important puzzle, even within the single-layer family. A recent paper[1] has demonstrated, with a two-orbital model, that, while the usual wisdom is to considered the cuprate as a one-band ($d_{x^2-y^2}$) system, a hybridization with the second ($d_{z^2}$) one around the Fermi energy significantly affects $T_c$ in the spin-fluctuation mediated pairing. There, the energy offset ($\Delta E$) between the two orbitals has been shown to govern the extent of the $d_{z^2}$ mixture, hence $T_c$. Here we further extend this line of approach to identify the key factors that determine $\Delta E$ in the cuprates, focusing on the structural difference among broader (La, Hg, Bi, and Tl) single-layer cuprates. We have revealed that the apical oxygen height ($h_{\rm{O}}$) above the CuO$_2$ plane and the separation ($d$) between the CuO$_2$ planes are the important parameters that determine $\Delta E$, thereby causing the material dependence of $T_c$. This picture enables us to capture the $T_c$ variation among the single-layered cuprates in a simple lattice-parameter space. [1]H. Sakakibara {\it et al.} Phys. Rev. Lett. {\bf 105}, 057003 (2010)   

Specific heat of cuprate superconductors

We model cuprate superconductors as a fluid of electrons able to create pairs within an infinite layered structure. The paired electrons (Cooper pairs) coexist with the unpaired electrons in almost two dimensional slabs stacked in their perpendicular direction. Electron pairs are considered as noninteracting zero spin bosons with a linear dispersion relation, and inter-slab penetrable planes are simulated by Kronig-Penney delta potential taken in one dimension, while paired and unpaired electrons are free to move in the other two dimensions. We introduce the slab thickness and the plane ``impenetrability'', using real parameters of YBaCuO$_{7-x}$ cuprates. Paired electrons develop a boson condensate with a jump in the specific heat at the superconductor critical temperature. After summing the electronic contributions, paired plus unpaired, we obtain a linear behavior of the electronic specific heat over temperature, $C_e/T$. By adding the lattice specific heat (phonons) $C_{l}$, we are able to qualitatively reproduce the total specific heat. We also obtain a theoretical value for the electronic specific heat constant $\gamma_e$, which is in agreement with the experimental values reported.   

How to measure the spatial characteristics of the Kosterlitz- Thouless transition in disordered systems?

The effect of disorder on the Kosterlitz-Thouless (KT) transition in two dimensions is unresolved. Here we propose and simulate an experiment to probe the spatial nature of the KT transition in such disordered systems, by studying the effects of cutting individual bonds in the disordered classical two-dimensional XY model. This will allow, similar to experiments carried out on quasi one-dimensional and on quantum Hall systems, to probe the channels through which global phase coherence propagates. We analyze the spatial distribution of these bonds and discuss implications towards a percolation description of the KT transition in superconducting thin films.   

Determination of superconducting parameters of Gd-123 phase added with Co$_{2}$FeO$_{4}$ nano ferrite from Excess conductivity and magneto conductivity analysis

Excess conductivity and magneto conductivity data of the Gd-123 added with Co$_{2}$FeO$_{4}$ nano ferrite were analyzed in terms of Aslamazov--Larkin and Maki--Thompson models for layered superconductors. Co$_{2}$FeO$_{4}$ nano ferrite was prepared by Co-perceptions method with grain size of about 20 nm. The concentrations of Co$_{2}$FeO$_{4}$ nano ferrite were varied from 0.0 to 0.1 {\%} wt. of the total sample's weight. The superconducting parameters such as superconducting transition temperature, coherence lengths along \textit{ab-}plane and along $c$-direction at 0K and phase breaking time at 100 K were determined as a function of Co$_{2}$FeO$_{4}$ nano ferrite concentrations. The superconducting transition temperature decreased from 91.7 K to 79.3 K as Co$_{2}$FeO$_{4}$ nano ferrite concentrations increased from 0.0 to 0.1 {\%} wt. of the total sample's weight, confirming with the decrease of phase breaking time at 100 K from 2.7x10$^{-14}$ sec to 1.93x10$^{-14}$ sec. The superconducting anisotropy parameter was calculated as a function of Co$_{2}$FeO$_{4}$ nano ferrite concentrations and its value varied from 6.7 to 8.3.   

Magnetothermoelectric effects in Fe$_{1+d}$Te$_{1-x}$Se$_x$

We report data on resistivity as well as Hall, Seebeck and Nernst coefficients for the Fe$_{1+d}$Te$_{1-x}$Se$_x$ single crystals with $x$ = 0, 0.39, and 0.40. The parent compound $\rm Fe_{1.04}Te$ exhibits a Fermi surface reconstruction at $T$ = 61 K, which is ascribed to the onset of the antiferromagnetic order. Two very closely doped samples: $Fe_{1.01}Se_{0.39}Te_{0.61}$ (Se39) and $\rm Fe_{1.01}Se_{0.4}Te_{0.6}$ (Se40) are superconductors with $T_c$ = 13.4 K and 13.9 K, respectively. Properties of these two single crystals are almost identical at high temperatures, but start to diverge below $T \approx$ 80 K. Despite there is no magnetic transition in neither Se39 nor Se40, the observed differences seem to be a consequence of varying with selenium content spin correlations.   

Magnetism in EuBCO and YBCO vortex states near and below T$_{c}$

By means of MaxEnt-$\mu $SR [1] analysis, we investigate transverse field $\mu $SR data [2] of EuBa$_{2}$Cu$_{3}$O$_{7-\delta }{\rm g}$EuBCO; T$_{c}$ = 93 K). Our focus is on a temperature interval near T$_{c }$to search for precursor effects, [3] and for predicted [4a] pseudogap loop currents above \textit{and} below T$_{c}$, already observed [4b] above T$_{c}$ for GdBCO. Further, we continue to study the field-direction dependence of the predicted [5a] and observed [5b] antiferromagnetism (AF) below 0.5T$_{c}$ for the vortex states in c-axis-oriented YBCO. This AF in and near the vortex cores is likely three-dimensional. In sum, magnetic roots of cuprate superconductivity are well plausible. Research is supported by LANL-DOE, REU-NSF and AFC. \\[4pt] [1] C Boekema and MC Browne, AIP Conf Proc {\#}1073 (2008) 260.\\[0pt] [2] DW Cooke \textit{et al}, Phys Rev B 39 (1989) 2748.\\[0pt] [3] B Aguilar, C Boekema \textit{et al}, Bull Am Phys Soc 37 (1992).\\[0pt] [4a] CM Varma, Phys Rev Lett 83 (1999) 3538.\\[0pt] [4b] T Songatikamas \textit{et al}, J Supercond {\&} Novel Magn 23 (2010) 793.\\[0pt] [5a] S-C Zhang, Science 275 (1997) 1089; H-D Chen \textit{et al}, Phys Rev B70 (2004) 024516.\\[0pt] [5b] C. Boekema \textit{et al}, J Phys Conf Series, 150 (2009) 052022. http://jpcs.iop.org/LT25   

Confinement induced anisotropy of superconducting films onto porous anodized aluminum oxide

We investigate the matching effect observed in superconducting Nb films sputtered on anodized aluminum oxide substrates containing regular arrays at various external magnetic field orientations. We find that both the magnetoresistance and the transition temperature exhibits two strong anisotropic effects: Little-Parks oscillations whose period varies with field direction superimposed on a smooth background arising from one dimensional confinement by the finite lateral space between neighboring holes, revealing the anisotropy change due to the confinement effect of artificial holes.   

Theoretical Study of Tunneling Conductance in Normal-Metal/Insulator/PrOs$_{4}$Sb$_{12}$ and Ferromagnet/Insulator/PrOs$_{4}$Sb$_{12}$ Junctions

We theoretically investigate the tunnel conductance in normal-metal/insulator/superconductor and ferromagnet/insulator/superconductor junctions for the unconventional superconductor PrOs$_{4}$Sb$_{12}$. Using several pair potentials provided by group theoretical considerations, the conductance is calculated for singlet as well as triplet pairing. The result shows that the direction of the electric tunneling current and the relative orientation of the superconductor (i.e. position of point nodes) are two main factors that determine the shape of conductance spectrum for a junction. In addition, comparison with experimental results provide useful information regarding the actual symmetry of the pair potential in the superconducting phase of PrOs$_{4}$Sb$_{12}$.   

Scattering from incipient stripe order in the high-temperature superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$

We use spectroscopic mapping with the scanning tunneling microscope to probe modulations of the electronic density of states in single crystals of the high temperature superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ as a function of temperature. We show that the Cu-O bond-oriented modulations, with periodicity near four lattice constants (4a), that form below the pseudogap temperature have a temperature-dependent energy dispersion displaying different behaviors in the superconducting and pseudogap states. We demonstrate that quasiparticle scattering off impurities does not capture the experimentally observed energy- and temperature-dependence of these modulations. Instead, a model of scattering of quasiparticles from short-range stripe order is necessary to reproduce the experimentally observed energy dispersion of the bond-oriented modulations and its temperature dependence across the superconducting critical temperature, T$_{c}$.   

STM/STS Study of Li$_x$CoO$_2$ Single Crystals

We have performed low temperature scanning tunneling microscopy/spectroscopy (STM/STS) measurements on Li$_x$CoO$_2$ (x=0.66) single crystal surfaces. A (1x1) hexagonal lattice was clearly observed and found to be moved by changing bias-voltage polarity, indicating that this could be associated with Li ions on the surface. Under the (1x1) hexagonal lattice, we imaged almost randomly distributed bright dots that were strongly dependent on bias-voltage, with insulating spectroscopic features. Different area on the surface showed a (2x2) hexagonal lattice that could be related to an ordering of Co$^{3+}$ and Co$^{4+}$ ions. These results suggest the electronic structure of Li$_x$CoO$_2$ surface is inhomogeneous possibly due to segregation of Li ions.   

Scanning tunneling microscopy at 70 mK in the dichalcogenide superconductor $TaSe_2$

We present scanning tunneling microscopy and spectroscopy measurements of the layered dichalcogenide $2H$-$TaSe_2$, performed in a dilution refrigerator cryostat equipped with a three axis superconducting magnet. In this compound superconductivity and charge density wave (CDW) ordering coexist below $200mK$. We find CDW order corresponding to hexagonal ($2H$) symmetry, but we also find areas where CDW order corresponding to trigonal ($1T$) symmetry appears. We study the superconducting density of states as a function of position and magnetic field at $70mK$ and relate the results to the CDW patterns.   

Long-Range Superharmonic Josephson Current

We consider a long superconductor-ferromagnet-superconductor junction with one spin-active region. It is shown that an \textit{odd} number of Cooper pairs cannot have a long-range propagation when there is \textit{only one} spin-active region. When temperature is much lower than the Thouless energy, the coherent transport of \textit{two} Cooper pairs becomes dominant process and the \textit{superharmonic} current-phase relation is obtained ($I\propto\sin2\phi$).   

Ground Capacitance in Josephson Junction Arrays

Josephson junction arrays (JJAs) have gained popularity in modern experiments. They find employment as high impedance ``superinductance'' elements in fluxonium type qubits [Manucharyan et al. Science 326, 113 (2009)] or in the study of Bloch oscillation. However this high impedance behavior is limited at high frequencies by the junction array capacitance to ground. We investigate the dependence of JJAs impedance on frequency. The JJA behaves as a linear inductance for frequencies sufficiently bellow the array self resonance. The maximum number of junctions in the array is thus limited by the ground capacitance. We study the dependence of the ground capacitance of JJAs on their geometry, and extract general design principles which will reduce this parasitic coupling and maximize the number of junctions in the superinductance.   

Bias current effect on inverse spin-switch behavior in Permalloy/Nb/Permalloy trilayers

We investigated the effect of bias current on the inverse spin-switch (ISS) effect in Permalloy(Py)/Nb/Permalloy trilayers. Samples grown by using dc magnetron sputtering methods were patterned in the bar shape of 5 $\mu $m wide and 120 $\mu $m long, and their magnetoresistance (MR) in the superconducting transition region were measured in sweeping magnetic fields. The MR measured in the transition region of Nb at the antiparallel domain (AD) states of two outer Py layers showed a rapid increase compared to the MR at the parallel (P) states with increasing current density. At high enough bias current densities exceeding 10$^{5}$ A/cm$^{2}$, we found a temperature window where the MR at the AD states returned to the normal state resistance whereas the MR at the P state remained superconducting. This ideal ISS effect is assumed to be originated in massive flux flow triggered by the onset of flux motion inside Nb layer due to the large Lorentz force exerting on flux lines where the magnetic flux were induced by the normal component of the stray field from the domain walls in the AD state of Py layers.   

Thermal fluctuations and flux-tunable barrier in proximity Josephson junctions

The effect of thermal fluctuations in Josephson junctions is usually analysed using the Ambegaokar-Halperin (AH) theory in the context of thermal activation. We report measurements of micron-scale normal metal loops contacted with thin superconducting electrodes, where the unconventional loop geometry enables tuning of the junction barrier with applied flux. We observe stronger ``enhanced'' fluctuations when the flux threading the normal metal loop is near an odd half-integer flux quantum, and for devices with thinner superconducting electrodes. These findings suggest that the activation barrier, which is the Josephson coupling energy of the proximity junction, is different from that for conventional macroscopic Josephson junctions. Simple one dimensional quasiclassical theory is used to predict the interference effect due to the loop structure, but the exact magnitude of the coupling energy cannot be computed without taking into account the details of the sample dimensions. In this sense, the physics of nanoscale proximity junctions can be related to the thermally activated phase slips (TAPS) model for thin superconducting wires, and indeed our data can be better fitted with TAPS model than AH theory.   

Enhancement of shot noise due to the fluctuation of Coulomb interaction

We have developed a theoretical formalism to investigate the contribution of fluctuation of Coulomb interaction to the shot noise based on Keldysh non-equilibrium Green's function method. We have applied our theory to study the behavior of dc shot noise of atomic junctions using the method of nonequilibrium Green's function combined with the density functional theory (NEGF-DFT). In particular, for atomic carbon wire consisting 4 carbon atoms in contact with two Al(100) electrodes, first principles calculation within NEGF-DFT formalism shows a negative differential resistance (NDR) region in I-V curve at finite bias due to the effective band bottom of the Al lead. We have calculated the shot noise spectrum using the conventional gauge invariant transport theory with Coulomb interaction considered explicitly on the Hartree level along with exchange and correlation effect. Although the Fano factor is enhanced from 0.6 to 0.8 in the NDR region, the expected super-Poissonian behavior in the NDR region is not observed. When the fluctuation of Coulomb interaction is included in the shot noise, our numerical results show that the Fano factor is greater than one in the NDR region indicating a super-Poissonian behavior.   

Flux-charge duality and quantum phase fluctuations in one-dimensional superconductors

It has long been thought that superconductivity breaks down in one dimension due to enhanced quantum phase fluctuations. However, the exact mechanism for this is still an active research area. One common feature of existing theories is the idea of ``quantum phase-slip'' (QPS): quantum tunneling of the superconducting order parameter between states where the relative phase between the wire ends differs by $\pm 2\pi$. Many experiments have been carried out to investigate QPS, and a wide range of phenomena have been observed, including resistive fluctuations well below $T_C$ and an apparent quantum phase transition to an insulating state in the narrowest wires. Although these are all likely connected to QPS, a unified understanding has not yet been possible. I will describe a theory for QPS which is based on the idea that flux-charge duality, a classical symmetry of Maxwell's equations, relates the phase fluctuations associated with QPS to the well-known charge fluctuations associated with Josephson tunneling, at a microscopic level. The predictions of this theory compare favorably with a wide range of experimental observations, and may also provide a conceptual link to 2D phase fluctuation phenomena and insulating transitions in thin films.   

Intermediate state of strongly disordered superconductors

We study theoretically the superconductor-insulator transition in disordered Josephson junction arrays. Our numerical simulations suggest the existence of the intermediate state between superconducting and insulating states across the SIT that appears in a relatively narrow range of Josephson couplings. In this state the long range order parameter is absent but the excitations have a significant decay rate. We discuss the relation this finding to the experimental data that show the existence of the ``bad metal'' state characterized by a large temperature-independent resistance (J. Paramanandam, M.T. Bell, L.B. Ioffe, and M.E. Gershenson).   

Cooper pair islanding model of insulating nanohoneycomb films

Nanohoneycomb (NHC) amorphous Bi thin films, made by thermal evaporation onto substrates that contain a nanometer-scale array of holes and regular surface height variations, exhibit an insulating phase of localized Cooper pairs. Recently, we described how thickness variations induced by the substrate height variations can give rise to superconducting island formation.\footnote{Hollen et. al., Phys. Rev. B, 84(6), August 2011. This work is supported by the AAUW, the NSF through Grant No. DMR-0605797 and No. DMR-0907357, by the AFRL, and by the ONR.} Here, we will present an extension of this analysis to suggest how the island sizes evolve through the magnetic field-driven superconductor-insulator transition. Using this islanding picture, we will discuss the applicability of a granular array model to explain the appearance and behavior of the CPI phase in these films. Finally, we will discuss recent experimental tests of this proposal for thickness-undulation-driven Cooper pair localization.   

Large ferroelectric polarization in the new double perovskite NaLaMnWO$_{6}$ induced by non-polar instabilities

Based on density functional theory and group theoretical analysis, we have studied NaLaMnWO$_{6}$ compound. At low temperature, the structure has monoclinic $P2_{1}$ symmetry, with layered ordering of the Na and La ions and rocksalt ordering of Mn and W ions. By comparing the low symmetry structure with a parent phase of $P4/nmm$ symmetry, two distortion modes are found dominant. They correspond to MnO$_{6}$ and WO$_{6}$ octahedron tilt modes, often found in many simple perovskites. While in the latter these common tilting instabilities yield non-polar phases, in NaLaMnWO$_{6}$ the additional presence of the Na-La cation ordering is sufficient to make these rigid unit modes a source of the ferroelectricity. Through a trilinear coupling with the two unstable tilting modes, a polar distortion is induced, although the system has no intrinsic polar instability. The calculated electric polarization is as large as 16 ${\mu}C/cm^{2}$. Despite its secondary character, this polarization is coupled with the dominant tilting modes and its switching is bound to produce the switching of one of two tilts, enhancing in this way a possible interaction with the magnetic ordering.   

InGaZnO4 based thin film transistors with sputter-deposited PMMA/ BaSrTiO3 stacked gate dielectrics on flexible substrate

This study reports the enhanced electrical properties of InGaZnO4 TFTs with sputter-deposited PMMA/BST stacked gate dielectrics. A noticeable reduction in the leakage current density was achieved by coating a PMMA over-layer. With the introduction of sputter-deposited PMMA film with a high electrical breakdown strength and a smooth surface morphology, the leakage current characteristics were greatly enhanced. The calculated field effect mobility of the InGaZnO4 TFTs with the PMMA (30 nm)/BST (270 nm) and PMMA (50 nm)/BST (250 nm) gate dielectrics were 10.2 cm2/V$\cdot$s and 7.4 cm2/V$\cdot$s, respectively. The noticeable increase of the field effect mobility is thought to have stemmed from an interface improvement that was caused by the addition of the smooth sputter-deposited PMMA layer. The threshold voltages of the InGaZnO4 TFTs with the PMMA (30 nm)/BST (270 nm) and PMMA (50 nm)/BST (250 nm) gate dielectrics were reduced to 1.1 V and 1.6 V compared to that (1.8 V) of the TFTs with the pure BST gate dielectric. The InGaZnO4 TFTs using only sputter-deposited PMMA (300 nm) gate insulators exhibited an on/off current ratio of 4.1 $\times$ 106, field effect mobility of 36.1 cm2/V$\cdot$s at 10 V of VDS, and a relative large threshold voltage of 3.1 V.   

Transient absorption and nonlinear refractive index changes in thermally reduced nominally pure LiNbO$_3$ by sub-100-fs light pulses

Due to its polaronic features nominally undoped lithium niobate---as grown and thermally reduced---is of great interest for ultrafast optical devices. With formation times in the sub-ps-range short-lived small polarons can be generated in thermally reduced lithium niobate by optical gating of bipolarons due to single photon absorption. Simultaneously, formation of small hole polarons by two-photon-absorption is observed. In this work nonlinear absorption and refractive index changes due to exposure to sub-100-fs light pulses of 488\,nm are presented with thermally reduced crystals as an example. It is found that the two-photon absorption coefficient is not affected by the thermal reduction procedure, whereas the nonlinear refractive index change is considerably smaller in the reduced sample. We further present our results on the study of the transient absorption in the blue and NIR spectral range by means of fs-pump-probe technique. The influence of the thermal reduction procedure on lifetime and densities of electron and hole polarons is discussed.   

In-situ Characterization of Laser-Induced Crystallization in Glass Using Raman Spectroscopy

We report crystallization and other structural changes in glasses (such as LaBGeO$_5$) due to laser-induced localized heating. This heating process is a result of non-radiative decay after a photon absorption process. We explore linear absorption due to both band-to-band excitation or intentionally doped transition metal or rare earth ions using CW lasers as well as nonlinear absorption induced by high-intensity pulsed lasers. The ability to precisely position the laser on the $\mu$m length scale makes the crystallization interesting for photonic and optical applications such as waveguides and 3-D active functional devices. To better understand and control the crystallization process we are developing a combined CW laser-writing setup/confocal Raman microscope. This system will allow in-situ monitoring of the Raman emission during the crystallization. The data yielded will help elucidate the relationship between the phase, composition, and structure of the modified glass regions as a function of experimental variables, which include, but are not limited to, writing speed, irradiation time, heating rates, and defect concentration.   

Magnetoelastic coupling in doped multiferroic YCrO$_{3}$

Recent years have witnessed a renewed interest in ABO$_{3}$ structured perovskites due to possibility of combining ferroelectric and ferromagnetic order parameters in a single phase. Here we show an experimental study on one such material namely YCrO$_{3}$ which shows a phase transition from paramagnetic to a canted antiferromagnetic state at T$_{N}\sim $142K and a ferroelectric transition at T$_{C}\sim $473K. The material has an orthorhombic crystal structure ( S.G.Pbnm) In the present work, we prepared polycrystalline samples of YCr$_{1-z}$X$_{z}$O$_{3}$ (X= V or Ni) by conventional solid-state-reaction method. X-ray diffraction shows the formation of single phase material. DC magnetic measurements exhibit a magnetic transition at T$_{N}\sim $140 K and the presence of magnetic hysteresis below this temperature. Above T$_{N}$, the susceptibility follows the Curie-Weiss law with the corresponding effective magnetic moment $\mu _{eff}$ of 3.75$\mu _{B }$close to the theoretically expected value of 3.87 $\mu _{B.}$ Further, we investigated the magneto-elastic coupling in the material using temperature dependent Raman scattering. We observe 16 phonon modes below Tc. Phonon modes at 145, 403 and 422 cm$^{-1}$ showed pronounced deviation from the expected anharmonic behavior below T$_{N}$, suggesting a spin-phonon coupling below T$_{N}$ Further, we also look at the effect of doping at the Cr site on the magnetoeleastic coupling strength in this material.   

Magnetodielectric consequences in double perovskite Pr$_{2}$CoMnO$_{6}$

We report an intriguing colossal dielectric and magnetodielectric (MD) response on double perovskite Pr$_{2}$CoMnO$_{6}$(PCMO) system. At the highest applied magnetic field 9T, the giant dielectric constant around $T_{m} \quad \sim $ 175 K is enhanced almost $\sim $ 22{\%} (at 10 kHz frequency) compare with that at zero field. The observed positive MD effect is considered to be associated with the direct consequence of negative magnetoresistance changes ($\sim $ -15{\%} at 175 K). Concomitantly, a pronounced ferromagnetic ordering is observed near $T_{c} \quad \sim $ 175 K coinciding with $T_{m}$ of $\varepsilon \prime (T)$. These experimental results suggest that the magnetoresistive MD response is very much conditioned by magnetic property of PCMO.   

Enhanced ferromagnetism in co-doped BiFeO$_{3 }$ceramics

BiFeO$_{3}$ (BFO) is the most studied multiferroic material with high ferroelectric polarization as well above room temperature transition temperatures. Studies have shown significant improvements in the electrical and magnetic properties of BFO upon atomic substitutions at Bi (A) and Fe (B) sites. While enhanced ferromagnetism upon A-site doping is attributed to the suppression of cycloidal spin ordering of Fe moments, B site substitution reduces leakage current by eliminating oxygen vacancies. This study aims to combine these two aspects by co-doping the material at A- and B- sites using La$^{3+}$ and V$^{3+}$/V$^{+5}$ respectively and to investigate the electrical and magnetic characteristics of co-doped BFO. La-doped La$_{x}$Bi$_{1-x}$FeO$_{3}$ and co-doped La$_{x}$Bi$_{1-x}$V$_{y}$Fe$_{1-y}$O$_{3 }$(x = .05, 0.1, 0.15, 0.2; y = 0.03) samples were prepared solid-state reaction method. While La-doped samples show only reduced leakage without any discernible change in the magnetic characteristics, co-doped samples (La$^{3+ }${\&} V$^{5+}$ ) show significant enhancements in magnetic properties in addition to reduced leakage attributed to the elimination of oxygen vacancies. Improvement in the magnetic characteristics can be understood as a consequence of enhanced double exchange interaction between adjacent Fe ions. This argument is further strengthened by our observation that co-doped samples made by substitution of Fe with V$^{+3}$ show a magnetic response equivalent to that of only La-doped BFO samples.   

Dielectric properties and electrical conduction of high-k LaGdO$_{3}$ ceramics

The temperature and frequency dependent dielectric properties and leakage conduction mechanism in LaGdO$_{3}$ (LGO) ceramics have been studied and this material has been identified as a potential high-k candidate for the future complementary metal-oxide-semiconductor (CMOS) and dynamic random access memory (DRAM) technology nodes. The dielectric constant and the loss tangent at 100 kHz were $\sim $21.5 and $\sim $0.003 respectively at ambient conditions without any significant temperature and voltage dependence. The ac conductivity showed the typical features of universal dynamic response (UDR) and obey the double power law $\sigma _{ac} =\sigma _{dc} +A\omega ^{n_1 }+B\omega ^{n_2 }$ with three types of temperature dependent conduction processes involved; i) a dc plateau ($<$ 3 kHz) due to long range translational hopping, ii) a mid frequency region due to the short range hopping (3 -- 100 kHz), and iii) a high frequency region due to localized or reorientational hopping (100 -- 1000kHz). The temperature dependent dc conductivity followed the Arrhenius relation with activation energies of 0.05eV in the 200 -- 400 K range and 0.92 eV in the 400 -- 600 K range. The leakage current behavior revealed bulk limited Poole-Frenkel (PF) conduction mechanism with very low leakage current density (2 nA / cm$^{2}$ at 5.7 kV/cm).   

Electronic, Magnetic and Thermal Properties of Electron Doped YMnO$_{3}$

The thermal, magnetic and electronic properties of the electron doped Y$_{1-x}$Zr$_{x}$MnO$_{3}$ system were measured at both low and high temperatures. Correlations are made with structural studies on multiple length scales. Raman and IR measurements were performed at room temperature to track the changes in the phonons with doping. The effect of doping on the ferroelectric transition is examined. This work is supported by DOE Grant DE-FG02-07ER46402.   

Electrical properties of $NaSr_2Nb_5O_{15}$ ferroelectric ceramic

Since the discovery of ferroelectricity, tungsten bronze (TB) ferroelectrics has been a rapid progress in search of new TB-type materials for applications such as capacitors, actuators, transducers, ferroelectric random access memory and display technologies. The materials with TB structure have potential advantages for devices because of their high dielectric constant and low tangent loss. In view of the above importance we have studied the electrical properties of $NaSr_2Nb_5O_{15}$ (NSN) ferroelectric ceramic. The polycrystalline $NaSr_2Nb_5O_{15}$ (NSN) was prepared by mixed oxide method at high temperature. Electrical properties of NSN have been studied using complex impedance spectroscopy (CIS) with wide range of frequency ($10^2$-$10^6$~Hz) and temperature. The complex impedance plot reveals the main contribution of bulk effect. The bulk resistance has been decreased with rise in temperature. The negative temperature coefficient of resistance (NTCR) manifests a semiconductor like behavior. The ac conductivity spectrum was found to obey Jonscher's universal power law.   

Domain walls of ferroelectric BaTiO$_3$ within the Ginzburg-Landau-Devonshire model

Mechanically compatible and electrically neutral domain walls in tetragonal, orthorhombic, and rhombohedral ferroelectric phases of BaTiO$_3$ are systematically investigated in the framework of the phenomenological Ginzburg-Landau-Devonshire (GLD) model. Domain wall thicknesses, energy densities are derived analytically and evaluated numerically for several temperatures. Apart from simple Ising-type solutions of the model we also discuss more complicated solutions (two-dimensional approximation in polarization - curved polarization path). The calculations indicate that the lowest energy structure of the 109-degree domain wall and few other domain walls in the orthorhombic and rhombohedral phases resemble Bloch-like walls known from magnetism.   

Growth of CaIrO$_{3}$ and Gd$_{2}$Ir$_{2}$O$_{7}$ by MBE

Recently, it was pointed out that the 5d transition metal iridium oxides (iridates) are promising candidates to realize topological insulators, which provide a unique platform in studying the interplay of Coulomb interactions, spin-orbit coupling, and the band topology of solids. We successfully grew epitaxial perovskite CaIrO$_{3}$ and pyrochlore Gd$_{2}$Ir$_{2}$O$_{7}$ films by reactive molecular-beam epitaxy (MBE). A range of biaxial strains for epitaxial CaIrO3 films was achieved by growing on different substrates. Angle-resolved photoemission spectroscopy (ARPES) will be used to investigate the electronic structure of the epitaxial CaIrO$_{3}$ and Gd$_{2}$Ir$_{2}$O$_{7}$ films.   

Epitaxial growth of polar magnetic PbVO$_{3}$ thin films on LaAlO$_{3}$ substrates

Layered perovskite PbVO$_{3}$ (PVO) is a curious polar magnetic material, which has a potential of room temperature multiferroics. A sintered PbVO$_{x}$ ceramic target was prepared for pulsed-laser deposition. To obtain a stoichiometric single-phase PbVO$_{3}$ thin-film, it is known that control of oxygen partial pressure during the deposition is critical. With a base pressure of 10$^{-6}$ Torr, the deposition pressure was maintained as low as 10$^{-5}$ Torr, which is a severe reducing condition for most of oxide thin-films. We used LaAlO$_{3}$(001) substrates, of which lattice constant is 0.379 nm. Substrate temperature was changed from 450 to 650$^{\circ}$C. X-ray diffraction studies show that all the films show (001) oriented PbVO$_{3}$ growth but parasitic peaks are found near 39 and 42$^{\circ}$, which are presumably linked with the chervetite Pb$_{2}$V$_{2}$O$_{7}$ phase. In addition, the c-axis lattice constant of the PbVO$_{3}$ cell is decreasing and the grain size becomes bigger as the growth temperature increases. Microscopic analysis and optical measurements have been performed to investigate their local structures. However, the plume in the low pressure would generate a disperse shape of ablated ions and molecules. We will discuss how to improve the structure of the films via a new set of process parameters and their electrical properties including polarization switching and charge conduction.   

Nanoscale Periodic Modulations on Sodium Chloride Induced by Surface Charges

The sodium chloride surface is one of the most common platforms for the study of catalysts, thin film growth, and atmospheric aerosols. Here we report a nanoscale periodic modulation pattern on the surface of a cleaved NaCl single crystal, revealed by non-contact atomic force microscopy with a tuning fork sensor. The surface pattern shows two orthogonal domains, extending over the entire cleavage surface. The spatial modulations exhibit a characteristic period of 5.4 nm, commensurate with the atomic rows of the NaCl surface. The modulations are robust in vacuum, not affected by the tip-induced electric field or gentle annealing ($<$300 \r{ }C); however, they are eliminated after exposure to water and an atomically flat surface can be recovered by subsequent thermal annealing after water exposure. A strong electrostatic charging is revealed on the cleavage surface and the modulations appear to reflect a surface structural reconstruction facilitated by surface charges.   

Theoretical study of defects in \emph{c}-BC$_{2}$N

Periodic supercells with 64 atoms using a zincblende stoichiometry for \emph{c}-BC$_{2}$N are generated for various native point defects and random distribution of boron and carbon atoms in B-C-N compound. The atomic structures of these systems were relaxed by first-principles density functional theory. The elastic properties including the bulk modulus, shear modulus, and Young's modulus of the bulk \emph{c}-BC$_{2}$N crystals and the defective systems were examined and compared   

Charge trapping/de-trapping in nitrided SiO2 dielectrics and its influence on device reliability

Field effect devices with insulator gate dielectrics are excellent test vehicles to probe the physics of defects and charge trapping in the insulator/ semiconductor structure. p-channel field effect device reliability under negative bias stressing has been identified to originate from at least two terms: a) charged defect generation at the Si substrate/SiOxNy interface and b) charge trapping at neutral defect pre-cursors in the ``bulk'' of the SiOxNy beyond the interface. Measurements of transistor characteristics enable extraction of the two terms. We report the results of such measurements and demonstrate that short time effects are associated primarily with electric field assisted tunneling of holes from the inversion layer to neutral traps. This is confirmed by bias stressing measurements at different frequencies in the range 1 Hz to 2 MHz. First principles modeling of the tunneling/trapping phenomena is presented. K.Kambour worked under contract FA9453-08-C-0245 with the Air Force Research Laboratory/RVSE. Sandia National Labs is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.   

Structural, electronic, and magnetic properties of cation mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries and (Ga,Mn)N, and (In,Mn)N ternaries

ABINIT simulation package with local density approximation, generalized gradient approximation, and spin local density approximation have been used to investigate the structural, electronic, and magnetic properties of cation mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries contain equal and fixed compositions of Ga,In, and Mn atoms. In particular, total energy minimization approach have been used to compute the equilibrium structural parameters of zinc-blende (GaAs, InAs, and MnAs), wurtzite (GaN, InN, and MnN) binary parent compounds, as well as, the corresponding equilibrium parameters of the two (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternary systems. The band structures of zince-blende GaAs, InAs and MnAs binary parent compounds have been computed and analyzed. Spin polarized band structures of the cation mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries contain equal compositions of Ga, In, and Mn cations have been computed and analyzed using spin local density approximation based calculations. Moreover, the magnetic properties of (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries for equal concentration of Ga, In, and Mn cations have been investigated. Our simulations indicate that the two quaternary systems are nonmagnetic. This unusual result has been interpreted and explained. In addition, the magnetic properties of (Ga,Mn)N and (In,Mn)N diluted magnetic semiconductors will be presented.   

First Principle Ab-initio Study of TiO$_2$

We report results from first principle computations of electronic properties of rutile TiO${_2}$ within the local density functional approximation (LDA). Our first principle, non-relativistic and ground state calculations employed a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) -- utilizing a self-consistently obtained, optimized basis set. We solved self-consistently both the Kohn-Sham equation and the equation giving the ground state charge density in terms of the wave functions of the occupied states. Our calculated band structure shows that there is significant O$_2p$-Ti$_3d$ hybridization in the valence bands. These bands are well separated from the conduction bands by an indirect band gap of 2.95 eV, from $\Gamma$ to R. Consequently, this work predicts that rutile TiO$_2$ is an indirect band gap material, as all other gaps from our calculations are larger than 2.95 eV. A slightly larger, direct band gap of 3.05 eV is found at the $\Gamma$ point, in excellent agreement with experiment. Our structural optimization led to lattice parameters of 4.65 {\AA} and 2.97 {\AA} for $a_o$ and c$_o$, respectively, with a u parameter of 0.3051, and a bulk modulus of 215 GPa.   

Optically induced transient absorption related to formation of small polarons in Sn$_2$P$_2$S$_6$ in the sub-100-fs time domain

The interaction of sub-100-fs light pulses with single crystals of nominally undoped Sn$_2$P$_2$S$_6$ is studied in the NIR spectral range ($590-1630$ nm). A predominant contribution of two-photon absorption (TPA) is verified. Scans over the photon energy show that the TPA coefficient increases in a superlinear way for photon energies exceeding $E_{\mathrm g}/2$; for any photon energy it is nearly independent of propagation direction and polarization of the incident beam. The coefficient saturates at a maximum value of $\beta\approx 8$ cm\,GW$^{-1}$ at $E_{\mathrm p}\approx 1.8$ eV. It drops when reaching the bandgap $E_{\mathrm g}$. The TPA coefficients are higher by a factor of two than the values reported for other wide bandgap ferroelectrics, such as LiNbO$_3$, while being lower in comparison to semiconductor crystals. Using fs-pump-probe measurements at 626 nm, a transient absorption is observed that persists for probe pulse delays much longer than the pump pulse duration, up to 2.5 ns. Such transients are typical for a variety of wide bandgap ferroelectrics, where they are described by optically generated polaronic states. We discuss our results in the frame of the microscopic structure of Sn$_2$P$_2$S$_6$ with emphasis on the optical generation of S$^-$ small hole polarons.   

Mapping topological order in coordinate space

Topological insulators are distinguished from normal ones by the manner in which the electronic ground state is knotted in k-space. But topological order also reflects a peculiar organization of the electrons even when the concept of k-space does not make any sense, for e.g. inhomogeneous systems and finite systems within open boundary conditions. Here we only address Chern vs. normal insulators, within an independent-electron scheme in 2d. We introduce a ``topological marker'' in the form of a local Chern number, which may vary in different regions of the same sample. Since our marker samples the electron distribution locally, the boundary conditions (either periodic or open) are irrelevant. Actual simulations based on the model Haldane Hamiltonian, all of them adopting open boundary conditions, demonstrate the power of our approach. We provide perspicuous plots of our topological marker for crystalline and disordered samples, either normal or Chern insulators. We also monitor the Chern number switching in two cases: varying the Hamiltonian parameters in homogeneous samples, and addressing heterojunctions where two homogeneous regions (having different order) are joined. In all test cases our marker provides an unmistakable signature of the actual topological order.   

Vacancy-induced bound states in topological insulators

We present an exact solution of a modified Dirac equation for topological insulator in the presence of a hole or vacancy to demonstrate that vacancies may induce bound states in the band gap of topological insulators. They arise due to the $Z_2$ classification of time-reversal invariant insulators, thus are also topologically-protected like the edge states in the quantum spin Hall effect and the surface states in three-dimensional topological insulators. Coexistence of the in-gap bound states and the edge or surface states in topological insulators suggests that imperfections may affect transport properties of topological insulators via additional bound states near the system boundary.   

Electron transmittivity and reflectivity through a barrier in 2D and 3D topological insulators

We investigated theoretically the tunneling through a square potential barrier for both 2D and 3D topological insulators and their relationship to the well-known anomalous tunneling effect in graphene. Additionally, we analyzed the way in which both surface and bulk states are affected by the application of circularly-polarized light in comparison with electron dressed states in graphene where the electron-photon interaction led to the formation of an energy gap and chiral symmetry breaking of the electron eigenstates. We compare our results for topological insulators with recently obtained data for graphene. The difference arising from the presence of the bulk state energy spectrum will be analyzed and discussed in detail.   

Electronic structure of Tl2Hg3Te4 and related systems - possible topological insulators

Topological insulators (TI) have attracted considerable interest in condensed matter physics in recent years. The origin of TI behavior in 3D systems is band inversion at time reversal invariant points throughout the Brillouin zone, induced by a strong spin-orbit interaction (SOI). Motivated by this physics, we have looked at the electronic structure of Tl$_2$Hg$_3$Te$_4$ and related systems focusing on the physics of band gap formation, parentage of near-gap states, and the influence of SOI. Calculations within the GGA give a band gap of $0.48$ ($0.33$) eV in the absence (presence) of SOI, in reasonable agreement with a recent band structure calculation$^1$. However, there is no SOI-induced band inversion at the $\Gamma$ point because the lowest conduction band (LCB), which is mainly Hg s, lies below a Tl p band, suggesting that Tl2Hg3Te4 is probably not a TI. Replacing Hg by other divalent atoms may make the Tl p band the LCB, resulting in a system that may be a TI. To this end, we will discuss the electronic structures of several possible candidates. $\left[1\right]$ S. Johnsen, et. al., Chem. Mater., 2011, 23 (19), pp $4375$ to $4383$   

The Effect of Secondary Phase on Thermoelectric Properties of Zn$_{4}$Sb$_{3}$ Compound

Zn$_{4}$Sb$_{3}$ is a promising thermoelectric material because of its high thermoelectric performance and the abundance of Zn and Sb in nature. Samples of Zn$_{4}$Sb$_{3}$ with ZnSb or Zn as the minor phase were prepared to optimize the figure-of-merit (\textit{ZT}). The effects of ZnSb or Zn secondary phase on the thermoelectric properties of Zn$_{4}$Sb$_{3}$ were investigated. The highest peak \textit{ZT} of about 1.3 was achieved at 400 $^{o}$C in the sample with single Zn$_{4}$Sb$_{3}$ phase, which has the lowest thermal conductivity. Transmission electron microscopy observations of the nanostructures suggest that the precipitated ZnSb, Zn-rich nanoparticles, and nano voids, caused by volatile Zn diffusion, all contribute to the extraordinarily low thermal conductivity.   

Figure of Merit ZT achieved in Nanostructured Half Heusler alloys

Half-Heusler (HH) phases have recently gained attention due to their high temperature thermoelectric performance, especially in the environment of growing concern over the dependence on the limited fossil fuels for energy production. These materials are investigated from the perspective of thermal and electronic transport properties for enhancing the dimensionless figure of merit (ZT) at 800-1000 K. Refinement on grain sizes and embedment of nanoparticles in HH alloy hosts were employed to produce fine-grained as well as nanocomposites and monolithic nanostructured materials. Present experiments indicated that HH alloys and their nanoparticles-embedded phases can attain ZT$\sim $1, or slightly higher near 900-1000K. The observed ZT enhancements could be attributed to multiple origins. HH alloy hosts of nano-sized grains with/without embedment of different nanoparticles are also being investigated to further improve their thermoelectric performance.   

Simulation of Photon, Exciton and Charge Transports in Organic Photovoltaics based on the Dynamic Monte Carlo Method coupled with the Maxwell Equation

Organic photovoltaics(OPVs) have received increasing attention as alternatives to inorganic solar cells. To understand the physics of OPVs, the dynamic Monte Carlo(DMC) method for simulating exciton and charge carrier movements has been regarded as a suitable method. However, simulation of light absorption has been ignored. We presented a simulation of the performance of OPVs by DMC method with solving the Maxwell equation for light absorption. We especially focused on the ordered bulk heterojunction(OBHJ) OPV which is composed of P3HT and PCBM. Our analysis indicated that locations of light absorption are different at different wavelength, which suggests that the simulation of light absorption is essential. In the wavelength of 300 to 400 nm, light absorption occurred dominantly nearby the interface between the P3HT and PCBM. This implies that the generated exciton can be more efficiently dissociated into the free charges. For wavelength longer than 400 nm, most of light are absorbed away from the interface between the P3HT and PCBM. As a result of this, the internal quantum efficiencies gradually decrease from 44.6{\%} to 30.2{\%} as the wavelength increases from 300 to 700 nm.   

Fabrication of nanostructured CIGS solar cells

We present the work on Cu(In,Ga)(Se,S)$_{2}$ based nanostructured solar cells based on nanowire arrays. CIGS as the light absorber for thin-film solar cells has been widely studied recently, due to its high absorption coefficient, long-term stability, and low-cost of fabrication. Recently, solution phase processed CIGS thin film solar cells attracted great attention due to their extremely low fabrication cost. However, the performance is lower than vacuum based thin films possibly due to higher density of defects and lower carrier mobility. On the other hand, one dimensional ordered nanostructures such as nanowires and nanorods can be used to make redial junction solar cells, where the orthogonality between light absorption and charge carrier separation can lead to enhanced PV performance. Since the charge carriers only need to traverse a short distance in the radial direction before they are separated at the heterojunction interface, the radial junction scheme can be more defect tolerant than their planar junction scheme. In this work, a wide band gap nanowire or nanotube array such as TiO$_{2}$ is used as a scaffold where CIGS is conformally coated using solution phase to obtain a radial heterojunction solar cell. Their performance is compared that of the planar thin film solar cells fabricated with the same materials.   

Electronic properties and mechanism of superionic conductivity in Li$_{3}$N

Lithium nitride is a superionic conductor with high Li conductivity. The compound has been studied intensively because of its potential utility as electrolyte in solid-state batteries. Though it is known that the charge carriers responsible for conduction are Li vacancies in the Li$_{2}$N plane, the mechanism of the high mobility remains unsolved. To clarify the origin of the mobility we simulate the dynamics in the Li$_{3}$N crystal with the first principles molecular dynamics method. We have found the existence of the cooperative dynamics of Li ions in the Li$_{2}$N plane.   

Light-induced degradation in gallium-doped silicon

Light-induced degradation (LID) is a lifetime-decreasing effect in silicon solar cells attributed to the formation of B-O defect complexes during illumination [1-2]. However, Savin et al. [3] have recently observed degradation similar to LID in B- and P-doped Si contaminated with Cu, suggesting that Cu might be the cause of LID. Since Ga-doped Si is considered a degradation-free option to conventional B-doped Si [2], lifetime stability should also be studied in Cu-contaminated Ga-Si. Hence, in this paper, we intentionally contaminated high-oxygen 0.41 and 10.1 $\Omega$cm Ga-doped Cz-Si with Cu and subjected the material to illumination. No lifetime degradation was measured with $\mu$-PCD in clean Ga-Si or at low Cu levels, which is in agreement with the previously reported LID-free behavior of Ga-Si [2]. However, at higher Cu levels (20 ppb), a clear lifetime degradation was observed in Ga-Si. This lifetime degradation increased with increasing Cu concentration or with increasing wafer resistivity. [1] J. Schmidt, A.G. Aberle and R. Hezel, 26th IEEE PVSC, Anaheim, CA, USA, p.13-18 (1997). [2] S.W. Glunz, S. Rein, W. Warta, J. Knobloch and W. Wettling. Sol. Energ. Mat. Sol. C. 65, 219-229 (2001). [3] H. Savin, M. Yli-Koski and A. Haarahiltunen. Appl. Phys. Lett. 95, 152111 (2009).   

Simulation of thin nanowires for solar energy conversion: Operation as photoelectrodes and with discrete ohmic-selective contacts

Nanostructured, high aspect ratio form factors can dramatically improve the performance of solar energy conversion devices made from low cost, earth-abundant materials that are otherwise limited by poor carrier transport properties. This poster presentation identifies and more precisely defines the limiting factors in the operation of thin nanowire photoelectrodes to facilitate their design and synthesis. Results from finite-element simulations used to model the key features of thin nanowire photoelectrodes under low-level injection conditions are shown that illustrate the respective effects of nonuniform doping, tapering along the length, variation in charge carrier mobilities and lifetimes, changes in nanowire radius, and changes in the density of surface defects on the photocurrent-potential responses. Also reported are results from simulations of nanostructures featuring near-intrinsic doping densities and discrete, ohmic-selective contacts operating under high-level injection conditions. The sensitivity of device operation to contact size, carrier mobility, surface recombination velocity, doping density and illumination intensity are reported. The presented work will address the hypothesis that the discrete, ohmic-selective contact photoelectrode design affords large solar energy conversion efficiencies with thin, lightly doped semiconductor nanowires.   

Multiple Exciton Generation in Si Nanoparticles under pressure

Multiple exciton generation (MEG) in semiconductor nanoparticles (NPs) is a promising path towards surpassing the Shockley-Queisser limit in solar energy conversion efficiency. Recent theoretical and experimental studies demonstrate MEG to be more efficient in semiconductor NPs than in the bulk material [1]. However, the increased efficiency is observed only on a relative energy scale in units of the gap, as the quantum confinement effects believed to be responsible for efficient MEG in NPs also lead to a significant increase of their gap with respect to the bulk. For successful device applications, it is necessary to identify NPs with enhanced MEG rates on an absolute energy scale. We propose that Si nanoparticles with a core structure resembling that of high pressure Si phases may be promising candidates to exhibit enhanced MEG rates on an absolute scale. In the bulk, upon compression the Si gap is reduced and a recent experimental study demonstrated successful fabrication of Si NPs in the BC8 phase. In the present study we investigate the electronic structure and MEG rates of Si NPs made from the beta-tin, R8, BC8 and hexagonal diamond Si phases from first principles.\\[4pt] [1] M. Beard, J. Phys. Chem. Lett. 2, 1282 (2011)   

Crosslinkable P3HT as Hole Transport Layer of Polymer Based Solar Cells

A photocrosslinkable bromine-functionalized poly(3-hexylthiophene) (P3HT-Br) copolymer was synthesized and used as the hole transport layer in polymer solar cells based on poly(3-hexylthiophene), and low band gap polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)- 4H-cyclopenta[2,1-b;3,4-b?]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) with [6,6]-phenyl-C61-butyric acid methyl ester. Electrochemical stability of crosslinked P3HT-Br is superior to poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), which has widely been used as the hole transport material in polymer solar cells.   

First-principles calculations of covalently-bonded 3D networks of graphitic boron-nitride for hydrogen storage

Graphitic nanomaterials such as carbon nanotube (CNT) and covalently-bonded graphene (CBG) have attracted great attention due to their large surface area for high-capacity hydrogen storage. We carried out first-principles calculations based on density functional theory of covalently-bonded 3D networks of hexagonal boron nitride (hBN) layers and investigated the metal dispersion and subsequent hydrogen adsorption inside the networks. We performed a comparative analysis of stability, metal dispersion, and hydrogen sorption between graphene, CNT, hBN single layer, and 3D hBN networks.   

Simultaneous description of strong and weak H$_{2}$ adsorption sites coexisting in MOFs

In designing hydrogen-storage materials, it is a wide-spread practice to introduce transition-metal atoms into the MOF structures in order to increase the binding energy of H$_{2}$. In such systems, it is necessary to understand and describe the H$_{2}$ binding behaviors at both strong and weak binding sites. Here, we propose a model that quantitatively characterizes the hydrogen gas adsorption in the presence of different kinds of adsorption sites. Based on equilibrium thermodynamics, this model enables us to figure out the number of H$_{2}$ molecules adsorbed to each adsorbing site and the corresponding heat of adsorption. When the present model is applied to real experimental data, different binding sites are identified and the contribution of each term to the storage capacity is obtained. While the virial equation gives the isosteric heat of adsorption averaged over the system, our model gives the heat of adsorption at each adsorbed site. Furthermore, by analyzing the results of fitting, we can estimate the volume occupied by adsorbed H$_{2}$ molecules.   

Interaction of Cellulose Chains with Ionic Liquids and Water via MD simulations

One promising route for combustible fuel sources which are both renewable and have a low environmental impact is the conversion of waste biomass into tailor-made fuels. An important aspect of this process is the low-energy separation of cellulose from the biomass. Ionic liquids (ILs) have proven to be very good in dissolving cellulose with the added benefit of being essentially non-volatile making them ideal for ``green'' processing. IL research, however, remains relatively new, with many parts of this dissolution process remaining uncertain. We examine the behavior of cellulose with the ionic liquids [BMIM]Cl, [EMIM]Ac and [DMIM]DMP as well as water via MD simulation. All three ionic liquids have been observed to dissolve cellulose quite well yet have differently sized anions. We explore these differences and the impacts they have on their interactions with cellulose. First we examine the dynamics of a single cellulose strand in these ionic liquids. We determine the radius of gyration and the hydrogen bonds that are formed between the anions and cellulose. Next, we probe the dissolution mechanism of multiple, bound cellulose strands examining of multiple, bound cellulose strands examining interactions at the IL/cellulose interface and the breakup of inter-cellulose hydrogen bonds.   

Synthesis and Electrochemical Performance of SiOC-Carbon Nanotube Composite Coatings

Rechargeable battery anodes made from crystalline Si-based nanostructures have been shown to possess high experimental first cycle capacities (3000 mAh/g), but face challenges in sustaining these capacities beyond initial cycles mainly due to large volume expansion (400 percent) and chemical degradation (pulverization). Polymer-derived ceramic SiOC due to its high thermodynamic stability and nano domain structure could present a viable alternative. Additionally, functionalization of SiOC with carbon nanotubes could result in increased electronic and ionic conductivities in the ceramic. Here, we demonstrate synthesis and electrochemical characterization of SiOC-CNT composite coatings for use in Li-ion battery anode. Materials characterization performed using electron microscopy, Infrared (FT-IR), and X-ray photoelectron spectroscopy suggests non-covalent functionalization of CNT with oxygen moieties in SiOC. Sustained battery capacities of over 700 mAh/g and first cycle columbic efficiencies of about 75 percent were achieved. Future work will involve determination of lithium ion intercalation sites characterized by electron microscopy whereas cyclic voltammetry analysis will access the sequential change in anode chemistry.   

Polymer-derived Ceramic SiCN-MoS$_{2}$ Nanosheet Composite for Lithium Ion Battery Anodes

We demonstrate synthesis of a novel SiCN-MoS$_{2}$ nanosheet composite for use as Li-ion battery anode for high power applications. The nanosheet composite was prepared by thermal decomposition of polysilazane (SiCN precursor) on exfoliated MoS$_{2}$ surfaces. The morphology and chemical structure was studied using a range of spectroscopy techniques that revealed a sidewall functionalization of exfoliated MoS$_{2}$ by the polymeric precursor. The thermodynamic stability of SiCN-MoS$_{2}$ nanosheets was also confirmed by thermo-gravimetric analysis (1000 degree C). Batteries assembled using MoS$_{2}$-SiCN nanosheets as active anode material showed that lithium can be reversibly intercalated in the voltage range of 0-2.5 V with first cycle discharge capacity of 620 mAh/g at a current density of 100 mA/g.   

First principles MD simulations of proton diffusion in cubic perovskite BaZrO$_{3}$

The development of highly proton conductive and chemically stable ceramic materials, including doped barium zirconate, is particularly important for the fabrication of high performance solid oxide fuel cell (SOFCs) operating at intermediate-low temperature (550-900K). In this work, extensive first-principles molecular dynamics simulations have been employed to analyze proton self-diffusion in cubic perovskites BaZrO3. Simulations have been performed at 1300K, that are typical fuel-cells' working conditions. The runs were carried out for the stoichiometric system in unit cells of 40 atoms, and in the canonical ensemble. We also studied the effect of applied compressive and tensile stresses on the proton motion finding a non linear effect on the proton mobility as a function of the stain. Enhanced diffusion has been found for an isotropic compression of 2\% in the lattice parameter. On the other hand, the presence of a tensile strain does not seem to affect the proton diffusion, compared to the equilibrium case. The power spectrum obtained by the velocity-velocity correlation function for the proton shows no significant change in the vibrational frequencies for the strains studied.   

Effect of Surfactants on the Physical Properties and Electrochemical Performance of LiFePO$_{4}$ Cathode Material for Lithium Ion Batteries

The lithium iron phosphate chemistry is plagued by the poor electronic conductivity and slow lithium ion diffusion in the solid phase. In order to solve these problems, various research groups have adopted different strategies including decreasing the particle size, covering the particles with carbon, and adding dopants to the cathode material. Here, we report synthesis of C-LiFePO$_{4}$ cathode materials using 0.25M lauric, myristic, and oleic acid as surfactants. The phase purity of all three C-LiFePO$_{4}$~ was confirmed by x-ray diffraction. SEM and TEM investigations reveal that the surfactants coat the LiFePO$_{4}$ particles uniformly with carbon and the coating reduces the particle size to 20-30 nm. Due to high electrical conductivity, controlled particle size and suitable microstructure, among the three LiFePO$_{4}$ coated samples, the sample with 0.25M lauric acid exhibited superior electrochemical performance in terms of specific capacity, the cycling stability and delivered high discharge capacity of 155, 150 and 123 mAhg$^{-1}$ at 0.5 C, 1C and 5C, respectively. The correlation between the ratio of the intensities of the D and G bands observed by micro-Raman spectroscopy, conductivity and electrochemical characteristics will be presented.   

Block Copolymer Membranes for Biofuel Purification

Purification of biofuels such as ethanol is a matter of considerable concern as they are produced in complex multicomponent fermentation broths. Our objective is to design pervaporation membranes for concentrating ethanol from dilute aqueous mixtures. Polystyrene-$b$-polydimethylsiloxane-$b$-polystyrene block copolymers were synthesized by anionic polymerization. The polydimethylsiloxane domains provide ethanol-transporting pathways, while the polystyrene domains provide structural integrity for the membrane. The morphology of the membranes is governed by the composition of the block copolymer while the size of the domains is governed by the molecular weight of the block copolymer. Pervaporation data as a function of these two parameters will be presented.   

Toyota Prius Hybrid Plug-in Conversation and Battery Monitoring system

The objective of the project was to analyze the performance of a Toyota Hybrid. We started off with a stock Toyota Prius and taking data by driving it in city and on the highway in a mixed pre-determined route. The batteries can be charged using standard 120V AC outlets. First phase of the project was to increase the performance of the car by installing 20 Lead (Pb) batteries in a plug-in kit. To improve the performance of the kit, a centralized battery monitoring system was installed. The battery monitoring system has two components, a custom data modules and a National Instruments CompactRIO. Each Pb battery has its own data module and all the data module are connected to the CompactRIO. The CompactRIO records differential voltage, current and temperature from all the 20 batteries. The LabVIEW software is dynamic and can be reconfigured to any number of batteries and real time data from the batteries can be monitored on a LabVIEW enabled machine.   

Response of High Optical Heterogeneity in Three Dimensional Solar Cells

The incident light throughout the cavity of three dimensional photovoltaic architecture is heterogeneous, and it may influence the cell's outputs, including the open circuit voltage, short current density, and fill factor and corresponding efficiency. In this work, an equivalent circuit for three dimensional solar cells was derived by an infinitesimal method, to model the response at different light distribution. Using this model, an upper bound was given to estimate the difference between two distributions, and this can show heterogeneous light has a similar effect on open circuit voltage (Voc) as well as that from homogeneous light while low heterogeneity. We further provided a method to predict the accurate Voc on very high optical heterogeneity, such that the optimum architecture can be found to design the three dimensional solar cells.   

Soft, Hydrodynamically Coupled Particles in a Hele-Shaw Channel

Control of flowing suspensions is central to many emerging microfluidic applications. For instance, manipulation of small clusters is important in the synthesis of functional particles. Via theory and simulations, we study small clusters confined in a microchannel with thin cross section and subject to an external flow. We show that many-body hydrodynamic interactions sustain long-lived bound states with complex dynamics. As these interactions are sensitive to confinement, we investigate modulation of channel geometry as a means to perform sequential operations in a continuous process. We also probe the effects of shape and elasticity via a Lattice Boltzmann/Lattice Spring code, finding spontaneous excitation of elastic waves (``flapping''), and enriched behavior through the orientational effects of shape. Our results demonstrate phenomena that could be exploited for assembly of soft colloids in microchannels.   

Nanoparticle transport and binding dynamics in blood flow

Nanoparticulate systems have been widely used in diagnostic imaging and targeted therapeutic applications in recent years. Most current studies on nanoparticle drug delivery considered a Newtonian fluid with suspending spherical nanoparticles. However, blood is a complex biological fluid composed of deformable cells, proteins, platelets, and plasma. For blood flow in capillary, arterioles and venules, the particulate nature of the blood need to be considered in the delivery process. Non-Newtonian effects such as the cell-free-layer and nanoparticle-cell interaction will largely influence both the dispersion and binding rates, thus impact targeted delivery efficacy. A 3D multiscale particle-cell hybrid model is developed to model nanoparticle transport, dispersion, and adhesion dynamics in blood suspension. The motion and deformation of red blood cell is captured through Immersed Finite Element method. The motions and bindings of individual nanoparticles of various shapes are tracked through Brownian adhesion dynamics and molecular ligand-receptor binding kinetics. Nanoparticle dispersion and binding coefficients are derived from the developed model under various rheology conditions. The influences of vascular flow rate, geometry, nanoparticle size on nanoparticle distribution and delivery efficacy are characterized. A non-uniform nanoparticle distribution profile with higher particle concentration near the vessel wall is observed. Such distribution leads to 50{\%} higher particle binding rate compared to the case without RBC considered. The tumbling motion of RBCs in the core region of the capillary is found to enhance nanoparticle dispersion. The modeled binding results are validated through designed experiments in microfluidic devices.   

Fabrication of Out-of-Plane Electrodes for ACEO Pumps

This abstract reports the fabrication process of a novel AC Electrosmosis (ACEO) pump with out of plane asymmetric interdigitated electrodes. A self-folding technique is used to fabricate the electrodes, that depends on the strain mismatch between the tensile stressed film (metal layer) and the compressive stress film (oxidized silicon layer). The electrodes roll up with a well-defined radius of curvature in the range of 100-200 microns. Two different electrical signals are connected to alternating electrodes using an insulating silicon nitride barrier that allows circuits to cross over each other without shorting. Electroosmotic micropumps are essential for low-cost, power-efficient microfluidic lab-on-chip devices used in diverse application such as analytical probes, drug delivery systems and surgical tools. ACEO pumps have been developed to address the drawbacks of the DCEO pumps such as the faradic reaction and gas bubbles. The original ACEO microfluidic pump was created with planar arrays of asymmetric interdigitated electrodes at the bottom of the channel. This rolled-up tube design improves on the planar design by including the channel walls and ceiling in the active pumping surface area of the device.   

Design and Simulation of Optically Actuated Bistable MEMS

In this project, bistable three-dimensional MEMS actuators are designed to be optically switched between stable states for biological research applications. The structure is a strained rectangular frame created with stress-mismatched metal-oxide bilayers. The devices curl into an arc in one of two directions tangent to the substrate, and can switch orientation when regions are selectively heated. The heating is powered by infrared laser, and localized with patterned infrared-resonant gold nanoparticles on critical regions. The enhanced energy absorption on selected areas provides switching control and heightened response to narrow-band infrared light. Coventorware has been used for finite element analysis of the system. The numerical simulations indicate that it has two local minimum states with extremely rapid transition time ($<<$0.1 s) when the structure is thermally deformed. Actuation at laser power and thermal limits compatible with physiological applications will enable microfluidic pumping elements and fundamental studies of tissue response to three-dimensional mechanical stimuli, artificial-muscle based pumps and other biomedical devices triggered by tissue-permeant infrared light.   

Reactant consumption analysis in microchannel based fuel cells

In this work a miniaturized fuel cell design based on microchannels using liquid fuel and oxidizer streams is optimized for improved fuel usage. This particular design exploits the laminar nature of the fluid flow at small Reynolds numbers to keep the fuel and oxidizer confined in the vicinity of the corresponding electrodes without the need of a proton exchange membrane. Thus typical issues associated with the proton exchange membrane, such as reactant crossover, membrane dry-out and fouling are avoided. While the long term functional degradation effects associated with a physical membrane are eliminated, for an arbitrarily chosen geometry the slow thermal diffusion limits the efficiency of the cell due to the formation of depletion layers close to the electrodes. The performance of the cell is sensitive to geometry and rate of fluid flow with high aspect ratio cells operated at high Peclet number regimes being the most efficient.   

High-throughput single-cell PCR using microfluidic emulsions

The human gut and other environmental samples contain large populations of diverse bacteria that are poorly characterized and unculturable, yet have many functions relevant to human health. Our goal is to identify exactly which species carry some gene of interest, such as a carbohydrate metabolism gene. Conventional metagenomic assays sequence DNA extracted in bulk from populations of mixed cell types, and are therefore unable to associate a gene of interest with a species-identifying 16S gene, to determine that the two genes originated from the same cell. We solve this problem by microfluidically encapsulating single bacteria cells in drops, using PCR to amplify the two genes inside any drop whose encapsulated cell contains both genes, and sequencing the DNA from those drops that contain both amplification products.   

Competition in the condensation of immiscible vapors on a cold substrate

We report experimental results on the breath figures which appear upon condensation of a mixture of vapors on a cold substrate (5$^{\circ}$ C). Both fluids have similar contact angles on the chosen substrate (72$^{\circ}$ vs 90$^{\circ}$) and are immiscible. After getting the occupation diagram, we focus on the range of experimental conditions where we can see a relevant competition between the two species during the condensation. In the set of experiments, we measure the growth laws and compare them to the case of pure fluids. Also, we study the morphology of the patterns, by paying attention to the relative occupation factors and other related statistical quantities [1].\\[4pt] [1] J. Guadarrama-Cetina \& W. Gonz\'alez-Vi\~nas, in preparation.   

Adsorption kinetics of surfactants at liquid-solid and liquid-vapor interfaces from atomic-scale simulations

Nucleate pool boiling of pure liquid is a complex process involving different size- and time-scale phenomena. The appearance of the first nanobubble in the liquid at the bottom of a hot pan, the detachment of the bubble from the solid surface, its subsequent coalescence with other bubbles, all represent complex multiscale phenomena. Surfactants added to water increase the complexity of the process by contributing to the dynamic surface tension at the liquid-vapor and liquid-solid interfaces and thus affecting the heat and mass transfer at those interfaces. We apply molecular dynamics simulations to study the adsorption kinetics of anionic, cationic, and non-ionic surfactants at liquid/solid and liquid/vapor interfaces. The all-atom vs. united-atom approaches for the solid and surfactants are surveyed in view of their applicability at near boiling temperatures and a range of model water potentials is assessed for reproducing the thermal properties of water at boiling conditions.   

Experiment links the afterbounce instability and period doubled emission in single-bubble sonoluminescence

We report the first direct and long time stable observation for a single sonoluminescing bubble of the afterbounce instability that is believed to be one of the ways for a sonoluminescing bubble to lose stability and eventually break up. Furthermore we show that the instability is directly linked to the curious phenomenon of flash by flash period doubling of the sonoluminescent emission as the afterbounce instability is always period doubled whenever the emission is. This lends credit to a hot core picture coupled with refraction in the surface of the bubble. A theoretical understanding of this peculiar coupling is still missing.   

Electrohydrodynamic simulation of an electrospray in a colloid thruster

A precise understanding of electrosprays is highly interesting as the complexity of micro-technology (such as nano-material processing, spacecraft propulsion and mass-spectrometers) systems increases. A multi-component CFD-based model coupling fluid dynamics, charged species dynamics and electric field is developed. The simulations describe the charged fluid interface with emphasis on the Taylor cone formation and cone-jet transition under the effect of a electric field. The goal is to recapture this transition from a rounded liquid interface into a Taylor cone from an initial uniform distribution, without making assumptions on the behaviour, geometry or charge distribution of the system. The time evolution of the interface highlights the close interaction among space charge, coulombic forces and the surface tension, which appear as governing and competing processes in the transition. The results from the coupled formalism provide valuable insights on the physical phenomena and will be applied to a colloid thruster for small spacecrafts.   

Reaction Force of Micro-scale Liquid Droplets Constrained Between Parallel Plates through CFD

Micro-scale liquid droplets responding to depression between parallel plates are investigated analytically and numerically. The functional dependence of the reaction force accrued in such droplets on droplet size, surface tension, depression amount, and contact angle is explored. For both the 2D and 3D case, an analytical model is developed based on first principles. Computational fluid dynamics is then utilized to evaluate the validity of these models. The reaction force is highly nonlinear, initially increasing very slowly with increasing depression of the droplet, but eventually moving asymptotically to infinity. The force scales linearly with both the droplet free radius and surface tension of the liquid, but has a much more complicated dependence on the contact angle and depression. Explicit expressions for the reaction force have been determined, showing these dependencies. The 3D model has been largely supported by the CFD results. It very accurately predicts the reaction force on the upper plate as the droplet is crushed, accounting for the effect of contact angle, surface tension, and droplet size.   

Dynamics control of micro-sized droplets for fluid-based electrothermal management

Heat transfer rate across a micro-scale liquid droplet constrained in two parallel plates at various contact angles are investigated numerically. Electrowetting is used to change how fluids wet solid surfaces, and two plates are at different temperatures. Computational fluid dynamics (FLUENT) is utilized to understand the heat transfer mechanism between two plates and to evaluate the combinations of design parameters needed to produce effective electrowetting thermal management systems. When the high-thermal conductivity fluid does not wet the plates, it functions as a high thermal resistance layer, allowing limited contact surface area for heat transfer through the high-thermal conductivity fluid between the plates. However, when wettability is altered so the high-thermal conductivity fluid wets the plates, the contact area is increased substantially, leading to heat transfer action between the plates. Understanding the dynamics of fluid rearrangement as long as the heat transfer phenomena associated with the fluid rearrangement is particularly important for this system.   

A comparative study of phase separation dynamics of sulfur hexafluoride under fine and coarse temperature quenching in microgravity

Phase separation is determined by thermal quenches that break the symmetry of the homogeneous supercritical phase and leads to the formation of inhomogeneous structures with important implications for the mechanical, thermal, and electrical properties of materials. Sulfur hexafluoride (SF6) heated about 1 K above its critical temperature then quenched below the critical temperature formed gas and liquid domains in microgravity conditions. Full view and microscopic view images were analyzed to determine the changes in the size distribution of droplets. For the first time, we provided experimental evidences regarding the existence of dimple and nose coalescence mechanisms in pure supercritical fluids under microgravity conditions. We recorded data for two different thermal quenches of 3.6 mK and 0.3mK, respectively. Our results indicate that, during the late stage of phase separation, the number of the liquid clusters decreases due to the coalescence events. We estimated the power law growth of the droplets/clusters and fitted it to a universal curve.   

Microfluidic migration of soft particles in shear and Poiseuille flow

We investigate the migration of deformable particles in shear flow and Poiseuille flow due to the competition between shear forces, particle elasticity, particle diffusion, and particle inertia. At low particle Reynolds number ($Re < 1.0$), the soft particles migrate towards the channel center due to the coupling of particle elasticity and wall-induced hydrodynamic interactions. The competition between the shear forces and particle diffusivity, characterized by the Peclet number Pe, is found to affect whether the particles concentrate in the channel center of in an off-center position. As particle Reynolds number increases to moderate values ($Re \ge 1.0$), the particle concentration profile has two maxima at off-center positions. The migration effect is also found to be enhanced for softer particles with longer elastic relaxation time. The variation of particle concentration profiles leads to non-linear variations of the mixture viscosity and the average flow rate.   

Surface Design for Efficient Capturing of Rare Cells in Microfluidic Device

This work aims to design, fabricate, and characterize a micro-patterned surface that will be integrated into microfluidic devices to enhance particle and rare cell capture efficiency. Capture of ultralow concentration of circulating tumor cells in a blood sample is of vital importance for early diagnostics of cancer diseases. Despite the significant progress achieved in development of cell capture techniques, the enhancement in capture efficiency is still limited and often accompanied with drawbacks such as low throughput, low selectivity, pre-diluting requirement, and cell viability issues. The goal of this work is to design a biomimetic surface that could significantly enhance particle/cell capture efficacy through computational modeling, surface patterning, and microfluidic integration and testing. A PDMS surface with microscale ripples is functionalized with epithelial cell adhesion molecule (EpCAM) to capture prostate cancer PC3 cells. Our microfluid chip with micropatterns has shown significantly higher cell capture efficiency and selectivity compared to the chips with plane surface or classical herringbone-grooves.   

A Look at Long Term Trends and Short Term Transition Zones (Fronts) in the Atmosphere using Fourier and Wavelet Analysis

An atmospheric front can be defined as sloping zones of pronounce transition of thermal and or wind fields in the atmosphere. This study uses Fourier analysis to look at the long term trends in atmospheric data and uses Wavelet Analysis to analyze the short term transition zones. These transition zones are characterized by a strong horizontal temperature gradient and/or large horizontal wind shear. They also may have large static stability and vertical wind shear. The signature of the front is evident as a large horizontal temperature gradient and moisture gradient. The compact nature of the wavelets make them perfect candidates for analyzing the short term transition zones in the thermal and wind fields that comprise the fronts. The frequency, intensity and shape of these transition zones are analyzed.   

Sediment ripple profiles

Sand ripples are a commonly observed phenomenon in shallow-water environments with oscillatory flow. Ripple morphology reflects patterns of sediment transport and turbulence across the bottom of the bed, providing easily measurable information about the mathematical form of sediment transport laws. A set of flume experiments has been conducted to record equilibrium ripple profiles produced by a wide range of wave orbital diameters and bed shear stresses. Results indicate that normalized ripple profiles are similar across the experimental range of wave conditions: i.e., that any ripple profile can be predicted from a standard ripple shape scaled by wave orbital diameter and bed shear stress. These experiments have also quantified ripple profile asymmetry and the nonlinear relationship between ripple wavelength and amplitude.   

Optical properties of large amyloid spherulites

Amyloid Spherulites, consisting of a central core surrounded by radially oriented birefringent fibres (known as amyloid fibrils), have been found to occur in certain pathologies, such as Alzheimer's disease. Typically $\sim$5 30 m in diameter they can be observed by optical microscopy and easily distinguished by their characteristic maltese cross pattern, seen when viewed under crossed polarisers. Here we report the existence of much larger amyloid spherulites formed from bovine insulin, which grow under a particular set of conditions (10 mgml-1 BPI, pH $\sim$2.8, T $\sim$67$^{\circ}$C, 25mM NaCl) to diameters of up to $\sim$500 m. These huge spherulites when viewed under crossed polarisers in addition to the maltese cross feature beautiful coloured rings which change with the size and density of the spherulite. Such rings have been observed in other systems such as fish eye lenses and nematic liquid crystal drops and appear to be related to the rather unusual radially oriented birefringence of their internal structure. Using a ray tracing technique we model the optical path of rays through these spherulites. Taking into account refraction and the radially oriented birefringence of the amyloid fibrils, we elucidate the origin of these beautiful patterns.   

FTIR and RRS Study of the Archaerhodopsin-3 Optogenetic Neural Silencer and Transmembrane Voltage Sensor

Archaerhodopsin-3 (AR3) is a light driven proton pump from \textit{H Sodemense} with a 74{\%} sequence homology to the more extensively studied bacteriorhodopsin (BR) from \textit{H Salinarum. }Recent studies show that the wild type (WT) AR3 functions as a high-performance, genetically targetable optical silencer of neuronal activity and the mutant D95N functions as a transmembrane fluorescence voltage sensor. In order to understand the molecular similarities and differences between AR3 and BR, we compared light-activated structural changes using resonance Raman spectroscopy (RRS) and Fourier transform infrared (FTIR) difference spectroscopy$. $RRS pH titration and H/D exchange of WT AR3 showed that the retinylidene chromophore structure and Schiff base hydrogen bond strengths are almost identical to BR. RRS of the mutant D95N revealed a mixture of an N-like and O-like species at a pH greater than 7, unlike WT AR3. Low-temperature and rapid-scan time-resolved FTIR difference spectroscopy of WT AR3 revealed conformational changes during formation of the K, M and N intermediates similar but not identical to BR. Positive/negative bands in the region above 3600 cm$^{-1}$, which have been assigned to changes in weakly hydrogen bonded internal water molecules, differed substantially between AR3 and BR. These results indicate molecular differences between the AR3 and BR proton pumps which may underlie the ability of AR3 to function as a neurophotonic switch and sensor.   

Polymorphic Ab protofilaments exhibit distinct conformational dynamics as calculated by normal mode analysis

This project proposes to test the hypothesis that the physicochemical milieu modulates the conformational dynamics of synthetic Alzheimer's Ab protofilament structures, the main component of Alzheimer's senile plaques. To this end, 3D solid-state NMR structures of Ab protofilaments were used as initial structures for molecular dynamics simulations in explicit water and a water/hexane environment. The initial structures of the simulations and representative structures from the simulation-generated trajectories were taken to perform computational normal mode analysis. We developed a code in python with a graphical user-friendly interface. The program incorporated the ProDy (0.7.1) package. With the application, we examined cross-correlation plots of Ca positions of the 2-fold Ab protofilaments along the most collective mode and the slowest mode. The protofilament structures were highly correlated in the water environment. We hypothesized the protofilament would move as one in water because of the viscosity. The square fluctuation of Ca positions was calculated for the slowest mode for the hexane model and the MD generated ensemble. The two plots match up until midway through the structure. At the midway point a phase shift emerged between the two structures most likely where the surrounding changes. The in-house developed code made it easy to perform analysis and will be used by other students in the research group.   

A simple system for the identification of fluorescent dyes capable of reporting differences in secondary structure and hydrophobicity among amyloidogenic protein oligomers

Thioflavin T and Congo Red are fluorescent dyes that are commonly used to identify the presence of amyloid structures, ordered protein aggregates. Despite the ubiquity of their use, little is known about their mechanism of interaction with amyloid fibrils, or whether other dyes, whose photophysics indicate that they may be more responsive to differences in macromolecular secondary structure and hydrophobicity, would be better suited to the identification of pathologically relevant oligomeric species in amyloid diseases. In order to systematically address this question, we have designed a strategy that discretely introduces differences in secondary structure and hydrophobicity amidst otherwise identical polyamino acids. This strategy will enable us to quantify and compare the affinities of Thioflavin T, Congo Red, and other, incompletely explored, fluorescent dyes for different secondary structural elements and hydrophobic motifs. With this information, we will identify dyes that give the most robust and quantitative information about structural differences among the complex population of oligomeric species present along an aggregation pathway between soluble monomers and amyloid fibrils, and correlate the resulting structural information with differential oligomeric toxicity.   

A new multiplexing single molecule technique for measuring restriction enzyme activity

We present a new multiplexing single molecule method for observing the cleavage of DNAs by restriction enzymes. DNAs are attached to a surface at one end using a biotin-streptavidin link and to a micro bead at the other end via a digoxigenin-antidigoxigenin link. The DNAs are stretched by applying a flow. After introduction of the restriction enzyme, the exact time of cleavage of individual DNAs is recorded with video microscopy. We can image hundreds to thousands of DNAs in a single experiment. We are using our technique to search for the signature of facilitated diffusion in the measured rate dependence on ionic strength.   

Plasmon-Enhanced Single-Molecule Fluorescence for Sub-Diffraction-Limited Imaging

Super-resolution microscopy is a powerful tool for noninvasively imaging biological structures below the standard diffraction limit of light. One such technique, single-molecule fluorescence (SMF) imaging, achieves this resolution gain based on localizing isolated fluorophores. The accuracy of such localizations increases as the number of photons collected from each fluorophore increases. The ability to engineer the fluorescence quantum yield, radiative decay rate, and photostability of emitters will therefore greatly enhance the image resolution. In this work, we control SMF by coupling emission to plasmon resonances in metallic nanoparticles. These localized surface plasmons are confined charge density oscillations, and the local enhanced electromagnetic field they generate can be used to reduce the radiative lifetime and improve fluorophore brightness and photostability. We explore the effects of particle plasmons on the fluorescence properties of single dye molecules through wide-field single-molecule microscopy and fluorescence lifetime imaging microscopy experiments. All measurements are made both in the presence and absence of gold plasmonic structures. We observe up to ten-fold enhancements in photostability upon coupling to nanostructured gold, indicating that plasmon-enhanced imaging is a promising means to increase the resolution of single-molecule microscopy. We will extend our current experiments on dyes and quantum dots to fluorescent proteins.   

Fluorescence Correlation Spectroscopy of Tryptophan-containing Proteins in Sugar Solutions using Two Photon Excitation

Sugars are common ingredients for many commercial cryopreserving agents yet their function in this role is poorly understood. Some believe that sugars preferentially bind with a protein surface thereby replacing hazardous, ice-forming water. In an attempt to test idea, we have undertaken studies of the diffusion of proteins and protein-coated nanospheres using fluorescence correlation spectroscopy in an effort to determine if the hydrodynamic size is influenced by the addition of sugars. Some novelty of our approach lies in exploiting the native fluorescence of tryptophan (a common flurophore found in many proteins) by use of two-photon excitation.   

Laser Stimulated Genomic Exchange in Stem Cells. Laser Non-cloning Techniques

I propose a novel technique for a pluripotent stem cell generation. Genomic exchange is stimulated by the beat-wave free electron laser, (B-W FEL), frequency matching with the frequencies of the DNA\footnote{J.D. Watson and F. H. C. Crick, \textit{Nature}, 171, 737-738 (1953).} eigen-oscillations. B-W FEL-1\footnote{V. Stefan, B.I.Cohen, C. Joshi\textit{ Science}, \textbf{243},4890, (Jan 27,1989); Stefan, et al., Bull. APS. 32, No. 9, 1713 (1987); Stefan, APS March-2011, {\#}S1.143; APS- March-2009, {\#}K1.276.} scans entire stem cell; B-W FEL-2 probes the chromosomes. The scanning and probing lasers: 300-500nm and 100-300nm, respectively; irradiances: the order-of-10s mW/cm$^{2}$ (above the threshold value for a particular gene structure); repetition rate of few-100s Hz. A variety of genetic-matching conditions can be arranged. Genomic glitches, (the cell nucleus transfer\footnote{Scott Noggle et al. \textit{Nature}, 478, 70-75 (06 October 2011).}), can be hedged by the use of lasers.   

A one-dimensional model of Nucleosome distribution in DNA

Nucleosome positioning along DNA is neither random nor precisely regular. Genome-wide maps of nucleosome positions in various eukaryotes have revealed a common pattern around transcription start sites, involving a nucleosome-free region flanked by a periodic pattern in the average nucleosome density. We take a quantitative mathematical description of the nucleosome pattern, and incorporate specifically bound transcription factors. Our model assumes a dense, one-dimensional gas of particles, however, instead of previous work which assumes fixed-size particles interacting only by exclusion, our model explicitly accounts for transient unwrapping of short segments of nucleosomal DNA. Hence, such particles no longer have a fixed size, but interact by an effective repulsive potential. This model has been succesfully used, by us, to provide a unified description of 12 Hemiascomycota yeast species with a single unified set of model parameters. We incorporate into this model, specifically bound particles, or transcription factors (TF), which serve an important role in gene regulation. Nucleosome distribution patterns have an important influence on TF binding, and can even mediate interactions between transcription factors at a distance. This interaction can account for cooperative or competitive binding between these proteins, and we will discuss the implications this can have on gene regulation.   

Unified physical model for statistical nucleosome positioning in different yeast species

Recent genome-wide maps of nucleosome positions in different eukaryotes have revealed a common pattern around transcription start sites, involving a nucleosome-free region flanked by a pronounced periodic pattern in the average nucleosome density. For the yeast {\it S.~cerevisiae}, a gas of hard rods, known as Tonks gas and equivalent to the statistical positioning mechanism of Kornberg and Stryer, can be used to describe the experimentally observed pattern. Here, we consider 12 {\it Hemiascomycota} yeast species, each of which displays a distinct nucleosome pattern. Since the mechanisms underlying the formation of the patterns are expected to be related, we undertake a data-driven search for a unified quantitative description. We find that the simple one-dimensional gas model needs to be extended to take into account transient unwrapping of short segments of nucleosomal DNA, such that the particles no longer have a fixed size. Chromatin behavior in all but one species is well described by this generalized gas model, with a single unified set of model parameters where only the average nucleosome density is a species-dependent variable.   

Dynamics of Chromatin Silencing at Telomeres: Deterministic and Stochastic Aspects

Epigenetic silencing modifications of are often associated with well-defined domains. We study potential mechanisms of formation of boundary of silenced regions. We specially focus on the possibility that some telomeric silencing boundaries are formed in a self-organized manner, as opposed to being defined by specific boundary elements. In particular, we examine systems where a titration-induced feedback can stabilize the boundary of the silenced region. A consequence of having multiple such boundaries is large stochastic cell-to-cell variation of boundary locations. We proceed to make an argument about the nature of the fall-off of the average silencing protein occupancy, coming from such variability, and test the predictions against HA-Sir3 ChIP-seq data from experiments performed on yeast.   

Static Magnetic Field Induced Stochastic Resonance in Gene Expression

Biological systems are naturally complex, making singular responses difficult to detect. However, when the emergent behavior is investigated, the collective properties may be observed and characterized. These responses to external stimuli at are often evident at the genomic level. When an optimal dose of external noise is used to perturb the system, it may work in synergy with the system's intrinsic noise to produce a change in stable state. This phenomenon, known as stochastic resonance (SR), is responsible for shifts in gene expression. This paper proposes that static magnetic fields (SMFs) elicit a SR genomic response in biological systems under environmentally relevant exposures. Using single reporter biomarkers as well as gene expression microarrays, the responses of three cell model systems (MCF-10A; Rat-1; Caco-2) to SMF exposure were examined. Results show that while responses for a single gene do occur, they are difficult to replicate and are near the detection cutoff limits. However, the system as a whole displays a shift in the pattern of gene expression. The replication of this pattern across different experimental platforms provides evidence that the cells are responding to the noise presented by the SMFs.   

Membrane Fusion Mediated by pH-Low-Insertion-Peptide (pHLIP)

Liposomes are traditionally used as drug delivery carriers. The major mechanism of liposome entry into cell is endocytotic. First, the endocytotic pathway of cellular entry is non-specific: the delivery of therapeutics occurs to cells in both diseased and healthy tissues. Second, liposomes are usually trapped in endosome/lysosome, which prevents delivery of therapeutics to cytoplasm. We proposed to use pHLIP (pH-Low-Insertion-Peptide) to promote selective delivery of the liposome content to cytoplasm of cancer cells. We showed that liposomes coated with PEG polymer and pHLIP peptide enhance membrane fusion in acidic environments. pHLIP promotes fusion between lipid bilayer of liposome and plasma membrane or membrane of endosome/lysosome, which results in intracellular delivery of payload. Liposomes composed of 5 {\%} pHLIP and 5 {\%} PEG were ideal for the delivery. Since cancer and other pathological states produce an acid extracellular environment, this allows the liposome to target diseased tissue while avoiding healthy tissue (with neutral pH in extracellular space). The work is supported by NIH grants CA133890 to OAA, DME, YRK.   

Wide-field Time Resolved Microscopy for in-situ Lipid Phase Dynamics

We have developed a new time-resolved fluorescence platform which enables us to follow the molecular orientation and dynamics of a lipid monolayer at the air -- water interface. Confocal microscopy is limited in its ability to characterize dynamic orientation changes within cellular membranes. By implementing an all reflective Cassegrain objective we minimize dispersion while eliminating the restriction of collinear excitation. We investigate the miscibility transition of a ternary lipid mixture, DPPC / DOPC/ Cholesterol, using a combination of fluorescence imaging and spectroscopy. The technique affords unprecedented dynamic characterization for lipid orientation as the monolayer is forced from the liquid to the gel phase. We demonstrate the applicability of this device by contrasting the time-resolved fluorescence signal of three different lipid probes (NBD-PC), (BIODIPY), (Dil) which show different orientation and dynamic freedom when bound to the lipid layer for a range of lipid phases. Using this technique we can resolve highly dynamic processes such as the insertion of peptide and proteins into the lipid membrane.   

Aggregation of Phosphoinositides at Phisiological Calcium Concentrations

Phosphoinositides play a crucial role in many cellular functions such as calcium signaling, endocytosis, exocytosis and the targeting of proteins to specific membrane sites. To maintain functional specificity, it has been suggested that phosphoinositides are spatially organized in ``pools'' in the cellular plasma membrane. A possible mechanism that could induce and regulate such organization of phosphoinositides is their interaction with Ca2+ ions. Understanding the physicochemical mechanism that can regulate membrane structure is a crucial step in the development of adaptive biomimetic membrane systems. Using Langmuir monolayers, we investigated the effect of bivalent calcium and magnesium cations on the surface pressure-area/lipid isotherm of monolayers of phosphatidylinositol (PI), phosphatidylinositol bisphosphate (PIP2) and dioleoylphosphatidylglycerol (DOPG) and dipalmitoylphosphatidylcholine (DPPC). It is found that the decrease of area per lipid, i.e. the increase in aggregation, is dependent on both the lipid's head group charge, the bivalent cation and temperature. However, electrostatics are not sufficient to account for all experimental observations. Thus additional interactions between ions and phosphoinositides need to be considered.   

How evolvable are polarization machines?

In many different cell types proper polarization is essential for cell function. Polarization mechanisms however, differ between cell types and even closely related species use a variety of polarization machines. Budding yeast, for example, depends on several parallel mechanisms to establish polarity. One mechanism (i) depends on reaction and diffusion of proteins in the membrane. Another one (ii) depends on reorganization of the actin cytoskeleton. So why does yeast use several mechanisms simultaneously? Can yeast also polarize robustly in the absence of one of them? We addressed these questions by evolving budding yeast in the absence of mechanism (i) or (ii). We deleted a mechanism by deleting one or two genes that are essential for its function. After the deletion of either mechanism the growth rate of cells was highly decreased (2-5 fold) and their cell shape was highly perturbed. Subsequently, we evolved these cells for 10 days. Surprisingly, the evolved cells rapidly overcame most of their polarity defects. They grow at 0.9x wildtype growth rate and their cell shape is signifigantly less perturbed. Now we will study how these cells rescued polarization. Did they fix the deleted mechanism, strengthen other mechanisms or evolve a completely new one?   

Myosins V and VI increase actin filament flexural rigidity through a weak to strong binding transition

Myosins are ATPase molecular motors that couple ATP hydrolysis with force generation along actin filaments. Myosin alters the torsional dynamics of actin filaments, which may contribute to aspects of force generation and nucleotide-dependent stability of the actin-myosin complex. We measured how biochemical ATPase-cycle intermediate states of high-duty myosins V and VI affect the flexural rigidity of actin filaments by analyzing the angular correlation of thermally driven shape fluctuations. Both myosins increase the flexural rigidity of actin filaments in a manner that depends on the chemical state of bound adenine nucleotide. High binding affinity states increase the flexural rigidity of actin filaments more than weak binding states. These results indicate that actin filaments may flex during myosin cycling to allow bound motors to coordinate stepping.   

Time-temperature-transformation curves in chemical reactions regulated by cytoskeletal activity

Efficient and reproducible construction of signaling and sorting complexes, both on the surface and within the living cell, is contingent on local regulation of biochemical reactions by the cellular milieu with active components. We have recently proposed that in many cases this spatiotemporal regulation can be mediated by interaction with components of the dynamic cytoskeleton, where the interplay between active contractility and remodeling of the cytoskeleton results in transient focusing of passive molecules to form clusters, leading to a dramatic increase in the reaction efficiency and output levels. In this presentation, we discuss the implications of actin dynamics by introducing an ``effective temperature,'' which can work as a regulatory parameter for signaling replacing the details of actin dynamics. We show this in time-temperature-transformation plots, with the proposed ``effective temperature'' as a parameter, which paves way for discussion of active chemical thermodynamics.   

Elastic Coupling in Bipedally Crawling Cells

Periodic shape changes during cell migration are recorded in fast moving fish epithelial keratocytes where sticking and slipping at opposite sides of the cell's broad trailing edge generate bipedal locomotion and oscillatory lateral displacement of the nucleus. We use a two-dimensional finite element model to study the mechanical coupling, adhesion forces, and cell shapes that recapitulate the dynamics of these crawling cells. The model consists of elastically coupled point-like elements representing regions of the cell: leading edge, opposite sides of the trailing edge, and the nucleus. Based on simple assumptions, such as cell symmetry and localization of each element to a specific cellular region, we determine that there are only four viable permutations of elastic couplings between these four elements. We compare the four configurations and find that centralized elastic coupling to the cell nucleus and wide aspect ratio of the shape is necessary to mechanically generate realistic bipedal shape dynamics and lateral displacement of the nucleus. We suggest one configuration that is most realistic. The dynamics of this configuration are strongly dependent on the elasticity between peripheral elements, but not on the elasticity between these elements and the nucleus.   

Delivery of imaging and therapeutic agents to tumor using pHLIP

We are developing a novel technology for selective delivery of imaging probes and membrane-impermeable molecules to cancer cells. It is based on action of water-soluble membrane peptide, pHLIP$^{\mbox{{\textregistered}}}$ (pH [Low] Insertion Peptide), which has ability to insert and fold in cellular membrane at slightly acidic environment, which is a characteristic for various pathological states including cancer. The insertion of the peptide is unidirectional: C-terminus moves inside the cell across membrane, while N-terminus flags outside. Thus pHLIP possess dual delivery capability. Imaging agents (fluorescent, PET, SPECT or MRI) could be attached to the N-terminus of the peptide to mark tumor mass and tumor margins with high precision. At the same time, therapeutic molecules attached to the C-inserting end, could be moved across membrane to reach cytoplasmic target. Among translocated molecules are synthetic cyclic peptides, gene regulation agent (peptide nucleic acid) and phalla- and amanita toxins with hydrophobicity tuned by attachment of fatty acids for optimum delivery. Currently we have family of pHLIP peptides for various applications. The work is supported by NIH grants CA133890 to OAA, DME, YRK.   

The mechanics of cellular compartmentalization as a model for tumor spreading

Based on a recently developed surgical method of Michael H\"{o}ckel, which makes use of cellular confinement to compartments in the human body, we study the mechanics of the process of cell segregation. Compartmentalization is a fundamental process of cellular organization and occurs during embryonic development. A simple model system can demonstrate the process of compartmentalization: When two populations of suspended cells are mixed, this mixture will eventually segregate into two phases, whereas mixtures of the same cell type will not. In the 1960s, Malcolm S. Steinberg formulated the so-called differential adhesion hypothesis which explains the segregation in the model system and the process of compartmentalization by differences in surface tension and adhesiveness of the interacting cells. We are interested in to which extend the same physical principles affect tumor growth and spreading between compartments. For our studies, we use healthy and cancerous breast cell lines of different malignancy as well as primary cells from human cervix carcinoma. We apply a set of techniques to study their mechanical properties and interactions. The Optical Stretcher is used for whole cell rheology, while Cell-cell-adhesion forces are directly measured with a modified AFM. In combination with 3D segregation experiments in droplet cultures we try to clarify the role of surface tension in tumor spreading.   

Contour instabilities and micro-structures in early tumor growth models

Clinical diagnosis of skin cancers is based on several morphological criteria, among which growth, color, border instabilities and microstructures (e.g. dots, nests) sparsely distributed within the tumor lesion. We use the multiphase mixture models adapted to the skin to explain various patterning occurring in the avascular phase. Restricting to a simple but realistic version of these models with an elastic cell-to-cell interaction and a growth rate dependent on diffusing nutrients, we prove analytically that the tumor cell concentration at the border acts as a control parameter inducing a bifurcation with loss of circular symmetry which explains the instabilities of the tumor border. The finite wavelength at threshold has the size of the proliferating peritumoral zone. We apply our predictions to melanoma growth since these instabilities are crucial for the early diagnosis. The same model is used to show the existence of micro-structures. Taking into account a reaction-diffusion coupling between nutrient consumption and cellular proliferation, we show that two-phase models may undergo a spinodal decomposition even when considering mass exchanges between the phases. The cell-nutrient interaction defines a typical diffusive length in the problem, which is found to control the saturation of a growing separated domain, thus stabilizing the microstructural pattern. The distribution and the evolution of such emerging cluster morphologies are successfully compared to the clinical observation of microstructural patterns in tumor lesions.   

Smart-design of Tunable Nanomaterials for Enhancing Cancer Diagnosis and Radiation Therapy

Gold nanoparticles (AuNPs) will be studied for both cancer diagnosis and treatment. At present, protocols are being established using benign fibroblast cell phenotype. The diagnosis hypothesis is that approaches may be developed to examine differences in intracellular matrices of healthy and tumor cells (or to examine cell metabolic activity) via understanding the absorption and agglomeration state of intracellular AuNPs. The treatment hypothesis is that the efficacy of irradiation with laser light (and monochromatic x-rays) at killing cells after attachment of AuNPs to the external cell wall has a fundamental mechanism which may not be accounted for solely by particle heating under irradiation. It remains unclear whether quantum effects also play a role. This work will ultimately explore phonon-phonon coupling or electron-phonon coupling at the surface of the AuNP and its contribution to the observed enhanced cell death upon irradiation. Early results will be presented.   

Magnetic Hyperthermia in ferrofluid-gel composites

Magnetic hyperthermia is the generation of heat by an external magnetic field using superparamagnetic nanoparticles. However, there are still questions concerning magnetic hyperthermia in tissue; in particular the confinement of the nanoparticles at mesoscopic scales. We used Agarose and Alginate gels as models for human tissue and embedded magnetic nanoparticles in them. We report the synthesis and characterization of dextran coated iron oxide (Fe$_{3}$O$_{4})$ nanoparticles. Characterization of these nanoparticles was done using X-ray diffraction, transmission electron microscopy, magnetometry, and hyperthermia measurements. Temperature dependent susceptibility measurements reveal a sharp anomaly in the ferrofluid sample at the freezing temperature. This is conspicuously absent in the ferrofluid-gel composites. Heat generation studies on these superparamagnetic gel-composites revealed a larger heat production in the ferrofluids($\sim $4W/g) as compared to the gels($\sim $1W/g), which we attribute to a reduction in Brownian relaxation for the nanoparticles embedded in Agarose and Alginate.   

Predicting tumor sizes of ductal carcinoma in situ from immunohistochemical images using a novel approach of mathematical pathology: preliminary results, potentials and challenges ahead

Differential equation models have recently drawn increasing attentions as a useful tool to help advance the knowledge in cancer research. However, challenges remain for applying such models to clinical practices on a patient-specific basis to assist surgical decisions. Clinical diagnoses essentially at a single time point are often insufficient to fully constrain the time-dependent differential equations. Here we present a novel mathematical pathology approach, identifying robust indicators for time-invariant predictions of the model that can be used for surgical planning. We demonstrate this approach by predicting the sizes of ductal carcinoma in situ by calibrating model parameters from immunohistochemical images. Our preliminary studies of 17 excised tumor cases resulted in a better agreement with the actual measured sizes than the other estimates available to us, showing the potential of our approach for patient-specific cancer diagnosis. Conversely, our studies also revealed challenges to overcome before we can take this approach to the next level.   

Preventing biosensor non-specific adsorption: Static to dynamic interfaces

Biosensors are currently being developed for the detection of a wide range of analytes in a variety of scenarios. One such area is that of environmental monitoring for the presence of biological threats, from toxins through to viruses and bacteria. Environmental samples will contain a wide variety of contaminants, dependent on the location and prevalent environmental conditions. The sensing surfaces employed by biosensor instruments must be capable of resisting non-specific adsorption (NSA) of the contaminants whilst specifically capturing targets of interest. The ability to do so reduces the incidence of false positives and negatives increasing confidence in the system. We have assessed a range of biosensor surface chemistries of both two and three dimensional topography using a commercial BIAcore{\texttrademark} platform, for ability to prevent NSA of soluble materials of medical and military significance. This has highlighted that future solutions may benefit from dynamic interfaces as opposed to the conventional static interface often employed.   

Vertical nanowire electrode array: a highly scalable platform for intracellular interfacing to neuronal circuits

Interrogation of complex neuronal network requires new experimental tools that are sensitive enough to quantify the strengths of synaptic connections, yet scalable enough to couple to a large number of neurons simultaneously. Here, we will present a new, highly scalable intracellular electrode platform based on vertical nanowires that affords parallel interfacing to multiple mammalian neurons. Specifically, we show that our vertical nanowire electrode arrays can intracellularly record and stimulate neuronal activity in dissociated cultures of rat cortical neurons and be used to map multiple individual synaptic connections. This platform's scalability and full compatibility with silicon nanofabrication techniques provide a clear path toward simultaneous high-fidelity interfacing with hundreds of individual neurons, opening up exciting new avenues for neuronal circuit studies and prosthetics.   

1/f Noises as a Superposition of First Order Autoregressive Model

In various physical and physiological systems, power spectrum densities (PSD) of temporal sequences appear to be inversely proportion to the frequency. Those systems include the fluctuations of resistances in semiconductors, heart beats and membrane currents. Those inverse proportions of PSD to frequency are so called 1/f noises. One of the mechanisms with which 1/f noises are generated is superimposition of Ornstein-Uhlenbeck processes. Although this superimposition of Ornstein-Uhlenbeck processes, sequential temporal sequences, successfully generate 1/f noises, temporal sequences in physical and physiological systems are rarely measured sequentially. Instead, those temporal sequences are usually measured discretely. In this study, 1/f noises were attempted to generate with AR(1) processes, one example of discrete temporal sequences. As a result, PSD of superimposed AR(1) processes was inversely proportion to the frequency under some limitations. Those limitations include uniformly distribution of model parameter for AR(1) processes and white noise of driving noise. Thus, it was suggested that 1/f noises could be generated by superimposing discrete temporal sequences.   

Population dynamics on heterogeneous bacterial substrates

How species invade new territories and how these range expansions influence the population's genotypes are important questions in the field of population genetics. The majority of work addressing these questions focuses on homogeneous environments. Much less is known about the population dynamics and population genetics when the environmental conditions are heterogeneous in space. To better understand range expansions in two-dimensional heterogeneous environments, we employ a system of bacteria and bacteriophage, the viruses of bacteria. Thereby, the bacteria constitute the environment in which a population of bacteriophages expands. The spread of phage constitutes itself in lysis of bacteria and thus formation of clear regions on bacterial lawns, called plaques. We study the population dynamics and genetics of the expanding page for various patterns of environments.   

Inter- and intracellular signaling induced by magnetomechanical actuation of plasma membrane channels

Magnetic particles allow for non-invasive control over their spatial orientation and motion which makes them ideally suitable for studying real-time processes in living cells. Lithographically defined ferromagnetic disks with spin-vortex ground state have the advantage of zero net magnetization in remanence. This eliminates long-range magnetic forces which otherwise lead to the interaction between particles and their agglomeration. Moreover, magnetically soft permalloy particles have high magnetization of saturation thus requiring very low external field for inducing high magnetomotive force, compared to superparamagnetic particles. Our group has previously demonstrated that micron-sized permalloy disks can be used for destruction of cancer cells (D.-H. Kim, E. A. Rozhkova, I. V. Ulasov, S. D. Bader, T. Rajh, M. S. Lesniak, V. Novosad, Nat. Mater. 9, 165-171 (2010). In this work, we investigate the effects of magnetomechanical stimulation of human brain cancer cells with these particles. It will be shown that the actuation of ion channels in cell plasma membrane induces, on the one hand side, intracellular signaling triggering cell apoptosis and, on the other hand, it stimulates the energy transfer between the cells which carries the information about apoptotic signal.   

Bacterial sensing using phage-functionalized whispering gallery microcavities

Whispering gallery optical microcavities are structures which can efficiently confine light at the micro scale. This confinement is based on total internal reflection of light at the interface between the cavity and the surrounding medium. Devices based on optical microcavities have a wide range of applications, such as microlasers, quantum optical devices and much more. In this work, we describe a biosensing application of these optical microcavities for the label-free detection of bacteria. In order for the sensor to be specific to a particular species of bacteria, we need to properly functionalize its surface so that only that kind of bacteria will produce a signal. The microcavity surface is first functionalized using PEGylated aminosilane. We then introduce phage-derived proteins that are specific to the bacteria we want to detect. The binding between the bacteria and the phage proteins creates a perturbation to the cavity field that leads to a thermo-optic effect. This effect is then observed as a shift in the resonance features of the transmission spectrum. We performed experimental measurements using a tapered fiber to couple the light from red laser (635 nm) into the resonator.   

Flow-controlled densification in E. Coli suspension

Bacterial suspensions are paradigmatic examples of ``active matter.'' Each bacterium can be regarded as a self-propelled particle that interact hydrodynamic ally with other bacteria or the suspension boundaries. As we know, in confined environments such as micron size channels or porous systems, solid boundaries act as traps for the bacterial motion and modify drastically the macroscopic transport properties of the suspension [1]. In this presentation, we show a new phenomenon concerning E. Coli suspensions flowing through a funnel-like constrictions between two micro-fluidic channels. The applied flow induces a counter-intuitive symmetry breaking in the bacteria concentration which increases strongly past the funnel. The enhancement persists over large distances. The density dissymmetry increases linearly with the flow rate and disappears at larger flow values. The effect is reversible with the flow. We explain these observations by emerging anomalous dispersion properties due to bacterial swimming trajectories and interactions between the bacteria and the channel boundaries. This experiment opens the possibility to control the bacterial concentration in microfluidic channels by simply tuning the flow of the suspending fluid. [1] Mino et al. Phys.Rev.Lett. 106, 048102(2011).   

Small angle scattering study of the structure and organization of RNA and protein in Brome Mosaic Virus (BMV)

Brome mosaic virus (BMV) is a small icosahedral of the alpha virus-like superfamily of RNA with a segmented positive-strand RNA genome and a mean diameter $\sim $ 268{\AA} that offers high levels of RNA synthesis and virus production in plants. BMV also tightly regulates the packaging of its four RNAs (RNA1 through RNA4) into three separate particles; RNA1 and RNA2 are encapsidated separately while one copy each of RNA3 and RNA4 are normally packaged together. Small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) were applied to study the size, shape and protein-RNA organization of BMV. D$_{2}$O/H$_{2}$O mixture was used to enhance contrast in SANS measurement. The radial distribution of BMV from the Fourier transform of scattering spectrum gives a clear indication of RNA packing, and distribution and their structure in the BMV. The result reveals that the virus is about 266 {\AA} in diameter and is composed of RNA inside the virion coated with a protein shell.   

Measuring the Rate of Conjugal Plasmid Transfer and Phage Infection in a Bacterial Population Using Quantitative PCR

Horizontal gene transfer between species is an important mechanism for bacterial genome evolution. In \emph{Escherichia coli}, conjugation is the transfer from a donor(F$^{+}$) to a recipient(F$^{-}$) cell through cell-to-cell contact. We demonstrate a novel qPCR method for quantifying the transfer kinetics of the F plasmid in a population by enumerating the relative abundance of genetic loci unique to the plasmid and the chromosome. This approach allows us to query the plasmid transfer rate without the need for selective culturing with unprecedented single locus resolution. It also allows us to investigate the inhibition of conjugation in the presence of filamentous bacteriophages M13. Experimental data is then compared with numerical simulation using a mass action, resource limited model.   

Pressure-temperature dependence of growth bottlenecks and phenotypic transitions of Escherichia coli

A vast majority of bacteria and archaea can grow in diverse environmental conditions. The range of those conditions include high pressures, high temperature, low temperature, high salinity, low and high pH etc. We investigate the growth bottlenecks and phenotypic transitions of Escherichia coli (E. coli), a mesophilic bacterium, as a function of pressure and temperature. We find that E.coli can grow and proliferate in a wide range of pressures (1-400 atm) and temperatures (23-40 deg C). Moreover, we find that the division time of E. coli increases monotonically upon increasing pressure and exhibits a sharp increase in division time at pressures between 250-400 atm for all the temperatures investigated in our experiments. The sharp change in division time is followed by a sharp change in phenotypic transition of E. Coli at high pressures where bacterial cells switch to an elongating cell type. We propose that this phenotypics changes in bacteria at high pressures is an irreversible stochastic process whereas the switching probability to elongating cell type increases with increasing pressure. Furthermore, we propose an irreversible stochastic model of cell phenotype switching. We find that model fits well the experimental data. We discuss our experimental results in the light of structural and so the functional changes in proteins and structural changes in membranes at different pressure and temperature.   

Quantifying {\it E. coli} chemotaxis at the population level, with high spatial and temporal resolution

The response of microorganisms to an external chemical stimulus is key to their survival in the wild, and so has obvious connotations for natural selection. Although much is now known about the biochemical signaling pathways that allow bacteria to respond to fluctuating levels of chemoattractant in their environment, the implications for the group behavior of cells are unknown. Previous microscopic studies have focused on single-cell behavior to build up a picture of how cells adapt to changing environmental conditions. Instead of taking this approach, we borrow ideas from light scattering, and apply them to video microscopy data in a manner similar to differential dynamic microscopy (DDM). This approach places emphasis on the local density of bacteria, allowing us to study the collective behavior of around 5000 cells simultaneously with excellent spatial and temporal resolution. We use this new method in conjunction with other techniques developed in the lab to provide a comprehensive and highly automated characterization of bacterial behavior in the presence of a chemical stimulus.   

Novel Dynamics Observed in a Spiking Neural Network Model of the NTS in the Rat Hind-brain

The Nucleus of the Solitary Tract (NTS) is a hind-brain structure in the rat that is the first way-station in taste processing. Its structure and function are poorly understood. Recently our group produced a model, implemented as a spiking neural network (SNN), that successfully replicated experimental data. The model's topology was manually devised and the parameters were set by a genetic algorithm. In order to better understand its information processing capabilities, we probed the model with a variety of input spike patterns and observed a striking winner-take-all decision-making dynamic. We show how the topology and tuned parameters enable this decision to depend on precise spike timing events. It is curious that the experimental data upon which the model was originally evolved did not include winner-take-all examples; this was an emergent capability. It remains for additional experiments on rats to confirm or reject this model prediction.   

Criticality in Neuronal Networks

In recent years, experiments detecting the electrical firing patterns in slices of in vitro brain tissue have been analyzed to suggest the presence of scale invariance and possibly criticality in the brain. Much of the work done however has been limited in two ways: 1) the data collected is from local field potentials that do not represent the firing of individual neurons; 2) the analysis has been primarily limited to histograms. In our work we examine data based on the firing of individual neurons (spike data), and greatly extend the analysis by considering shape collapse and exponents. Our results strongly suggest that the brain operates near a tuned critical point of a highly distinctive universality class.   

Multidimensional representations of the phase response curve for both type 1 and type 2 membrane excitability

Neurons are complex excitable cells with a highly nonlinear response to external perturbations, such as presynaptic inputs and biological noise. Single-cell activity is determined by the properties of ionic channels and the ionic makeup of cell's environment and is mathematically described by coupled and nonlinear evolution equations. The phase resetting curve (PRC) reduces the complexity of the biophysical mechanisms involved in generating action potentials to tabulating advances or delays of subsequent spikes of a neuron due to an external perturbation. The PRC is widely used to predict the activity of large neural networks that by replacing the computationally intensive integration of evolution equations with lookup tables. The fundamental assumption of the PRC approach in predicting phase-locked modes in coupled neural networks is that the transient PRC measured for isolated and bursting neurons (open-loop) remains the same under the recurrent inputs of a phase-locked mode (close-loop). The novelties of our approach are: 1) the use of discrete sine transforms (DST's) to store the PRC's as a series of coefficients, and 2) the use of multidimensional stacks to represent multidimensional objects.   

Hamiltonian Dynamics of a Forced Two-Degree-of-Freedom Arm with Viscoelastic Muscles Executing Planned Motions

In order to improve our understanding of how the brain controls the human arm both in the presence and absence of gravity, we have developed a two-degree-of-freedom robotic arm which is driven by six servo-actuated viscoelastic muscles. The computer-controlled servos mimic the contractive action of the sarcomeres in actual muscles, sections of elastic tubing represent the elastic behavior of actual muscles, while the behavior of tendons is represented by inelastic strings.~The servos receive instructions to move from the visual C++ platform in the computer and the actual motion of the arm is recorded with optical encoders built into each joint axis. This experiment is a purely feed-forward system, and our goal is to determine whether our equations of motion, formulated using Hamiltonian dynamics, when numerically integrated, will predict the observed motion of the arm within experimental uncertainties. Our research was selected as one of 12 teams chosen nationwide as part of NASA Grant Us Space Reduced Gravity Program, to fly and perform experiments aboard NASA's Weightless Wonder aircraft in Summer 2011.   

Modeling the Force Frequency Relation of a Cardiac Cell

Recent pacing experiments with hearts of rat have discovered that the contractile response of the hearts can have an unexpected slow non-monotonic response. This later observation cannot be explained by the existing excitation-contraction coupling model. A new discrete map model of the EC coupling is developed to understand these experimental findings. It is found that the biphasic response and the slow time scale can be reproduced when a calcium feedback based on calcium regulation mechanism of the cell is introduced. Furthermore, this model can also reproduce the nonlinear dynamical properties of the system; such as the period doubling in the response of the contractile forces during a step change in the pacing period. The force frequency relation curve generated by the model also compare well with previous published data. Our findings suggest that the feedback is really needed to understand the calcium transient when pacing frequency is changed and the calcium regulation is very important for the calcium handling of cardiac myocytes.   

Simulating Growth Dynamics of Neurons on Substrates

We present computer simulations of neuron growth in which growth cones both create and are guided by growth promoter molecules which move diffusively. Our model predicts several features of the trajectories that are experimentally measurable, including arclength and curvature as functions of time. By comparing these predictions to time-lapse microscopy experiments of axon growth in a controlled environment, we gain new insights into neuronal growth and connectivity.   

Controlling growth and electrical connectivity of neuronal cells patterned on surfaces

In the developing brain biochemical and geometrical cues are an essential source of information used by neurons when wiring up the nervous system. However, our current understanding of the mechanisms by which various guidance factors control the path that growing axons/dendrites follow to reach their targets and form functional electrical connections remains qualitative. A current limitation for the study of neural network formation is the ability to precisely control the growth and interconnectivity of small numbers of neurons. Here we present a combined Atomic Force Microscopy - Fluorescence Spectroscopy approach for patterning neurons on 2-dimensional substrates and precisely controlling their location, growth and interconnectivity. We demonstrate that this approach allows one to: a) form simple neuronal circuits in well-controlled geometries; b) guide the formation of functional synapses between neurons, and c) measure the electrical activity of small groups of neurons. We also discuss the implications of these results for our current understanding of the fundamental mechanisms that govern the development of electrical connections between neurons.   

Are the laws of nature Markovian?

The present laws of physics are Markovian. The state of the world at the current time step, t, depends only on the state of the world at the previous time step, t-1. (If there happen to exist closed timelike curves in our world then general relativity suggests that this may not be true even in physics.) But other sciences may propose laws which are nonMarkovian. Biology (evolution) has the memories stored in DNA, cognitive science has long term and short term memories, economics may exhibit behavior (cooperation) that depends on a memory of past events, etc.   

Optical properties of thylakoid stacks

Optical properties of grana are simulated by means of 4x4 matrix approach (Berreman method). The results of calculations lead to a conclusion that even small degree of chirality, that may be present in a granum structure, results in the dramatic changes of its optical properties. Depending on the birefringence and degree of chirality in granum organization the reflection of left or right handed circularly polarized light can be greatly suppressed. This can explain the light induced difference in the growth of pea and lentil shoots irradiated by left and right handed circularly polarized light [1]. \\[4pt] [1] Pavel P. Shibayev, R.G. Pergolizzi, The effect of circularly polarized light on the growth of plants, International journal of botany, 7, 113 (2011)   

The Use of Magnetite as a Polarisable Anode in the Electrolysis of Water

We have studied the oxidation of magnetite to $\mathrm{Fe}_2\mathrm{O}_3$ in an electrolytic cell in which the cathode is magnetite and the anode is platinum. We report cyclic voltammogram data consistent with the hypothesis that magnetite, without oxygen gas production but with hydrogen gas production at the anode, is occurring. The reaction occurs at a potential at the cathode of about 0.3V vs SCE in 1M NaOH electrolyte, consistent with colloid experiments which also estimated the equilibrium potential of the hypothesized reaction. We find currents on the order of a milliamp per gram of magnetite electrode with the pelletized magnetite powder electrodes which we are using. Electrode characterization results using BET, XDS and macroscopic volume and mass measurements are reported, as well measurements of the amount of hydrogen gas generated per unit current. The quantity of gas generated is also consistent with our hypothesis concerning the electrode chemistry. Some samples exhibit evidence of two oxidation reactions occurring at the cathode and a possible interpretation of these is also discussed.   

Interficial Electron Transfer from a PbSe Quqantum Dot into the TiO$_{2}$ Surface

We reporte an \textit{ab initio} nonadibatic molecular dynamics (NAMD) simulation of ultrafast photoinduced electron transfer (ET) from a PbSe quantum dot (QD) into the rutile TiO$_{2}$(110) surface. The simulation supports the obervation that the ET successfully competes with energy losses due to electron-phonon relaxation. The ET proceeds by the adibatic mechanism due to strong donor-acceptor coupling. High frequency polar vibrations of both QD and TiO$_{2}$ promotes the ET, since these modes can rapidly influence the donor-acceptor state energies and coupling. Low frequency vibrations generate a distribution of initial conditions for ET, which shows a broad variety of scenarios at the single-molecule level. The system exhibits diverse scenarios for individual electron injection events, involving a complex interplay of ET mechanims, time scales, and phonon dynamics.   

Semiconducting (Half-Metallic) Ferromagnetism in Mn(Fe) Substituted Pt and Pd Nitrides

Using first principles calculations as based on density functional theory, we propose a class of so far unexplored diluted ferromagnetic semiconductors and half-metals. Here, we study the electronic properties of recently synthesized {\it 4d} and {\it 5d} transition metal dinitrides. In particular, we address Mn- and Fe-substitution in PtN$_2$ and PdN$_2$. Structural relaxation shows that the resulting ordered compounds, Pt$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$ and Pd$_{0.75}$(Mn,Fe)$_{0.25}$N$_2$, maintain the cubic crystal symmetry of the parent compounds. On substitution, all compounds exhibit long-range ferromagnetic order. While both Pt$_{0.75}$Mn$_{0.25}$N$_2$ and Pd$_{0.75}$Mn$_{0.25}$N$_2$ are semiconducting, Fe-substitution causes half-metallic behavior for both parent materials.   

Time-dependent Partition Density-functional Theory

We present an extension of time-dependent density functional theory that allows to partition the time-dependent external potential in terms of localized molecular fragment potentials. As a consequence, localized time-dependent densities arise for each molecular fragment. To enforce the condition that the sum of fragments must add up to the exact total density, a new quantity termed ``time-dependent partition potential'' is introduced. The Runge-Gross theorem is employed to show that there is a quasi one-to-one correspondence between the partition potential and the electronic density. The corresponding quantum-mechanical actions are derived by using the van Leeuwen's action and are used to derive a decomposition of the partition potential which allows for practical approximations. Linear response formulas are deduced to obtain the transition energies, and an approximation is suggested to obtain localized excitations in large molecular systems. Finally, numerical illustration of our theory is shown for one-dimensional fermions under the influence of a laser field.   

A Density Functional Approach to High Harmonic Generation

The role of the asymptotic behavior of the ground state exchange-correlation (xc) potential is examined for the case of high harmonic generation (HHG) in N$_2$ via Time-dependent Density Functional Theory (TDDFT) within the adiabatic approximation. High harmonic generation (HHG) is a high-energy phenomenon that has been theoretically investigated using the strong- field approximation (SFA) within the single active electron approximation (SAEA) for small molecules. In the case of N2, experimental results for characteristic features of the harmonic emission suggest a breakdown of those approximations. TDDFT bypasses the need for such approximations as it accounts for all the electrons in the system; however, it requires approximations to the xc-potential. We investigate how asymptotic corrections to the Local Density Approximation (LDA) xc-potential influence the HHG spectrum.   

Measuring the Performance of Generalized Gradient Approximations in Solids

There recently have been a number of generalized gradient approximations (GGA's) developed to address a major limitation of the approach--the inability to model both energies and structural constants at the same time. We examine the performance for bulk systems of four different GGA exchange-correlation (XC) functionals: the PBE functional, best for energy calculations in molecules, the PBEsol functional developed to improve calculations of solid structures, the SOGGA functional developed to improve lattice constant calculations, and the VMT1 functional developed to improve atomization energy calculations without a loss in lattice constant accuracy. These XC functionals are tested on a set of 12 solids composed of metals, semiconductors, ionic metals, and transition metals. The plane-wave DFT code ABINIT was used to calculate the cohesive energy for each solid using each XC approximation. The bulk moduli and lattice constants were determined by fitting to the Murnaghan equation of state. We look particularly into how the use of a pseudopotentail will effect the predictions of each model in comparison to experiment.   

Investigating optical properties of Atmospheric gases using multi-color collocated Laser system: an application of elastic and inelastic backscattering

The application of nanosecond pulsed lasers to probe optical properties of atmospheric gases by the application of elastic and inelastic backscattering mechanisms, is one of the most effective tools to investigate atmospheric gases effect on short and long term climate changes. Capabilities, properties, and limitations of newly built multi-color lidar (light detection and ranging) system at the CARE facility, Ontario, Canada, will be presented and thoroughly discussed. CARE's setup utilizes elastic and inelastic backscattered signals of the second (532 nm), third (355 nm), and forth (266 nm) harmonic outputs of simultaneously employed YAG lasers, which are manipulated to investigate optical properties of ozone, water vapor, and nitrogen molecules up to 25 km geometrical altitude. In particular, by employing inelastic backscattering lidar signals of Raman nitrogen channel (386.7 nm) and Raman water vapor channel (407.5 nm), vertical profiles of water vapor mixing ratio (WVMR) from the near ground up to 12 km geometrical altitude are deduced, calibrated, and compared against WVMR profiles obtained from collocated radiosonde launches. Furthermore, a detailed theoretical treatment to the lidar technique will be presented and related to recent experimental findings.   

Nonspherical structure of aqueous organic nanodroplets

The structure of nanodroplets plays a critical role in many natural phenomena involving atmospheric nucleation and aerosol formation. Here, we review our experimental and theoretical work on the structure of nonane/water nanodroplets. The experiments involve small angle x-ray scattering (SAXS) of nanodroplets formed in supersonic nozzles. Classical density functional theory (DFT) calculations of species density profiles are made in cylindrical coordinates, which allows for the possibilty of non-spherical droplets under appropriate conditions. One key theoretical result is the occurrence of a nonspherical Russian-Doll (RD) structure at low temperatures that is confirmed by molecular dynamics (MD) simulations. Some, but not all, of the measured SAXS spectra can be well-fit by a simple RD model, but the poor x-ray contrast between nonane and deuterated water generally makes it difficult to distinguish among well-mixed, core-shell, and RD structural models.   

Investigation of Forces Exerted During the Expansion of Nanomechanically Tensioned Organosilica Materials

Osorb\textregistered is a sol-gel derived organosilica that instantaneously swells up to four times in volume with organic liquids. The nanoporous glass-like material is hydrophobic and does not swell in water but absorbs non-polar organic solutes from aqueous solution. Swelling due to absorption of organic solutes, liquids, or gases leads to the generation of substantial mechanical force, presumably derived from the relaxation of the interconnected network of organosilica nanoparticles that comprise the material. We have investigated the force exerted by placing a powdered sample in a cylinder with a freely movable piston. As solvent percolates into the cylinder from below, the exerted force is measured by a load cell. The piston is then gradually moved upward to allow the material to expand. As the sample just begins to swell, we have routinely observed forces in excess of 500 N per gram; the exerted force then decreases as the volume is allowed to increase. The relationship between the exerted force and sample volume is shown to be exponential, and we define the exponential decay constant as the characteristic volume $V_c$. We also determine the absorption capacity and fractional change in volume of the organosilica samples, and correlate these with changes in $V_c$.   

2D IR Spectroscopy of Nucleic Acid Bases and the Folding of DNA Aptamers

DNA can adopt a wide variety of conformations that have important roles in their biological functions, such as DNA packaging, replication, and protein recognition. Vibrational spectroscopy is known to reflect DNA conformation, and basic assignments of resonances in the IR and Raman spectra of nucleic acids have existed for decades. However, traditional spectral assignments are based on simple local vibrational mode basis such as C=O and C=N double bond stretches, although computational studies describe highly delocalized vibrations. We acquired polarization dependent 2D IR spectra of the base vibrations of five nucleotide monophosphates (NMPs) as the building blocks for developing a model of DNA and RNA vibrational spectroscopy. The distinctive cross-peaks between the vibrational modes of NMPs, such as ring vibrations and C=O stretches, indicate that these vibrational modes are strongly coupled anharmonic oscillators. We have characterized the eigenstate energies, vibrational anharmonicities, transition dipole strengths, and their relative orientations through the analysis and modeling of the experimental 2D IR spectra. We are currently applying this knowledge to study the folding of some G-rich DNA aptamers.   

Intense-field ionization of heterocyclic organic molecules: fragmentation and metastable states

Pyridine and the diazine molecules (pyridazine, pyrimidine, and pyrazine) are ionized by intense-field, ultrafast (50 fs), 800 nm laser pulses, and the resulting ion mass spectra are recorded as a function of laser intensity (ranging from $\sim $10$^{13}$ W/cm$^{2}$ to $\sim $10$^{15}$ W/cm$^{2})$. Log-log plots of ion yield vs. intensity suggest resonance-enhanced multiphoton ionization (REMPI) mechanisms. These measurements are made possible by a unique tuning of the time of flight mass spectrometer that eliminates the focal volume effect in the ion yields. We also report on the fragmentation of the molecular ions under these same conditions. Fragment ion yields vary greatly when measured from different molecular parents, even those coming from the same mass. Furthermore, we observe evidence of metastable decays in the ion mass spectrometer, and measure the decay product mass by deliberately detuning the potentials on the time of flight mass spectrometer. This result is presented as a method of determining the nature of the metastable fragments---their masses and kinetic energy distributions.   

Photoionization cross sections of atomic impurities in spherical quantum dots

Quantum dots with atomic impurities have attracted considerable attention due to not only its theoretical but also practical significance. The confinement potentials associated with the structure of quantum dots are often described by the rectangular potential well or harmonic oscillator potential. However, the non-parabolic shape at the center for the rectangular well and the infinite depth for the harmonic oscillator potential make the models unrealistic in practical applications. Recently, the finite oscillator and Gaussian potentials are proposed to mimic the spherical quantum dots, which are defined respectively as $V_{FO} (r)=-A(1+{Br} \mathord{\left/ {\vphantom {{Br} {\sqrt A }}} \right. \kern-\nulldelimiterspace} {\sqrt A })\exp (-{Br} \mathord{\left/ {\vphantom {{Br} {\sqrt A }}} \right. \kern-\nulldelimiterspace} {\sqrt A })$ and $V_G (r)=-C\exp ({-r^2} \mathord{\left/ {\vphantom {{-r^2} {D^2}}} \right. \kern-\nulldelimiterspace} {D^2})$ with the confining strengths A and C, and the radii of quantum dots 1/B and D. In this work, the method of complex-coordinate rotation in the finite-element discrete variable representation is implemented to study the photoionization of atomic impurities in spherical quantum dots. We explore the energy spectra and photoionization of atomic impurities influenced by the quantum confinement. The shifting of Cooper minima caused by the quantum confinement is observed.   

A DFT Study of Palladium Clusters and their Reactions with H$_{2}$ and O$_{2}$: Application to catalyzed H$_{2}$O$_{2}$ synthesis

Adsorption of oxygen and hydrogen in both atomic and molecular forms on small Pd$_{n}$,~clusters (n=2-13 and 19) is investigated using density functional theory. An extensive search for the energetically preferred structural forms and spin states of the clusters is performed. The geometries and energetics of the cluster-adsorbate systems and their transition states are mapped out as well. Cases of both single and multiple adsorptions are considered, and trends in the saturation coverage of the clusters versus cluster size are examined. Edge sites are found to be energetically preferred for O$_{2}$ adsorption, whereas the atop sites favor binding of H$_{2}$. Atomic adsorption of hydrogen is examined as well and limits to the number of H atoms that can be dissociated on each size cluster are found. In order to understand how trends in the results extend to larger cluster sizes, limited calculations have also been performed for Pd$_{55}$. The role of Pd$_{n}$ clusters as catalysts for production of H$_{2}$O$_{2}$ from H$_{2}$ and O$_{2}$ is discussed as well.   

Morphologies of an anisotropic diffusion limited growth model to study electroless deposition

We report results of Monte Carlo simulation of a model which mimics certain aspects of electroless deposition of metals on polymeric surfaces. In the proposed model growth germinates from certain ``active'' particles residing on a flat surface. Further growth occurs via sticking of a diffusing particle while it is within the range of one of these active particles. Once within the attractive range of an ``active'' particle, the motion of the approaching particle is considered ballistic. This newly adsorbed particle then acts as an ``active'' site for further growth and the process continues. We monitor the layer by layer density variation, the pair correlation function and the structure factor as a function of the initial density of the particles and the range of the reaction, and comment on the fractal aspect of the morphology.   

Magneto-optical contrast in liquid-state optically-detected NMR spectroscopy

We use optical Faraday rotation (OFR) to probe nuclear spins in real time at high-magnetic field in a range of diamagnetic sample fluids [1]. This technique is shown to speciate functional groups with the same chemical shifts as is seen in conventional NMR, however, the intensities of the OFR-NMR peaks are influenced by optical detuning and hyperfine couplings. We investigate protons at chemically-distinct sites and other lower-gyromagnetic-ratio nuclei including carbon, fluorine and phosphorous [2]. Binary mixtures for protonated systems were also tested and the results suggest that the present approach is sensitive to the solvent-solute dynamics in ways complementary to those known in inductive NMR. \\[4pt] [1] D. Pagliero, W. Dong, D. Sakellariou and C. A. Meriles\textit{. J. Chem. Phys.} 133, 154505 (2010). \\[0pt] [2] D. Pagliero and C. A. Meriles. \textit{Proc. Natl. Aca. Sci.} USA (2011) in press.   

Hypo/hyperchromy in orthorhombic molecular crystals: Fluorene, and Dibenzofuran

The transmission of Fluorene and Dibenzofuran molecular crystals was measured over the near ultraviolet to vacuum ultraviolet (4-10 eV) range at the National Synchrotron Light Source. Polarized spectra were measured for both $a$ and $b$ crystallographic axes, and the spectrum in the $c$ direction was found using the spectrum of a $40^\circ$ rotated sample. Oscillator strengths were calculated by fitting the data to the Drude-Lorentz model. Comparison of the oscillator strength in the gas phase and in crystal show significant differences. These differences are attributed to the effect of intermolecular interaction in these molecular crystals.   

Superradiant light source for atmospheric remote sensing

We have studied coherent emission from ambient air and demonstrated efficient generation of laser-like beams directed both forward and backward with respect to a nanosecond ultraviolet pumping laser beam. The generated optical gain is a result of two-photon photolysis of atmospheric O2, followed by two-photon excitation of atomic oxygen. We have analyzed the temporal shapes of the emitted pulses and have thereby shown that a large atomic coherence may well be responsible for the observed temporal structures. Our results suggest that the emission process is coherence brightened in its nature, and is to be compared with ordinary lasing where atomic coherence remains small on the one hand and cooperative Dicke superradiance where atomic coherence is maximized on the other. The collective coherence in this process adds insight as to the optical emission physics. The present superradiant source holds promise for remote sensing techniques employing nonlinear spectroscopy.   

Estimating the contributions to the Low Energy Tail in Cu and Ag (100) using Positron Annihilation Auger Electron Spectroscopy

Low energy Auger lineshapes are difficult to measure because they sit on a large background due to secondary electrons arising from loss processes unrelated to the Auger mechanism. In this poster we discuss the implications of our Positron Annihilation Auger electron Spectroscopy (PAES) measurements of the ratio of the integrated Auger Peak and integrated low energy tail (LET) intensities for comparisons between theoretical and measured values of the Auger intensities. The experiments were carried out at university of Texas at Arlington on Ag (100) crystal. The various contributions to the low energy tail are highlighted in terms of processes intrinsic and extrinsic to the Auger mechanism. Our conclusions regarding the importance of the LET in determining the ratio of electrons in the Auger peak to the number of initial core holes are discussed in light of the electron stimulated Auger results obtained by Seah et al. using monte carlo simulations on various elements.   

Peroxynitrous Acid Dimer: Ab Initio Density Functional Study

Peroxynitrous acid (PNA) HOONO, isomeric to nitric acid, is a very strong oxidant. A novel \emph {dimeric} hydrogen-bonded cluster of peroxynitrous acid (PNA-D) is proposed herein; \emph {ab inito} quantum chemical investigations performed whereupon lead to several stable structures that have a direct bearing on the reactivity of the participating monomers, quantified in terms of the molecular electrostatic potential. The electron-correlation lending stability to PNA and its dimers is gauged through several density functionals namely B3LYP, B3PW91, M06-2X, M06-L, and $\omega$-B97X, etc.; as well as from popular wave-function based second order M\o ller-Plesset (MP2) perturbation theory, using the basis sets 6-311++G(d,p) and 6-311++G(2d,2p). The infra-red vibrational spectra reveal spectral shifts and intensity redistribution after dimerization. While the lowest energy PNA-D has a perfect inversion symmetry; the other stable dimers emerge as combinations of monomers in different orientation.   

High resolution infrared spectra of protonated benzene isolated in solid parahydrogen

Identification of infrared (IR) spectra of protonated polyaromatic hydrocarbons (PAH) is important in understanding the unidentified IR bands of interstellar media. We demonstrate a new method that is superior to the Ar-tagging IR photodissociation or the IR-multiphoton-dissociation (IRMPD) methods currently used. The protonated benzene (C$_{6}$H$_{7}^{+})$ was produced on electron bombardment of a mixture of benzene (C$_{6}$H$_{6})$ and \textit{para}-hydrogen ($p$-H$_{2})$ during deposition. IR features of C$_{6}$H$_{7}^{+}$ and C$_{6}$H$_{7}$ were identified by observing the change in intensity upon photolysis and comparison with theoretical calculations. Lines of C$_{6}$H$_{7}^{+}$ decreased in intensity when the matrix was irradiated with light at 365 nm, those of C$_{6}$H$_{7}$ increased in intensity. Similar experiments were performed for a sample of C$_{6}$D$_{6}$/$p$-H$_{2}$ and the production of C$_{6}$D$_{6}$H$^{+}$ was confirmed. Observed wavenumbers, relative IR intensities and deuterium isotopic shifts agree with those predicted for C$_{6}$H$_{7}^{+}$ and C$_{6}$H$_{7}$. Compared with previous methods, this method provides a wider spectral coverage with much narrower lines and more accurate relative IR intensities, and may be readily applied to larger protonated and neutral PAH.   

Pressure-temperature surface phase diagrams of LaMnO$_3$ surfaces in oxidative environments from first principles based kinetic Monte Carlo simulations

Perovskite oxide surfaces catalyze many important oxidation reactions. They are also promising for oxygen ion conducting cathode materials in solid oxide fuel cells and efficient catalytic components for removal of NO$_x$ gases in auto exhausts. Oxygen interaction with perovskite surfaces is of central importance in all such above mentioned technologically relevant examples. Here, we have employed first-principles based kinetic Monte Carlo (kMC) simulations to investigate the relative stability of the clean as well as molecular and atomic oxygen covered LaMnO$_3$ surfaces over a vast range of temperatures and oxygen partial pressures. The energetics as well as the activation energies of various surface reactions (adsorption, desorption, surface dissociation, and the surface diffusion of molecular and atomic oxygen) were computed and used in large-scale kMC simulations to predict the surface oxygen content and configuration at various combinations of temperature and pressure, thereby yielding a surface phase diagram. Owing to the state-of-the-art theory, algorithms and computations employed, these results are believed to represent the real situation with high fidelity. The phase boundaries as predicted by our kMC simulations are identified to be the catalytically active regions.   

A New Technique for the Direct Determination of the Quasi-free Electron Energy in Dense Fluids

Previous experimental studies of the quasi-free electron energy $V_0(\rho)$ in fluids of density $\rho$ either directly measured $V_0(\rho)$, using photoemission from an electrode immersed in the fluid, or extracted $V_0(\rho)$ from field ionization of a dopant dissolved in the fluid. We present a new method to determine $V_0(\rho)$ directly, namely field enhanced photoemission. We show that this new method yields data of comparable quality to those obtained from dopant field ionization, thereby greatly improving on prior direct photoemission studies. Moreover, unlike dopant field ionization, field enhanced photoemission is not limited by the solubility of a dopant in the fluid of interest.\\[4pt] The experimental measurements reported here were performed at the University of Wisconsin Synchrotron Radiation Center (NSF DMR-0537588). This work was supported by grants from the Petroleum Research Fund (45728-B6) and from the National Science Foundation (NSF CHE-0956719).   

Nonequilibrium Phase Transitions in Supercooled Water

We present results of a simulation study of water driven out of equilibrium. Using transition path sampling, we can probe stationary path distributions parameterize by order parameters that are extensive in space and time. We find that by coupling external fields to these parameters, we can drive water through a first order dynamical phase transition into amorphous ice. By varying the initial equilibrium distributions we can probe pathways for the creation of amorphous ices of low and high densities.   

Investigating the Glass Transition Temperature of Water using a Variety of Models and Methods via Molecular Dynamics Simulation

In everyday life, we think of solid water existing as crystalline ice. The majority of water in the universe, however, exists as an amorphous solid or ``glassy'' form. This glassy form has garnered significant interest and sparked sizable debate in recent years over the nature and conditions surrounding the transition from liquid to amorphous solid, not the least of which centers on the determination of the glass transition temperature. Previous experimental studies have suggested a glass transition temperature below the temperature at which water undergoes homogeneous nucleation, thus making experimental determination of the glass transition temperature difficult because of the need to avoid ice formation. In this study, we have used molecular dynamics simulation to study the structure, order and dynamics of water molecules at small timescales and under rapid cooling conditions to elucidate the formation of the amorphous solid and better understand the glass transition. Constant-pressure and constant-volume simulations have been performed in order to examine convergence or divergence of water dynamics under differing conditions. In addition, the van der Waals energy of simulation systems has been examined in an attempt to identify the glass transition temperature in a way that, to our knowledge, has not previously been used. Results suggest a glass transition temperature higher than previous widely accepted values but comparable to more recent results.   

Ion size effects on the electrokinetics of spherical particles in salt-free concentrated suspensions

In this work we study the influence of the counterion size on the electrophoretic mobility and on the dynamic mobility of a suspended spherical particle in a salt-free concentrated colloidal suspension. Salt-free suspensions contain charged particles and the added counterions that counterbalance their surface charge. A spherical cell model approach is used to take into account particle-particle electro-hydrodynamic interactions in concentrated suspensions. The finite size of the counterions is considered including an entropic contribution, related with the excluded volume of the ions, in the free energy of the suspension, giving rise to a modified counterion concentration profile. We are interested in studying the linear response of the system to an electric field, thus we solve the different electrokinetic equations by using a linear perturbation scheme. We find that the ionic size effect is quite important for moderate to high particles charges at a given particle volume fraction. In addition for such particle surface charges, both the electrophoretic mobility and the dynamic mobility suffer more important changes the larger the particle volume fraction for each ion size. The latter effects are more relevant the larger the ionic size.   

Modeling the transport of binary fluid/nanoparticle mixtures through microchannels with ciliated walls

We study the dynamic behavior of nanoparticle-filled binary fluids that are driven through a microchannel with ciliated walls. To carry out these studies, we use a hybrid computational approach that combines the lattice Boltzmann model for binary fluids and a Brownian dynamics model for the nanoparticles. The ciliated walls of the microchannels are composed of flexible filaments that are modeled as beads connected by elastic springs. This hybrid model allows us to capture the interactions between the binary fluids, nanoparticles, and the hairy walls. We show that the process of capillary filling of such microchannels strongly depends on the rigidity of the hairs, their grafting density, and their affinity to the fluid components and nanoparticles. We demonstrate that by tailoring the properties of the nanoparticles, one can effectively control not only the velocities of the capillary filling, but also the deposition of nanoparticles on the hairy walls, and hence dynamically alter the properties of these ciliated surfaces. Our findings provide fundamental insights into the dynamics of this complex system, as well as potential guidelines for technological processes involving capillary filling with nanoparticles in a structured flexible porous medium.   

Roles of Low Molecular Weight Amide on Crystallization Behavior of Poly (L-lactic acid)

Organic nucleating agents play an important role in enhancing the crystallization rate of polymers. The aim of this study is to investigate the effect of low molecular weight aliphatic amides on the crystallization behavior and mechanism of poly (L-lactic acid) (PLLA). The crystallization rate of PLLA during non-isothermal crystallization and isothermal crystallization has been significantly improved with the addition of N, N'-ethylenebis (12-hydroxystearamide) (EBH) and/or N, N'-ethylenebisstearamide (EBSA), and EBH exhibits stronger nucleating ability. Time-resolved FTIR spectra illustrate the chain conformational changes and the crystallization kinetics during isothermal crystallization of PLLA mixtures and pure PLLA, especially in the early stages. The formation of interchain conformational-ordered structure and intrachain 103 helix structure for amide-doped PLLA precedes that of pure PLLA, suggesting a stimulatory nucleating effect of EBH and EBSA. In the case of PLLA/EBH, the interchain interactions of -(COC+CH3) and -CH3 groups are faster than the -(CH3+CC) intrachain interactions, while the interchain interactions and the intrachain 103 helix formation are nearly synchronous for PLLA/EBSA, indicating that EBH has an improved effect on the nucleating ability and crystallization kinetics of PLLA, compared to EBSA. The possible mechanism has been discussed, which may be attributed to the hydrogen bond interaction between hydroxyl groups in EBH and the carbonyl groups in PLLA.   

Ion Energy Distribution Studies of Ions and Radicals in an Ar/H$_{2}$ Radio Frequency Magnetron Discharge During a-Si:H Deposition Using Energy-Resolved Mass Spectrometry

Ion energy distributions of sputtered Si particles have been measured by an energy-resolved mass spectrometer, and we correlate the results with measured thin film properties. The plasmas have been generated in a conventional magnetron chamber powered at 150W, 13.56MHz at hydrogen flow rates ranging from 0-25sccm. Various H$_{n}^{+}$, SiH$_{n}^{+}$, SiH$_{n}$ fragments (with n = 1, 2, 3) together with Ar$^{+}$ and ArH$^{+}$ species were detected in the discharge. The most important species for the film deposition is SiH$_{n}$ with n = 0,1,2, and H fragments affect the hydrogen content in the material. The flux of Ar$^{+}$ decreases and that of ArH$^{+}$ increases when the hydrogen flow rate was increased. However both fluxes saturate at hydrogen flow rates above 15sccm. Plasma parameters, such as plasma potential V$_{p}$, electron density n$_{e}$ and electron energy T$_{e}$, are measured with the Langmuir probe. The ion energy distribution (IED) of all prominent species in the plasma is measured with an energy resolved mass analyzer. The plasma parameters decreased with increasing hydrogen flow rate; V$_{p}$, n$_{e}$ and T$_{e}$ decreased from 36.5V, 7.2x10$^{15}$ m$^{-3}$, 5.6eV to 32.8, 2.2x10$^{15}$m$^{-3}$ and 3.8eV respectively. The ion energy of the heavy species, Ar, Ar$^{+}$, ArH, ArH$^{+, }$SiHn and SiH$_{n}^{+}$ radicals have ion energies comparable to the plasma potential. Analysis of the IEDs shows an inter-dependence of the species and their contribution to the thin film growth and properties.   

Calculation of exciton binding energy and electron-hole recombination probability in quantum dots using explicitly correlated electron-hole wavefunction based method

Accurate description of electron-hole correlation plays a central role in describing optical properties of quantum dots. This talk will focus on development of explicitly correlated wavefunction based methods for accurate treatment of electron-hole correlation. In this method, the wavefunction depends explicitly on the electron-hole inter-particle distance (R12) term and electron-hole wavefunction is obtained using variational procedure by minimizing the total energy. In inclusion of R12 term allows for a better description of wavefunction at small electron-hole distances and is found to be crucial for calculation of accurate electron-hole recombination probability and binding energy. The 2-particle electron-hole reduced density matrix (2-RDM) is obtained from the optimized wavefunction and the electron-hole recombination probability is computed from the diagonal elements of the 2-RDM. The developed method is applied to InGaAs/GaAs, CdSe/ZnS, and InP/InGaP quantum dots and exciton binding energy and electron-hole recombination probability are computed for a range of dot sizes. The computed results are compared with experimental results and path-integral Monte Carlo and configuration interaction calculations.   

The Use of Confocal Raman Spectroscopy to Quantitatively Study the Interactions Between Immersive Water and Graphene/Graphene Oxide Surfaces

The unique mechanical, chemical, optical, and electrical properties of graphene allow for many potential applications in biomaterials. Understanding and quantifying the surface interactions between graphene/graphene oxide and aqueous liquid is essential for the design of such graphene-based nanocomposites. Graphene sheets were produced by the mechanical exfoliation of graphite. We have used depth Confocal Raman Spectroscopy (CRM) profiles to measure graphene wettability using a water immersive objective lens, and demonstrated how surface energy between graphene/graphene oxide and immersive aqueous liquid can be affected to simultaneously measure the depth image profiles. Contact angles were also measured to further investigate the compatibility between graphene/graphene oxide and its environment.   

Preparation and anisotropy of large-scale lyotropically aligned functionalized multilayer graphene

Comparing with ballistic electron and phonon transport along graphene sheets, phonon and electron transferring traversing stacked graphene layers are conducted by weak Van der Waals forces and hopping conduction so that inevitably debate mechanical, electrical and thermal properties in ``out-of-plane'' direction. Alignment of graphene sheets can orient covalent chemical bonds in these parallel planes, resulting in a strong anisotropy of the large-scale materials from various graphitic forms with optimized mechanical, electrical and thermal properties. Moreover, systematic characterizations of the anisotropy of the ordered structures are rarely available due to their low profile in thickness directions. Here, conductors with highly ordered lamellar structure in large scale are prepared at room temperature from functionalized multilayer graphene (fMGs) by a lyotropical alignment methodology. Distinct difference in mechanical, electronic and thermal properties between lateral (in-plane) and thickness (out-of-plane) directions of the aligned fMGs indicates a strong anisotropy. Benefiting from the anisotropy, ultrahigh electrical and thermal conductivities in lateral direction are obtained, without aid of any chemical or thermal reduction. The finding facilitates the potential large-scale preparation and application of multilayer graphenes in photonic and electronic components, electrodes for energy collectors, conductive polymeric adhesives and composites.   

Using computational chemistry to understand proton transfer in Green Fluorescent Protein

Green Fluorescent Protein has been studied experimentally by the scientific community for years yet frustratingly little is known about the underlying proton transfer process that produces the green fluorescence. We are trying to elucidate more about this process using Density Functional Theory to prepare and run various calculations on GFP that we compare with kinetics data, Raman and vibrational coherence spectra. I am building a model of wild type GFP that is realistically sized for our computational power, yet still contains key residues that might affect the proton transport process. I will compare my results to those of the E222D GFP mutant. This comparison will allow us to see any differences in energy and normal modes that give insights regarding the proton transfer process. For example, how does it depend on a variety of factors such as temperature, buffer, pH, mutations, etc.? We also plan to examine if the proton transfer propagates through the three donor-acceptor pairs of the ``proton wire'' consecutively versus the three protons on the wire transferring simultaneously. Finally, we will consider how quantum tunneling may be involved in the proton transfer.   

MEST-The quantum space-time explain some questions of quantum mechanics

The probability of displacement and period of wave are the quantum space-time. The paper explain of the two-slit interference and the uncertainty relation. (1) $S=P(r)=P(\lambda)={f^2}$. According to the Benford's law, (2) $T=P(t)=ln(1+\frac{1}{t})={\nu}$. Among it, S: the quantum space, f: the amplitude, r: the displacement, T: the quantum time, t: the period, $\nu$: the frequence, $\lambda$: the wavelength, P(x): the probability function. (3) $E'{\psi}=i{\hbar}\frac{\partial{\psi}}{{\partial}t}$. (4) $m'{\psi}=i{\hbar}\frac{{\partial}{\psi}{\partial}t} {{(\partial}x)^2}$, equation (3) over equation (4), substituting equation (1) and (2) into it, (5) $E'{\psi}=m'{\psi}c'^2=m'{\psi}\frac{({\partial}f^2)^2}{({\partial}\nu)^2}$, getting the energy-wave and mass-wave equation, (6) $E'=i{\hbar}\frac{{\partial}f^2}{{\partial}\nu}$. (7) $m'=i{\hbar}\frac{{{\partial}\nu}}{{\partial}f^2}$. (8) $\Delta{E'}\Delta{\nu}=\Delta{E'}\Delta{t}=i{\hbar}\Delta{f}^2, (\Delta{f}^2\geq\frac{1}{2})$. (9) $\Delta{p'}\Delta{f^2}=\Delta{p'}\Delta{\lambda}=i{\hbar}\Delta{f}^2, (\Delta{f}^2\geq\frac{1}{2})$. Among it, $E'$: the energy of wave, $m'$: the mass of wave, $c'$: the velocity of light, ${\psi}$: the Wave Functions, $f^2$: the probability. Here, the equation (8) and (9) are new uncertainty relation. In the two-slit interference, because (10) $ c'=\frac{\lambda}{t}=\frac{f^2}{t}$, so (11) $ f^2={\lambda}$(the wavelength), so (12) ${\lambda}\geq{d}$( the width of the slits). Measuring the time of light at one slit(1) and its energy at other silt(2) together. And the measuring probability, if (13) $f_1^2\geq\frac{1}{2}, f_2^2\geq\frac{1}{2}, f_1^2=f_2^2, (f_1^2+f_2^2)\leq1$, then (14) $f_1^2=f_2^2=\frac{1}{2}$.   

Initial-state dependence of the quench dynamics in integrable quantum systems

We identify and study classes of initial states in integrable quantum systems that, after the relaxation dynamics following a sudden quench, lead to near-thermal expectation values of few-body observables. In the systems considered here, those states are found to be insulating ground states of lattice hard-core boson Hamiltonians. We show that, as a suitable parameter in the initial Hamiltonian is changed, those states become closer to Fock states (products of single site states) as the outcome of the relaxation dynamics becomes closer to the thermal prediction. At the same time, the energy density approaches a Gaussian. Furthermore, the entropy associated with the generalized canonical and generalized grand-canonical ensembles, introduced to describe observables in integrable systems after relaxation, approaches that of the conventional canonical and grand-canonical ensembles. We argue that those classes of initial states are special because a control parameter allows one to tune the distribution of conserved quantities to approach the one in thermal equilibrium. This helps in understanding the approach of all the quantities studied to their thermal expectation values.   

Many-body physics of optically excited, frozen Rydberg gases

We discuss the many-body physics of an ensemble of optically excited Rydberg atoms with van der Waals dipole-dipole interactions [1]. Starting from a fully quantized model of the optical excitation we show that Rydberg excitations always possess a finite kinetic energy mediated by photon exchange even if the motion of the atoms can be disregarded. The kinetic energy competes with the repulsive vdW interactions. Using discretization and DMRG, we calculate the many-body ground state in the one-dimensional case. It is correlated much more strongly than possible for any local interaction, i.e., with a Luttinger parameter $K \ll 1$. In the presence of an additional lattice, a fractal phase diagram [2] emerges with Mott-insulating phases at any rational filling fraction. [1] see e.g. H. Weimer, R. L\"ow, T. Pfau, and H. P. B\"uchler; Phys. Rev. Lett. 101, 250601 (2008) [2] F. J. Burnell, M. M. Parish, N. R. Cooper, and S. L. Sondhi; Phys. Rev. B 80, 174519 (2009)   

Topological insulators in cold-atom gases with non- Abelian gauge fields: the role of interactions

With the recent technological advance of creating (non)- Abelian gauge fields for ultracold atoms in optical lattices, it becomes possible to study the interplay of topological phases and interactions in these systems. Specifically, we consider a spinful and time-reversal invariant version of the Hofstadter problem. In addition, we allow for a hopping term which does not preserve $S_z$ spin symmetry and a staggered sublattice potential. Without interactions, the parameters can be tuned such that the system is a topological insulator. Using a combination of analytical techniques and the powerful real-space dynamical mean-field (R-DMFT) method, we discuss the effect of interactions and determine the interacting phase diagram.   

Composite-pulse magnetometry in the solid-state

The sensitivity yielded by magnetometry schemes at the quantum level is limited by experimental imperfections in the interrogation pulses and, especially in the solid-state, by relatively short dephasing times. We investigate the use of composite-pulse magnetometry sequences as a means of addressing both limitations. We perform proof-of-principle experiments on magnetometry and noise characterization through a continuous sequence of rotary echoes applied to a single qubit in the nitrogen-vacancy center in diamond. The rotary echo is the simplest unit of a composite pulse sequence, consisting of two consecutive pulses of identical nominal rotation angle applied with opposite excitation phases. Unlike other composite sequences, the rotary echo corrects for excitation field, but not for static field, inhomogeneities. The presented scheme is flexible in that a suitable choice of rotation angle compensates for different scenarios of noise strength and origin (dephasing or fluctuations in excitation intensity). Obtained sensitivities are in the range between those obtained with the widely used Ramsey spectroscopy sequence and the recently implemented method relying on frequency beats in Rabi oscillations.   

Atoms talking to SQUIDs

We present our advances towards a hybrid quantum system of $^{87}$Rb atoms coupled to a superconducting flux qubit through the magnetic dipole transition. We plan to trap atoms in the evanescent field outside a 500 nm nanofiber. This will allow us to bring the atoms less than 5 $\mu$m above the surface of the superconductor without producing excessive heating or changing magnetic fields. As an intermediate step, we plan on coupling the atoms to a superconducting LC resonator. Current progress includes production of nanofibers with $>$98\% transmission, and a tunable high-Q superconducting resonator. Additionally, we show how to use our system as a unified interface for microwave and optical photons, in which the atoms act both as a quantum memory and transduce excitations between the two frequency domains. Using coherent control techniques, we examine conversion and storage of quantum information between microwave photons in superconducting resonators, ensembles of ultracold atoms, and optical photons as well as a method for transferring information between two resonators.   

Nonequilibrium steady state for strongly-correlated many-body systems: a variational cluster approach

The understanding of the nonequilibrium behavior of strongly correlated quantum many-body systems is a long standing challenge, both in theory as well as in experiments. Here, we present a new numerical approach that allows to calculate nonequilibrium steady state properties of strongly correlated quantum many-body systems. The approach is formulated in the framework of Keldysh Green's functions and is based on the ideas of the variational cluster approach (VCA), which has been successfully applied to a variety of strongly correlated many-body systems in equilibrium. As in equilibrium VCA, one crucial aspect appears to be the variational procedure, consisting in a self-consistent adjustment of the equilibrium reference system to the nonequilibrium target state. We apply the presented approach to non-linear transport across a strongly correlated quantum wire described by the fermionic Hubbard model.   

Two dimensional analysis of a free oscillation atom interferometer

In a free oscillation atom Michelson interferometer, a Bose Einstein condensate in the ground state of a harmonic oscillator potential is split by a sequence of laser pulses and then the split wave packets are allowed to undergo a free oscillation. The wave packets are recombined at the splitting location after they make one or more full cycle oscillations. The motion of the wave packets becomes two dimensional if they are misaligned from the axis of the wave guide at the time of splitting. The dynamics of the split condensates becomes more complicated in this situation than a purely one dimensional oscillation. We develop a simple two dimensional model to analyze the effects of a slightly misaligned atomic wave packets on interferometry.   

Exciton-polariton Vortex-Antivortex lattices in two-dimensional hexagonal potential geometries

Microcavity exciton-polariotns possess the duality nature of wave and particle associated with the constituent particles, cavity photons and quantum well excitons. They are quantum bosons in the dilute density limit at low temperatures, exhibiting Bose-Einstein condensation (BEC) as a testbed to explore fundamental nature of physics. In particular, they are confined in two-dimensional plane, where exotic physical phenomena appear. Here, we discuss how to form vortex-antivortex lattices formed by exciton-polariton condensates trapped in two-dimensional hexagonal potential landscapes: triangular-, honeycomb- and Kagome- geometries. This will provide insights to invenstigate the BEC to Berenskii-Kosterlitz-Thouless transition.   

Tunable Spin-orbit Coupling and Quantum Phase Transition in a Trapped Bose-Einstein Condensate

Spin-orbit coupling (SOC), the intrinsic interaction between a particle spin and its motion, is responsible for various important phenomena, ranging from atomic fine structure to topological condensed matter phenomena. While the SOC strength in typical solid state materials is much smaller than the Fermi velocity of electrons, it can reach the same order or even beyond the Fermi velocity of atoms in a recent breakthrough experiment that realizes SOC for ultra-cold atoms. However, the SOC strength in the experiment, determined by the applied laser wavelengths, is not tunable. Here we propose a scheme for tuning the SOC strength through a fast modulation of the laser intensities. We find that tuning SOC strength can drive a quantum phase transition (QPT) from a spin-balanced to a spin-polarized state in a harmonic trapped Bose-Einstein condensate (BEC). The QPT is similar as that in the long-sought Dicke model in quantum optics, which has important applications in quantum information. We characterize the QPT using the periods of collective oscillations (center of mass motion and scissors mode) of the BEC, which show pronounced peaks and damping around the quantum critical point.   

Non-equilibrium spin dynamics in an ultra-cold gas

We study spin dynamics in an out-of-equilibrium quantum gas. Using an optical technique, we imprint arbitrary one-dimensional spin structures in a trapped gas of Rb-87 atoms near quantum degeneracy. These spin structures can exhibit instabilities or lead to spin wave oscillations. The spin system has a highly nonlinear nature, and these spin waves can lead to collapse and revival of coherence. In particular, we measure spin currents in the ultra-cold gas, observe spatially localized collapse and revival of Ramsey fringe contrast, and show how the pattern of coherence depends on the strength of the spin-wave excitation. Lastly, we explore instabilities in the non-equilibrium spin system that can lead to spontaneous amplification of coherence.   

Calculation of BEC transition using the Mathieu equation

While most calculations of the properties of bosons in optical lattices focus on the tight-binding Hubbard model regime, generally the single-particle states of bosons in an optical lattice satisfy the Mathieu equation. We have developed a formalism for studying bosons in an optical lattice using the Mathieu equation. The Mathieu equation formalism provides a natural way to explore physics in regimes where the Hubbard model description breaks down. We use this formalism to compute the momentum distribution of bosons in an optical lattice as probed in time-of-flight expansion, as well as finite size effects and signatures of the phase transition.   

A Theory of BCS-BEC Crossover

In ultracold atomic fermions, the sign and the magnitude of pairing interactions can be controlled by using the magnetically-tuned Feshbach resonances to achieve a continuous transition between Cooper pairs of dilute fermi gas to BEC of diatomic molecules, which is known as the ``BCS-BEC crossover.'' At present, although several models have been proposed, there is still no exact analytical solution of the many-body problem of BCS-BEC crossover region. The standard BCS mean-field theory of superconductivity was used to describe the whole crossover resulting a useful approximation. In our studies, we introduced solvable models for an exact analytical solutions of BCS-BEC crossover region at T = 0 using the generalized SU(2) X SU(1,1) coherent states.   

Boson gas in a periodic array of tubes

We report the thermodynamic properties of an ideal boson gas confined in an infinite periodic array of channels modeled by two, mutually perpendicular, Kronig-Penney delta-potentials. The particle's motion is hindered in the $x$-$y$ directions, allowing tunneling of particles through the walls, while no confinement along the $z$ direction is considered. It is shown that there exists a finite Bose-Einstein condensation (BEC) critical temperature $T_{c}$ that decreases monotonically from the 3D ideal boson gas (IBG) value $T_{0}$ as the strength of confinement $P_{0}$ is increased while keeping the channel's cross section, $a_x a_y$ constant. In contrast, $T_{c}$ is a non-monotonic function of the cross-section area for fixed $P_{0} $. In addition to the BEC cusp, the specific heat exhibits a set of maxima and minima. The minimum located at the highest temperature is a clear signal of the confinement effect which occurs when the boson wavelength is twice the cross-section side size. This confinement is amplified when the wall strength is increased until a dimensional crossover from 3D to 1D is produced.   

Dynamics and evaporation of defects in Mott-insulating clusters of boson pairs

Repulsively bound pairs of particles in a lattice governed by the Bose-Hubbard model can form stable clusters corresponding to finite-size Mott insulators. Here we study the dynamics of hole defects in such clusters corresponding to unpaired particles which can resonantly tunnel out of the cluster into the lattice vacuum. Because of bosonic statistics, the unpaired particles have different effective mass inside and outside the cluster, and ``evaporation'' from the cluster boundaries is allowed only when their quasi-momenta are within a certain range of transparency. We show that quasi-thermalization of hole defects occurs in the presence of catalyzing defects of triple occupied sites which thereby purify the Mott insulating clusters. We study the dynamics of 1D systems, verifying the analytical reasoning by numerically exact t-DMRG simulations. We derive an effective strong-interaction model that enables simulations of the system dynamics for longer times and allows checking with a higher number of defects. We also discuss a more general case of two bosonic species which for equal tunneling rates reduces to the special case of the fermionic Hubbard model in the strong interaction limit, where dynamical purification has been discussed before [2].   

Experimental witnessing of the initial correlation between an open quantum system and its environment

System-environment correlations, which determine the (non-)Markovian character of a dynamical process, is an area of intense interest in the study of open quantum systems. We send photons emitted from a quantum dot sample into a 15-m polarization-maintaining optical fiber to generate different system-environment correlated states and then witness the correlations by observing the growth of trace distances. This experimental scheme of correlation witnessing based on system-environment information flow can also be used for other similar systems.   

Time-dependent Hamiltonian identification

It is demonstrated that the time dependence of the Hamiltonian operator can be extracted by measurement of the evolution operator of the quantum system for a set of control parameters. For the case where the time dependence is weak and can be treated as a perturbation it is possible to express the inversion procedure in an analytic form. In the case of general time dependence, the iterative procedure is developed and its stability is analyzed.   

Open Optomechanical Whispering Gallery Mode Resonators

We have investigated open cavity Whispering Gallery Mode Resonators (WGMR) suitable for optomechanical coupling, and we present our initial demonstrations of structurally modified WGMR using microfabrication techniques. There has been strong interest in WGMR technology due to its extremely high optical quality and its compact robust nature. These monolithic optical resonators offer many advantages over mirror-based Fabry-Perot cavities that typically require special optical coatings. Standard WGMR, however, are constrained because only a tiny portion of the mode volume is externally accessible, limited to the perimeter of the disk where the evanescent field exists slightly outside the resonator. We have applied focused ion beam milling to augment WGMR discs with open structure, which allows direct access to the internal optical fields. By incorporating a mechanical cantilever inside the cavity, the coupled optomechanical system can yield extremely high sensitivity to displacement and acceleration, which would be well suited for miniature accelerometers and gyroscopes. This novel open cavity WGMR scheme could lead to many innovative applications that are unviable within the closed structure of conventional WGMR, including inertial sensors, trace gas detection, and laser sources.   

Local Structural Study of Prussian Blue Analog $Fe_3(Co(CN)_6)_2*nD2O$

The family of Prussian Blue analogs (PBA) is of interest, in part, because a number of them have been shown to exhibit negative thermal expansion. $Fe_3(Co(CN)_6)_2*nH_2O$ is particularly interesting because, when fully hydrated, it has been shown to have both positive and negative thermal expansion in the region from 80-298K while its partially dehydrated form demonstrates a linear-like negative thermal expansion over the same temperature region. To investigate the role local structural properties play in these systems we conducted temperature varying neutron pair distribution function (PDF) analysis on both the fully hydrated and partially dehydrated $Fe_3(Co(CN)_6)_2*nD_2O$.   

Reduced-Density-Matrix Description for Multi-Photon Processes in Quantized Electronic Systems

A reduced-density-matrix description is developed for multi-photon processes in quantized many-electron systems, taking into account environmental electron-photon and electron-phonon interactions. Using a perturbation expansion of the frequency-domain Liouville-space self-energy operator, the spectral-line widths and shifts are evaluated in the isolated-line and short-memory-time (Markov) approximations. Applications of interest include spectral simulations for single-photon and two-photon absorption processes in atomic, molecular, and solid-state systems.   

Ab Initio Calculations for Electronic Relaxations in Molecules and Solids Due to Scattering by Phonons

We carry out first-principles calculations for relaxations of excited electrons in molecules and solids due to scattering by phonons. Density matrix theory (DMT) is employed, which allows for a rigorous evaluation of electronic lifetimes, line widths and shifts, entirely from first principles. The three main ingredients in these calculations -- electronic energy levels, dipole-transition matrix elements, and electron-phonon coupling matrix elements -- are obtained from configuration interaction (CI) and density functional theory (DFT). Combining DMT, CI, and DFT allows one to avoid the use of the empirical line widths, as commonly employed in most previous investigations, and instead calculate their values from first principles. The calculated line widths and shifts are used to construct theoretical linear absorption spectra, which are then compared with experimental results.   

Creation of superposition states in many-body systems by scattering

When quantum systems interact with the environment the interaction typically leads to decoherence of the system's quantum state. Here we show that one mechanism of interacting with the environment---uncontrolled scattering of probe particles by a many-body system---can instead lead to coherent superpositions of the system particles. For a system of two particles scattering leads to relative localization of the particle positions, while for more than two particles the system particles localize relative to one another in a pairwise fashion allowing superpositions in position space. We simulate scattering and the creation of these superposition states for many-body systems in free space and trapped in optical lattices. The different superpositions created are signaled in the scattering distributions and could be detected by allowing the particle wavefunctions to expand and interfere.   

Analysis of Low-Z EUV Spectra from ``Sparky'' Laboratory Plasma Experiments

This study provides an analysis of recent experimental EUV and soft X-ray laser plasma spectra from the compact laser facility ``Sparky'', generated under various plasma conditions. The developed non-LTE kinetic models of low-atomic number elements, such as C, O, F, etc., based on the Flexible Atomic Code data, are utilized . By matching the features of experimental spectra to the predictions of our atomic and plasma models, whose parameters are studied and precisely specified, the conditions of source plasmas can be inferred. The emitted EUV radiation we examine generally falls in the 90 {\AA} to 260 {\AA} wavelength range. In addition, the most intense lines from He-like ions of C and O in the soft X-ray region (20 {\AA} - 40 {\AA}) are observed. The most diagnostically significant temperature and density sensitive spectral lines are identified and proposed to use in plasma diagnostics for various applications including fusion research. This work is supported by DOE under grant DE-FG02-08ER54951.   

Smart Combinatorial Research Equipment (SmartCoRE) for Sample Environmental Control and Automated Analysis with Optical Methods

Combinatorial research (CR) has revolutionized the way research is done in every major chemistry, physics and material science laboratory. We propose to bring the same success of automation and capabilities of CR to a widely used technique, small- and wide- angle x-ray scattering (SAXS/WAXS) through our development of a small, modular sample environmental chamber with embedded control electronics that can easily be used in large arrays. The device however is not restricted to a SAXS/WAXS techniques as it can easily be adapted to almost any kind of small volume sample prep or optical analysis technique requiring control of basic sample environmental parameters such as temperature, atmosphere, light and electromagnetic fields. The prototype has the following capabilities: 1. Automated switching of external electronic instrumentation between modules. 2. Thermoelectric temperature control from -50 to 200 C. 3. Ports for gas flow through or evacuation of sample environment. 4. Sealed sample environment using minimally scattering window material. 5. 90 degree field of view of both sides of sample. 6. Optional fiber-optic connections for UV-Vis spectroscopy. 7. Optional GISAXS mounting geometry. 8. Optional liquid sample flow cell.   

Non-Perturbative and Moments Methods Applied to the Morse Potential

The well-known Morse potential has been well known to both physicists and quantum chemists for a number of years and has been used to model the behavior of diatomic molecules. Explicitly it may be written as% \[ V(r)=D_{e}\left( e^{-2a\left( r-r_{e}\right) }-2e^{-a\left( r-r_{e}% \right) }\right) +D_{e}% \] where $r$ is the inter-atomic separation, $r_{e}$ is the (equilibrium) bond length and $D_{e}$ is the depth of the potential well. The width of the well is given by $a^{2}=k_{e}/2D_{e}$ with $k_{e}$ the effective spring constant. Here we wish to study both the ground state energy (using both the Connected Moments Expansion and the Generalized Moments expansion) as well as the entire spectrum using a Lanczos scheme. Our results will be compared with other well-established results.   

Low Frequency Perturbations, Adiabatic Ground States and Wave Function Collapse

It is a well known and established fact that Time Dependent Perturbation Theory (TDPT) predicts that non- resonant time dependent perturbations will provoke no change in the excited state probability amplitudes of quantum systems. In this work we study a number of quantum systems wherein, at low frequencies, a response is indeed generated (by non-resonant perturbations) causing the system to respond adiabatically and hence resulting in the creation of instantaneous (time-dependent) ground states. These instantaneous time-dependent ground states are a linear combination of both the ground state and the excited states. The wave-function collapse of these adiabatic ground states calls into question the common wisdom that off-resonant perturbations can have no effect on quantum systems.   

Topologically Protected Quantum State Transfer in a Chiral Spin Liquid

Topology plays a central role in ensuring the robustness of a variety of physical phenomena. Notable examples range from the robust current carrying edge states associated with the quantum Hall and the quantum spin Hall effects to proposals involving topologically protected quantum memory and quantum logic operations. In this talk, I will describe a topologically protected channel for the transfer of quantum states between remote spin-based quantum registers. In our approach, state transfer is mediated by the edge-mode of a chiral spin liquid. I will demonstrate that the proposed method is intrinsically robust to realistic imperfections associated with disorder and decoherence. Possible experimental implementations and applications to the detection and characterization of spin liquid phases will be discussed.   

Landau-Zener-St\"uckelberg Interference of Microwave Dressed States in a Superconducting Phase Qubit

Landau-Zener-St\"uckelberg (LZS) interference is a well-known quantum phenomenon in a variety of physical systems, including atoms and solid-state systems. However, all the previous works were performed in simple systems having avoided level crossings in their energy diagrams. From both theoretical curiosity and practical significance it is important to know whether LZS interference can be observed in the dressed states, usually generated from the interaction between photons and atoms. We present the observation of LZS interference of the dressed states arising from a macroscopic quantum object, a superconducting phase qubit, interacting with a microwave field. The dependence of LZS interference fringes on the microwave power, microwave frequency, and the initial state of the qubit agrees quantitatively very well with the theoretical prediction. Such LZS interferometry involving the dressed states enables us to control the quantum states of multipartite systems with ease. In fact, this method is applicable to ANY quantum systems, which have avoided level crossings resulting from interaction between the individual constituents and photons.   

Switching Phenomena in Bifurcation Amplifiers

Recent experiments have seen high fidelity single shot measurement of superconducting qubits using the latching readout of a bifurcation amplifier. In these measurements, the coupling of the qubit to a nonlinear resonator correlates the qubit state with bistable states of the resonator. So qubit state discrimination, and hence readout quality, is ultimately governed by the dynamics of switching between the resonator states. In order to investigate how the quality of the measurement depends on system parameters, we study the physical mechanism of this probabilistic switching between the bistable resonator states. Recent simulations have shown that the switching rate can be very accurately obtained from a quantum trajectory model of the dynamics. We study Arrhenius formulae to model the switching rate and look to a Gaussian variational solution to the trajectory equations in order to gain an improved qualitative picture of the dynamics of these switching events.   

Towards Realization of a Tunable Josephson Superinductor

Many Josephson circuits intended for quantum computing would benefit from the realization of the Josephson ``superinductor'': a phase-slip-free element whose inductive impedance at the plasma frequency exceeds the quantum of resistance, $h/(2e)^2$. With this aim, we have fabricated a chain of cells whose Josephson coupling can be frustrated by the magnetic field. These asymmetric dc-SQUID-like cells have several large Josephson junctions (JJs) in one arm shunted by a single small JJ in the other arm. The phase slips in this chain are suppressed by the phase rigidity across larger JJs, which remains strong even when the cell is frustrated by the magnetic field (while its Josephson inductance increases). Numerical simulations which explicitly take into account quantum fluctuations were used to optimize the JJ parameters. The inductance and phase rigidity of the device was probed by measuring the microwave response of the array coupled to a lumped-element microwave resonator. The resonance frequency of this circuit, $f_r$, and its quality factor Q were measured as functions of the magnetic field B. The observed dependences $f_r(B)$ and $Q(B)$ which reflects the variations of the Josephson inductance and phase rigidity of the array, will be compared with numerical simulations.   

Collective Phenomena in a Capacitively-Coupled Transmon Array

The manifestation of condensed matter physics phenomena in interacting photon systems has been of recent theoretical interest. Under the circuit quantum electrodynamics (cQED) architecture, light-matter interactions can be engineered into a strong coupling regime and many-body interacting photon systems can be fabricated. In this experiment, we create a triangular array of 100 niobium transmon qubits on a sapphire substrate. Photon-mediated interactions are facilitated through capacitive coupling among the transmons, each with a charging energy of approximately 200MHz. Collective quantum behavior of the josephson-junction array is explored by measuring transmission across the array through input-output ports on the device itself as well as through a 3D cavity. This experiment is an important step towards realizing many-body, interacting quantum phenomena with photons.   

Compact superconducting coplanar microwave beam splitters

The recent evolution of circuit quantum electrodynamics with standing-wave microwave modes towards setups for propagating quantum microwaves has triggered the need for low-loss superconducting microwave beam splitters. Such a device should have ports obeying the coplanar geometry relevant for circuit QED and, at the same time, be compact for the sake of scalability. This combination presents a serious challenge. In this work, we present an experimental characterization of various compact superconducting coplanar microwave beam splitters. In addition, we briefly discuss efforts towards a tunable beam splitter.   

Design and measurement of a silicon double quantum dot qubit with dispersive microwave readout

The electronic states of a semiconductor quantum dot are a promising candidate for quantum information processing. We describe a circuit QED qubit architecture in which a semiconductor qubit in silicon is capacitively coupled to a 6 GHz superconducting resonator. Silicon is an attractive material on account of the long electron spin lifetime. We discuss the design and operation of both the laterally defined double quantum dot qubit as well as the balanced coplanar stripline resonator.~~We focus in particular on the chip design and the specifics of the measurement setup, including both low and high frequency filtering. We also discuss the possibility of operating this device as a spin qubit by way of applying an inhomogeneous magnetic field.   

Improved rf-SSET Performance using On-Chip Superconducting LC Matching Networks on Si/Ge

The radio-frequency superconducting single electron transistor (rf-SSET) has been demonstrated to be a nearly quantum-limited charge sensor [1]. Building upon previous successful coupling of an aluminum SSET in the vicinity of quantum dots (QDs) on Si/SiGe using an off-chip inductor [2], we now developed on-chip matching networks to improve the charge sensing of Si/SiGe double quantum dots. Here, we report measurements in superconducting rf-SSETs, where the SET is directly fabricated with an on-chip inductor, giving enhanced sensitivity at our operating temperature of 0.3K. Recent experimental results including the investigation of the range of in-plane magnetic field compatible with RF-SET operation will also be discussed. \\[4pt] [1] W.W.Xue et al, Nature Phys. 5, 660 (2009);\\[0pt] [2] M.Y.Yuan et al, Appl. Phys. Lett. 98, 142104 (2011)   

Observable measure of quantum correlations

The correlations of multipartite quantum states have nonclassical features that go beyond entanglement. A full theoretical and experimental characterization of these features is necessary to understand their foundational role in quantum theory, and to explore the usefulness of such nonclassical resources for quantum computation and communication. We introduce a measure of general bipartite quantum correlations for arbitrary two-qubit states, expressed as a state-independent polynomial function of the density matrix elements. The amount of quantum correlations can be quantified experimentally by measuring the expectation value of a small set of observables on up to four copies of the state, without the need for a full tomography. We extend the measure to 2 x d systems, providing its explicit form in terms of observables for the relevant class of multiqubit states employed in the DQC1 model for quantum computation. Finally, we study the evolution of quantum correlations between two qubits embedded in a bosonic bath, showing that our measure can reliably identify the transition between weak and strong system-environment coupling regimes. This leads us to propose an experimentally friendly signature of non-Markovianity based on quantum correlations dynamics.   

New Families of Coherent States for the Supersymmetric Oscillator

Supersymmetry is a viable theoretical framework to provide a unified picture of fermionic and bosonic fields. The subjacent supersymmetric algebra intrinsically transforms bosonic degrees of freedom into fermionic ones and vice-versa. Aside from physical realizations, the mathematical objects of supersymmetry (e.g. superspace, supertransformations) have proved fruitful for solving quantum problems based on the concept of partner Hamiltonians. The harmonic oscillator has been extensively studied in this context; a result of particular interest is the vanishing zero-point energy. The supercoherent states were first introduced 25 years ago [1], defined as eigenstates of a generalized annihilation operator that mixes fermionic and bosonic degrees of freedom. Here we extend that original annihilation operator to a family of complex 3-parameter annihilation operators. Our presentation shows the properties of those new operators as well as the properties of the corresponding eigenstates. In particular, after explicitly calculating the eigenstates in parameter space, we present a subspace with bounded uncertainty, for both the Heisenberg and entropic formulations of uncertainty. [1] Supercoherent States, C. Aragone and F. Zypman, Published in J. Phys. A 2267 (1986)   

Room-temperature solid-state quantum memory using pairs of nuclear spins in diamond

We propose a robust, room-temperature solid-state quantum memory scheme using a pair of nuclear spin impurities in diamond. The memory qubit is encoded in a decoherence-free subspace of this nuclear spin pair, which protects it from noise originating from the surrounding environment. In addition, nuclear spins close to a Nitrogen-Vacancy (NV) color center experience a significant electron-mediated coupling, which further suppresses decoherence of the qubit. We obtain coherence times on the order of a second, along with fast manipulation and readout through the coupling of the nuclear spins to the NV electronic spin. We show that through engineering of the diamond sample this scheme could offer scalability to a many-qubit memory, and could be used as a basic building block for hybrid quantum networks and quantum computing architectures.   

Novel quantum behavior generated by traveling across a quantum phase transition

We report novel dynamical behavior in a multi-qubit--light system described by the Dicke model, which is being driven across its thermodynamic quantum-phase boundary. Analyzing the system's quantum fidelity, we find that the near-adiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is the starting point. Depending on the quenching regime a highly non-trivial behavior emerges in both the qubit and radiation subsystems. For the former, we find that for some paths in parameter space the final fidelity of the near-adiabatic process does not depend on the direction of the trajectory, but depends only on the {\it speed} at which the path is traveled. This behavior is contrasted with Landau-Zener tunneling and the Kibble-Zurek mechanism. Furthermore, for some qubit subsystems, we identify purification and screening effects which could be used for quantum control. By contrast, the evolution of the Wigner function shows the radiation subsystem exhibits the emergence of complexity and non-classicality. These findings could be experimentally tested in several condensed matter scenarios -- for example, diamond-NV centers and superconductor qubits in confined radiation environments.   

Exploring the Nitrogen-Vacancy center as a high resolution magnetometer

New schemes that exploit the unique properties of NV centers in diamond are presently being explored as a platform to high resolution magnetic sensing [1, 2]. First we focus on the ability of a NV center to monitor a set of adjacent nuclear spins. For this purpose, we conduct comparative experiments where the NV spin evolves under the influence of surrounding $^{13}$C nuclei or, alternatively, in the presence of asynchronous AC fields engineered to emulate bath fluctuations [3]. Our study reveals substantial differences that underscore the limitations of the semi-classical picture when interpreting and predicting the outcome of experiments designed to probe small nuclear spin ensembles. In particular, our study sheds light on the role of bath fluctuations in the response of NV centers to common pulse sequences, and explores a detection protocol designed to probe time correlations within the random nuclear spin dynamics. Further, we show that the presence of macroscopic nuclear spin order is key to the emergence of traditional spin magnetometry. [1] J. R. Maze, et al., Nature 455, 644 (2008). [2] A. Laraoui, J.S. Hodges, C.A. Meriles, Appl. Phys. Lett. 97, 143104 (2010). [3] A. Laraoui, J. S. Hodges, C. A. Ryan, and C. A. Meriles, Phys. Rev.B 84, 104301 (2011).   

High dynamic range diamond magnetometry for time dependent magnetic fields

Nitrogen-Vacancy (NV) centers in diamond have become a topic of great interest in recent years due to their promising applications in high resolution nanoscale magnetometry and quantum information processing devices at ambient conditions. We will present our recent progress on implementing novel phase estimation algorithms with a single electron spin qubit associated with the NV center, in combination with dynamical decoupling techniques, to improve the dynamic range and sensitivity of magnetometry with time-varying magnetic fields.   

Optical Control of Nuclear Spin Ensembles in Diamond

We present new results on the hyperpolarization of $^{13}$C nuclear spins in diamond through optically-oriented nitrogen vacancy (NV-) defects. Optical illumination of high NV- concentration diamonds at cryogenic temperatures and 9.4 Tesla results in a negative nuclear spin temperature with measured bulk-average polarization over 5$\%$, although local polarization may be higher. The negative spin-temperature is attributed to a population inversion within the dipolar energy levels of the NV- spin ensemble. In our quantitative model, nuclei near defects equilibrate with the NV- dipolar energy reservoir and polarization is transported to the bulk material via spin diffusion. This model is tested by investigating a series of samples with varied defect density. We also investigate the nuclear hyperpolarization of NV- containing diamond nanocrystals. Such materials may be useful for surface transfer of polarization to target molecules for enhanced NMR sensitivity. Additionally, we investigate the dynamics and decoherence of the hyperpolarized nuclear spin ensemble and its interaction with electronic defect spins. Such phenomena are of fundamental interest to the use of diamond for quantum information applications.   

Thwarting the Photon Number Splitting Attack with Entanglement Enhanced BB84 Quantum Key Distribution

We develop an improvement to the weak laser pulse BB84 scheme for quantum key distribution, which utilizes entanglement to improve the security of the scheme and enhance its resilience to the photon number splitting attack. This protocol relies on the non-commutation of photon phase and number to detect an eavesdropper performing quantum non-demolition measurement on number. The potential advantages and disadvantages of this scheme are compared to the coherent decoy state solution. Most entanglement based quantum key distribution schemes rely on violations of Bell's inequalities to ensure security. However, this is not the strategy that our entanglement enhanced (EE) BB84 employs here. Instead, we detect Eve by introducing an entangled quantum state into the system that is sensitive to Eve's QND measurements. This allows for a recovery of an approximately linear dependence on transmittivity for the key rate. EE BB84 shares this advantage with coherent decoy state protocols as well as schemes that utilize strong phase reference pulses to eliminate Eve's ability to send Bob vacuum signals.   

Efficient quantum communication under collective noise

We propose a novel communication protocol for the transmission of quantum information via quantum channels subject to collective noise. Our protocol makes use of decoherence-free subspaces in such a way that an optimal asymptotic rate of transmission is achieved, while at the same time encoding and decoding operations can be implemented efficiently. In particular, for a quantum channel whose collective noise is associated with a discrete group, $G$, i.e.~with a discrete number, $|G|$, of possible noise operators, our protocol achieves perfect transmission at a rate of $m/(m+r)$, where $r$ is a finite number of auxiliary systems that depends solely on the channel in question. In the case where the collective noise of the channel is associated with a continuous group, such as a collective phase noise channel, our protocol leads to efficient, approximate transmission of quantum data with arbitrarily high fidelity and optimal transmission rate. The coding and decoding circuit of our protocol requires a number of elementary gates that scale linearly with the number of transmitted qudits, $m$, in contrast to the best known protocols utilizing a decoherence-free subspace.   

Continuous-Variable Quantum Key Distribution using Thermal States

We consider the security of continuous-variable quantum key distribution using thermal (or noisy) Gaussian resource states. Specifically, we analyze this against collective Gaussian attacks using direct and reverse reconciliation where both protocols use either homodyne or heterodyne detection. We show that in the case of direct reconciliation with heterodyne detection, an improved robustness to channel noise is achieved when large amounts of preparation noise is added, as compared to the case when no preparation noise is added. We also consider the theoretical limit of infinite preparation noise and show a secure key can still be achieved in this limit provided the channel noise is less than the preparation noise. Finally, we consider the security of quantum key distribution at various electromagnetic wavelengths and derive an upper bound related to an entanglement-breaking eavesdropping attack and discuss the feasibility of microwave quantum key distribution.   

Interaction Free Measurement of Quantum Systems

A measurement of the state of a physical system always causes some degree of disturbance in the system. When the scaling consists of nano or smaller quantities, measurements can cause severe changes in the information contained in the system. Noteworthy are the quantum computing elements, or qubits, used operationally and as memory. The main and foremost concern for the quantum computing elements is decoherence which is exacerbated by the measuring process. We propose to overcome these obstacles using an intriguing quantum mechanical interaction free measurement (IFM) method. High-efficiency IFM has been demonstrated by combining quantum interference and the quantum Zeno effect [P. G. Kwiat, et al., Phys. Rev. Lett. 83, 4725 (1999)]. In addition, IFM can be useful for quantum information processing, because it eliminates photon absorbing/scattering processes, which often are responsible for undesired information loss and decoherence in neighboring atoms. This is manifested in optical lattices, dephasing of proximal nuclear spins of nitrogen-vacancy centers in diamond, etc. We further propose and investigate using IFM to replace conventional optical readouts for specific quantum systems with the advantage of elimination of undesired decoherence.   

Spatial entanglement in two-electron atomic systems

Recently, there have been considerable interests to investigate quantum entanglement in two-electron model atoms [1, 2]. Here we investigate quantum entanglement for the ground and excited states of two-electron atomic systems using correlated wave functions, concentrating on the particle-particle entanglement coming from the continuous spatial degrees of freedom. We use the two-electron wave functions constructed by employing $B$-spline basis to calculate the linear entropy of the reduced density matrix $L=1-Tr_A (\rho _A^2 )$ as a measure of the spatial entanglement. Here $\rho _A =Tr_B (\left| \varphi \right\rangle _{AB} { }_{AB}\left\langle \varphi \right|)$ is the one-electron reduced density matrix obtained after tracing the two-electron density matrix over the degrees of freedom of the other electron. Here, we investigate spatial entanglement for two-electron systems with $Z$=1 to $Z$=10. When $Z$ is decreased from $Z$=1.0 to about $Z \mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $ 0.911, the H$^{-}$ ion becomes unbound. This would lead in a situation of one electron bound by the nucleus with the other electron being free. Such a wave function would be expected to have a spatial entanglement of $L $= 1/2. Numerical results will be presented at the meeting. \\[4pt] [1] J. P. Coe and I. D'Amico, \textit{J. Phys.: Conf. Ser.} \textbf{254}, 012010 (2010) \\[0pt] [2] D. Manzano \textit{et. al.}, \textit{J. Phys. A: Math. Theor.} \textbf{43}, 275301 (2010)   

Delayed Choice with Haunted Quantum Entanglement for Choosing at a Distance an Overall Distribution Exhibiting Either Which-Way Information or Interference

Particles 1 and 2 are entangled at one of two possible locations (providing which-way info). The entangled particles physically separate from each other where one particle [P1] preserves the ww information that accompanied entanglement and the other particle's motion [P2] supports interference in P2's overall distribution due to the device setup. With this step, P1 now supplies which-way info to P2 due to their entanglement. Next, there is a delayed choice at a distance. Choice A: P1 and the ww info it carries are essentially lost by releasing many other particles of similar character to P1 into the container with P1 before P2 is detected and before ww info for P1 becomes available to the environment or an irreversible ww measurement is made on P1. (The entanglement is then lost and so is the ww info supplied by P1 to P2.) Choice B: P1 that carries ww info is not lost. (The entanglement is not lost and neither is the ww info P1 has supplied to P2.) Repeat runs of method with choice A 100 times consecutively to develop an overall interference distribution pattern for P2, or instead repeat runs of method with choice B 100 times consecutively to develop an overall ww distribution pattern for P2.   

Full counting statistics and entanglement in a disordered free fermion system

The Full Counting Statistics (FCS) is studied for a one-dimensional system of non-interacting fermions with and without disorder. For two $L$ site translationally invariant lattices connected at time $t=0$, the charge variance increases logarithmically in $t$, following the universal expression $\langle \delta N^2\rangle \approx \frac{1}{\pi^2}\log{t}$, for $t$ much shorter than the ballistic time to encounter the boundary, $t_{b} \sim L$. Since the static charge variance for a length $L$ region is given by $\langle \delta N^2\rangle \approx \frac{1}{\pi^2}\log{L}$, this result reflects the underlying relativistic or conformal invariance and dynamical exponent $z=1$. With disorder and strongly localized fermions, the variance is also found to increase logarithmically in time, but saturates at times $t \approx t_d \propto L^2$, a diffusive time scale. Despite the fact that 1-d fermions are fully localized for any disorder strength, the entanglement responsible for charge fluctuations appears to propagate with dynamical exponent $z=2$.   

Excitation and entanglement dynamics of light harvesting complex II B850 ring

The electronic excitation and the entanglement dynamics between the chromophores of photosynthetic harvesting complex II (LHCII) B850 ring have been studied and analyzed theoretically. Since the coupling energy between the adjacent chromophore electronic excitation is comparable to the bath organization energy, the modified scaled hierarchical equation of motion (HEOM) approach is implemented to treat the whole system in an intermediate coupling regime. Comparing our results to the well-studied Fenna-Matthews-Olson (FMO) protein, we found that quantum coherence of electronic excitation between chromophores also exist in this system at the same temperature level (77K), which also suggests that the excitation energy transfer coherently through the B850 ring instead of incoherent hopping. The calculation of bipartite entanglement between chromophore electronic excitation shows the existence of a long-lived entanglement in this system, illustrates that this kind of quantum effect could survive even in such a noisy environment.   

Tuning the entanglement for a two-dimensional magnetic system with anisotropic coupling and impurities

We study a set of localized spins coupled through exchange interaction and subject to an external magnetic field. For such a class of two-dimensional magnetic systems, we introduce two impurities, and treat as the source, while the rest as the environment bath. It is demonstrated that entanglement can be controlled and tuned by varying the anisotropy parameter $\gamma$, the ratio of magnetic field $h$ and exchange interaction $J$ in the Hamiltonian and three different exchange interaction strengths: $J$ (between environment spins) , $J'$ (impurity - impurity) and $JJ'$ (between impurities and environment), respectively.   

Decoherence and Quantum Walks under the regime of weak measurements and weak values

Our research on Quantum Walks under the regime of quantum weak measurements and weak values (QWWM) is being continued from the perspective of quantum algorithms. Previously we investigated several statistical measures of a QWWM on an infinite line, and did some comparative study of such results with corresponding classical and quantum walks position probability distributions and statistical measures. Now we are interested to show the entanglement and decoherence effects of QWWM. We show preliminary results with respect to how the performance of Grover's algorithm is affected by entangled qubits when decoherence happens due to temperature difference. Furthermore, we provide a physical interpretation of such decoherence of the QWWM so that our results could have some useful applications in the area of quantum information.   

Perfect mixed state quantum transport in correlated spin networks

Spin-based quantum networks form an attractive physical setting for quantum information processing and simulation. We consider the transport of quantum states in arbitrarily large and complex spin networks, with applications to distributed quantum computing. Specifically, we consider transport through spin networks in the mixed-state, since they are the least experimentally demanding to produce in high-temperature laboratory settings. We analyze conditions on the interaction and propagators that allow perfect state transfer in such networks. We show that when there is more than one possible transport path through the network, it is necessary to phase correlate the transport processes occurring along each path. We provide a modified isotropic XY-Hamiltonian that achieves this correlation, and use it to derive engineered couplings for perfect transport in complicated network topologies. Finally, we show that this Hamiltonian can perfectly transfer mixed states, even in arbitrary networks, as long as the spins between which the transport occurs are weakly coupled to the remaining spins.   

APL simulation of Grover's algorithm

Grover's algorithm is a fast quantum search algorithm. Classically, to solve the search problem for a search space of size N we need approximately N operations. Grover's algorithm offers a quadratic speedup. Since present quantum computers are not robust enough for code writing and execution, to experiment with Grover's algorithm, we will simulate it using the APL programming language. The APL programming language is especially suited for this task. For example, to compute Walsh-Hadamard transformation matrix for N quantum states via a tensor product of N Hadamard matrices we need to iterate N-1 times only one line of the code. Initial study indicates the quantum mechanical amplitude of the solution is almost independent of the search space size and rapidly reaches 0.999 values with slight variations at higher decimal places.   

Non-Markovian finite-temperature two-time correlation functions of system operators of a quantum Brownian motion model

We evaluate the non-Markovian two-time correlations (CF's) of system operators of a quantum Brownian motion (QBM) model in two different ways, one by the exactly solvable Heisenberg equation of motion through fluctuation-dissipation theorem and the other by the projection operator technique through the perturbative time-convolutionless non-Markovian effective master equation. In Markovian case, a famous procedure to compute two-time CF's of system operators in open quantum systems is the quantum regression theorem (QRT). However, the QRT is not valid or needs corrections in the non-Markoian domain even in the weak system-bath coupling regime. The calculated non-Markovian two-time CF's up to fourth order in system-environment coupling strength agree well with those obtained from exact evaluation in the weak and mediate coupling regime, which demonstrates the validity of our derived non-Markovian evolution equations. But, the exact analytical two-time CF's for an Ohmic bath presented in the literature are only for the initial time t2 being in the steady state (t2$\to \infty )$, i.e. at equilibrium. Our evolution equations of the non-Markovian two-time CF's are, however, valid for any initial time t2 For a finite initial time t2, considerable difference in the non-Markovian CF's between the fourth-order system-bath coupling case and its second order counterparts can be observed. These results obtained using our derived non-Markovian evolution equations differ significantly from the Markovian case obtained using the QRT and from the non-Markovian case obtained directly using the QRT.   

Combatting decoherence in OAM states due to turbulence

Photons have always been the information carriers of choice in quantum information, with many protocols taking advantage of the polarization degrees of freedom to encode quantum information. Exploiting the photon's orbital angular momentum (OAM) can provide distinctive advantages. The main one is an increased alphabet size for information transmission. Since the Hilbert space of OAM states is infinite dimensional, it can be used to encode more than one bit (or qubit) per photon. However, this potential can only be realized if suitable quantum information can be encoded in the OAM photon states, and if it can be protected from the decohering effect of atmospheric turbulence. In this work, we will numerically simulate the effects of turbulence (using the Kolmogorov model) on photons with a certain value of OAM and how to protect them from the decoherence caused by the atmospheric turbulence.   

Average quantum tunneling times for asymmetric potentials

We generalize a recent definition of average quantum tunneling times, using the Salecker-Wigner-Peres (SWP) clock, to be applicable to the tunneling of a localized wave packet through asymmetric potentials. We investigate the properties of the average transmission and reflection times, including their interpretation in the framework of the weak measurement theory, and compare them with other standard average times. Finally, we discuss the advantages of the definition of average tunneling times as prescribed by the SWP clock (such as the non-saturation of the transmission time for opaque barriers).   

A Modified Special Relativity Theory in the Light of Breaking the Speed of Light

In the OPERA experiment the neutrino broke the speed of light. It moved with speed greater than the highest speed in the universe (the speed of light in vacuum) according to the special relativity [32]. This experiment if it is confirmed will contradict the main basis that the special relativity built on which is the constancy of speed of light, and no particle or electromagnetic wave can exceed this speed [37]. Quantum tunneling experiments have shown that the signal moving superluminal [1-9]. In this work (the modified special relativity theory), we will unify the special relativity theory and quantum theory (Copenhagen school) in concepts, principles and laws. While this new theory is in agreement with the concepts, principles and laws of the quantum theory (Copenhagen school), and it introduces some changes in the concepts, principles and laws of quantum to be descriptive, and imaginative. Quantum theory was applied to the micro world, while the macro world was controlled by the laws of classical physics. In my paper I believe that the theory that controls the micro and macro worlds are the same.   

Relativistic tunneling times for Gaussian wave packets

We investigated an average tunneling time, as suggested by the Salecker-Wigner-Peres clock, for a localized particle described by the Dirac equation. Then we evaluate this average transmission time for a Gaussian wave packet incident on a square barrier. It was found that the time does not saturate for large barriers, that is, the average time doesn't suffer from the Hartmann effect. We also consider the contribution of the negative energy components of the localized wave packet for the average time.   

Wheeler thought experiment with delayed choice

This is an alternative interpretation of Jacques, et. al. (2007), Wheeler's thought experiment with delayed choice. The researchers find that the choice of observables changes the previous behavior of the photon inside the interferometer. Stepping outside the QM box, we propose that elementary waves from the detectors travel backwards through the interferometer, and the photon is following such a ray in the reverse direction. Thus a change in observables changes the behavior of the photon for the simple reason that the observable is transmitting information to the photon and the photon is able to change its polarization mid-stream in response to a change in that information. According to this explanation there is no delayed choice. It is an illusion.   

Measurement of the Depression of the Velocity of Focused Beams of Light with a Gouy-Phase Interferometer

An apparatus is demonstrated that was constructed to show the depression in group velocity $v_g $ of a focused Gaussian (HeNe laser) beam, and arguments presented for the effects of this demonstration on the theoretical basis of Special Relativity. An exploration is conducted of Einstein's theoretical underpinnings for Special Relativity, that light pulses travel at a fixed group velocity $v_g =c$. This is accompanied by theoretical proof that $v_g $ for a focused Gaussian beam is depressed upon focusing, if the beam has a frequency-independent radius, related to the Gouy phase shift. An account of the operation of the apparatus is presented, and data from the operations related, verifying the change in $v_g $. This contradiction of Einstein's assumption, without effect on the experimental validity of Special Relativity, is reconciled by referring to Poincar\'{e}'s derivation of Special Relativity's equations, which assumes simply that Maxwell's equations retain their form across inertial reference frames.   

Amphiphilic Peptide-Polymer Conjugates with Side-Conjugation

As an emerging family of soft matter, peptide-polymer conjugates are highly promising for the design of functional materials. The fundamental understanding of the effect of the interaction between peptides and polymers on the structural and functional properties of these materials is crucial for their development into technologically relevant materials. We have designed a family of amphiphilic materials based on polymer conjugates of coiled-coil helix bundle and characterized their self assembly in surfactant containing aqueous solution. Conjugation of two hydrophobic polymers, PS and PMMA to the exterior of bundle led to unfolding of helix and the extent of structural retention was dependant on polymer hydrophobicity. However, the deleterious effects of hydrophobic polymers on the peptide structures can be eliminated on adding organic solvent to solubilize the hydrophobic polymers. To understand the importance of polymer hydrophobicity, conjugates of the peptide with PNIPAM, which exhibits temperature controlled hydrophobicity, have been studied and the results underscore the significance of the hydrophobic interaction between the polymer and the peptide on the structural retention of peptide. These fundamental studies signify the importance of maintaining the balance between different competitive intermolecular interactions on the peptide structure in these hybrid materials.   

Carbon nanotubes synthesized by pulsed laser deposition for light harvesting devices

A large-area vertically aligned carbon nanotubes (CNTs) have been fabricated by catalyst-assisted pulsed laser deposition techniques on indium tin oxide (ITO) glass substrates. The CNTs have a uniform shape and length, aligned vertically on the surface of the ITO substrates and the average diameter is about 8 nm. The long-term field emission current stability of the CNTs has also been investigated. No obvious current density decay was observed after 15 days continuous experiments, indicating the super stability of the sample. A highly stable, cheap and nontoxic material which can be used as electrodes in dye-sensitized solar cells was obtained.   

Thermodynamic curvature measures interactions

Thermodynamic fluctuation theory originated with Einstein who inverted the relation $S=k_B\ln\Omega$ to express the number of states in terms of entropy: $\Omega= \exp(S/k_B)$. The theory's Gaussian approximation is discussed in most statistical mechanics texts. I review work showing how to go beyond the Gaussian approximation by adding covariance, conservation, and consistency. This generalization leads to a fundamentally new object: the thermodynamic Riemannian curvature scalar $R$, a thermodynamic invariant. I argue that $|R|$ is a thermodynamic measure of the correlation length and suggest that the sign of $R$ corresponds to whether the interparticle interactions are effectively attractive or repulsive. These ideas have been tested in a number of model systems. They are also significant in real fluids near the critical point, along the coexistence curve, and near the triple point. Also interesting are results for black hole thermodynamics, for which a foundation in terms of an underlying microscopic system is so far absent.   

Numerical method of the quasiclassical theory for mesoscopic superconductors

We propose a numerical method for describing mesoscopic superconductors in terms of the quasiclassical theory of superconductivity. Our method releases us from the problems as to how to determine initial values in a system that does not have a bulk solution. To examine the efficiency of our method, we calculate the local density of states of a circular $d$-wave island sustaining a single vortex. We find that the “vortex shadow” effect strongly depends on the quasiparticle energy in the circular mesoscopic island.   

Discontinuous percolation transition with full step order parameter jump

We demonstrate that there is a class of discontinuous percolation that is characterized by full step jump in order parameter at threshold $p_c=1$. Such a percolation takes place in the infinite dimension if the critical exponent $\tau$, the decay exponent of the cluster number density distribution in critical regime, holds $1<\tau \le 2$. The scaling relations of $\sigma = 2-\tau$ and $\gamma = 1/\sigma$ are derived for the critical exponents $\sigma$ and $\gamma$ associated with the characteristic cluster size and with the susceptibility, respectively. We also show that the cluster number density distribution is compact and can be widened up to $\sim \sqrt{N}$ for system size $N$.   

Three Dimensional Morphology of Lamellae-forming Block Copolymer Thin Films between Two Chemically Nanopatterned Surfaces

Previous work has demonstrated the directed assembly of block copolymers on one chemically patterned surface into desired two dimensional and three dimensional structures. Here, we report on the structures formed by block copolymer thin film equilibrated between two chemically patterned surfaces with orthogonal stripes. The patterned stripes have a width of L$_{0}$/2 and a period of L$_{0}$, where L$_{0}$ is the natural period of the block copolymer. Our experiments and simulations reveal that the block copolymer domains are continuous through the film and the interface between domains resembles the Scherk's first minimal surface. Different from that in the bulk, the interface between the domains is at equilibrium in the presence of the defined boundary conditions, and has a remarkable level of perfection over the patterned areas in centimeter scale. The impact of chemical patterns on block copolymer morphologies and the underlying physics gives insight into the nanofabrication of complex nanostructures with directed self-assembly using two engineered boundary conditions, as opposed to only one.   

Initial condition dependence of the probability density function of the injected power in the Langevin equation

We study the diffusive dynamics of a Brownian particle described by the Langevin's equation with time varying heat bath temperature. Initially (when time $t < 0$) the heat bath temperature is $T_\textrm{init}$ and the particle equilibrates with the heat bath. At time $t=0$, the temperature abruptly changes from $T_\textrm{init}$ to $T$, where their ratio is denoted by $\alpha=T/T_\textrm{init}$. Then the particle follows the Langevin dynamics with the temperature $T$ for $t>0$. Using the path integral method, we compute the probability density function (PDF) of the injection power (injected energy per unit time into the Brownian particle by the random noise, see J. Stat. Phys. 107, 314 (2002)). We find that the PDF or the corresponding large deviation function depends on the initial temperature $T_\textrm{init}$ even in the $t\rightarrow \infty$ limit. In addition, we show that ``phase transition'' of the large deviation function occurs at $\alpha=1/4$.   

Mechanical detection of flux quantums as a candidate for small force standard

Ultra-small force measurement with a micro-cantilever is a novel and powerful tool to probe micro- and nano-scale physical quantities, such as persistent current in mesoscopic metal rings, with unprecedented sensitivity. However, the precision of such small force is often limited by uncertainty of cantilever’s spring constant, partly because of absence of small force standard. In this talk, I will introduce our metrological project for developing a small force standard based on superconducting flux quantum, from its concept to experimental progress. Our experimental results will cover the device fabrication, optical cooling effect, and mechanical detection of magnetic flux quantization and relaxation in a well-defined Nb micro-annulus at a temperature of 4 K.   

Exploring Photocarrier Generation and Recombination in a Smectic Semiconductor \textit{via} Transport Simulations

Photocarrier generation and charge transport in the smectic B phase of the liquid crystalline semiconductor 2-(4'-octylphenyl)-6-dodecyloxynapthalene (8PNPO12) have been investigated by using the time of flight (TOF) technique as a function of light intensity, electric field, and wavelength. The results probe both the low-intensity and space-charge perturbed regimes. The sharply different hole and electron TOF transients are quantitatively analyzed using comprehensive transport simulations to explore exciton dynamics, exciton decay, and bimolecular recombination.   

Charge density waves and superconductivity in a minimal tight-binding model

Charge density waves (CDW) and superconductivity (SC) are observed in a variety of materials such as layered transition-metal dichalcogenides, high-temperature cuprates, organic compounds, and other novel superconductors. The question as to whether CDW cooperate or compete with SC in those materials is under hot debate. In this work, we study possible mechanisms of CDW and its interplay with SC within an extended Hubbard model. In particular, CDW states caused by van Hove singularities as due to the mechanism proposed by Rice and Scott [1] are examined in detail.\\[4pt] [1] T. M. Rice and G. K. Scott, Phys. Rev. Lett. {\bf 35}, 120 (1975).   

Evidence of anisotropic Kondo coupling in nanostructured devices

In spite of recent advances, the theory of electrical conductance through semiconducting nanodevices has fallen short of quantitative agreement with experiment. Consider, in particular, the single-electron transistor, a quantum dot bridging two otherwise independent two-dimensional electron gases. One would expect the universal function $G_{u}(T/T_{K})$ describing the zero-bias conductance for the symmetric spin-degenerate Anderson model as a function of the temperature scaled by the Kondo temperatur $T_{K}$ to match experimental data. In practice, however, attempts to fit measurements with $G_{u}$ have had to rely on \emph{ad hoc} offset adjustments and, even then, obtained only fair agreement. Here, we extend a freshly-derived mapping between the function $G_{u}(T/T_{K})$ and the conductance for the (generally asymmetric) Anderson model to allow for partial screening of the dot moment at high temperatures and show the mapping to fit the zero-bias conductances reported by Grobis et al., Phys.\ Rev.\ Lett.~\textbf{100}, 246601 (2008) within experimental error. While other sources of partial screening cannot be ruled out, our results suggest the Kondo coupling between the dot moment and the electron spins in the adjacent gases to be anisotropic.   

Interactive Learning Solid State with Quantum Mechanical programs

Nowadays Solid State can be learnt interactively with Quantum Mechanical programs. Here we present four systems Na, graphite, diamond and MgB$_{2}$. With these programs their properties, charge density, band structure, density of states can be obtained and with the help of plotting programs their particular characteristics can be studied; type of bond (covalent, ionic, metallic, van der Waals), electrical properties (conductivity, anisotropy). In this form the student can interactively learn to ask questions and obtain answers about the properties of crystalline solids.   

Observation of All-Optical Berezinskii-Kosterlitz-Thouless Transition

The Bereszinskii-Kosterlitz-Thouless (BKT) transition is a two-dimensional dynamic phase transition in which vortex creation competes with entropy production. Each factor is logarithmic in energy, with attempts at long-range order restricted by both geometry and thermal fluctuations. The BKT transition has been observed in a variety of quantum systems, including superfluid films, superconductors, and trapped atomic gases, but it is at root a classical process. Here, we demonstrate a classical BKT transition by observing the 2+1D propagation of an optical beam in a photonic lattice. In this system, there is a one-to-one mapping between the discrete nonlinear Schr\"odinger equation for paraxial propagation and the traditional XY model of condensed matter physics, with thermodynamic averaging replaced by ensemble averaging over initial random phases. We show experimentally that both the number of vortices produced and the universal jump in correlations agree with predictions from mean-field theory. The results give new confirmation of BKT theory, in a purely classical context, and reinforce the use of photonic systems as an experimental testbed for statistical physics.   

Study of the ionic conductivity in Ce$_{1/3}$NbO$_{3}$

Ce$_{1/3}$NbO$_{3}$was synthesized using stoichiometric quantities of CeO$_{2}$ and Nb$_{2}$O$_{5}$ and heated for 48h at 1350$^{o}$C in air. The electric conductivity was measured in the 25$^{o}$C-1000$^{o}$C interval. A small gap of 0.25-0.78eV was found. To study the origin of the transport DFT calculations were carried out; the results show a 0.4eV gap, but since the gaps are not correctly predicted with DFT, a further calculation with a modified Becke-Johnson (mBJ) potential was carried out obtaining a gap of 2eV, but a Ce 4f peak was found at the Fermi energy (E$_{F})$. When an intra-atomic repulsion term was added (LDA+U) the Ce 4f peak moved down and a 2.4eV gap was found. The calculations show that the conductivity does not have electronic origin but ionic. Atomistic calculations rule out that the transport is due to the Ce ions; on the other hand, these calculations agree very well with oxygen ions as charge carriers in this material.   

Sensitive imaging of electromagnetic fields with cold polar molecules

Detection of electromagnetic fields from rf to infrared frequency range is required for numerous applications ranging from test of fundamental symmetries to bioimaging. We propose to use polar paramagnetic molecules, such as SrF, CaH and NH, for sensitive parallel detection of electromagnetic fields. We discuss several methods of detection of both electric and magnetic field components in a wide range of detectable frequencies up to a few THz with high sensitivity and $\mu$m spatial resolution. Our calculations show that, using a gas of SrF molecules, it is possible to achieve sensitivity to ac fields that is two orders of magnitude higher than with ultracold Rb atoms [1]. Various applications are discussed. \\[4pt] [1] P.Bohi, M.F.Riedel, T.W.Hansch, and P.Treutlein, Appl. Phys. Lett. 97, 051101 (2010).   

Resistively Detected NMR and phonon-assisted dynamical nuclear polarization

The resistively detected NMR (RDNMR) is used to detect the nuclear spin polarization and relaxation rates via magnetotransport in the quantum Hall regime. The diagonal term of the hyperfine coupling act on the electrons as an effective magnetic field Bn (Overhauser effect) proportional to the nuclear spin polarization. An oscillatory magnetic field with RF frequency in resonance with the nuclear spin splitting destroys the nuclear spin polarization, and thus the effective magnetic Bn. This induces a measurable change in the longitudinal resistance. Here we show that a finite current dynamically enhances the nuclear spin polarization via two processes: (i) near Landau level crossings a first order hyperfine spin-flip dominates, while (ii) away from crossings a second order phonon-assisted hyperfine spin-flip dominates. Our model show quantitative agreement with recent experiments [Zhang et al., PRL 98, 246802 (2007); Dean et. al., PRB, 80, 153301 (2009); Guo et al., PRB 81, 041306 (2010)]. See also [Ferreira et al., PRL 104, 066803 (2010)].   

Crystal structure and electronic properties of the oxygen deficient Sr$_{3}$Ru$_{2}$O$_{7-y}$ (0$\le $y$\le $0.5) ruthenate

In this work a study of the structural properties of the new non-stoichiometric Ruddlesden-Popper type Sr$_{3}$Ru$_{2}$O$_{7-y}$ compounds is presented. Sr$_{3}$Ru$_{2}$O$_{7-y}$ ($y$ = 0.17, 0.23, 0.28, 0.40 and 0.47) were synthesized by hydrogen reduction of the parent Sr$_{3}$Ru$_{2}$O$_{7}$ ruthenate. Rietveld structure refinements were performed to determine the crystal structure of the reduced compounds. Oxygen content of the samples was studied by redox chemical titration and ESR spectra confirmed the presence of Ru$^{3+}$. Removal of oxygen atoms from the parent compound results in shrinkage of the $c$ and growing of the $a$ lattice parameters, which we related to the Ru$^{4+}$ to Ru$^{3+}$ partial reduction in Sr$_{3}$Ru$_{2}$O$_{7}$. On basis of DFT calculations, with WIEN2k code, we compared the electronic properties of reduced and stoichiometric compounds.   

Dielectrophoretic Tweezers as a Platform for Single Molecular Force Spectroscopy in a Highly Parallel Format

Miniaturization has driven down the cost of tools used in bioanalysis and diagnostics, with single molecules becoming the ultimate detection limit. I will describe how one can exploit mechanical properties of individual biomolecules to determine changes in their state or structure. Our aim is to build a force-spectroscopy-on-a-chip device that can detect and manipulate many (millions) single molecules in parallel. A critical element of this approach is the design of materials properties of molecular handles or probes. By tuning interactions of these probes with electric fields which generate by a simple electrode geometry, we are able to apply piconewton forces to individual DNA molecules and record their response with a single base sensitivity. I will present how we determined the approximate crossover frequency between negative and positive DEP using plain electrodes instead of conventional micro-structures. The technique is attractive not only for conducting single molecule force spectroscopy but also for label-free single cell detection. I will discuss potential applications of this approach to high throughput analyses such as genome sequencing and HIV detection.   

New structural phase transitions in PbMBO$_{4}$ complex oxides: Raman spectroscopy and x-ray diffraction studies

Complex oxides with the mullite crystal structure belong to the most important phase in both traditional and advanced ceramics. Mullites are built of infinite chains of edge-sharing MO$_{6}$ octahedra, bridged by various oxide groups. Interest in metal borates stems from their useful nonlinear optical properties. New complex oxides in the mullite family PbMBO$_{4}$ (M= Fe, Mn, Al) were synthesized and characterized. Using Raman spectroscopy and synchrotron x-ray diffraction at elevated pressure we demonstrate new structural phase transitions.   

Spin-orbit coupling in GaN/AlGaN wurtzite quantum wells

We investigate the spin-orbit coupling for electrons in wurtzite quantum wells with two subbands [1]. By folding down the 8$\times $8 Kane model, accounting for the s-pz orbital mixing [2, 3] absent in zincblende structures, we derive an effective 2$\times $2 Hamiltonian for the conduction electrons. In this derivation we consider the renormalization of the spinor component of the conduction band wave function, which is crucial to properly obtain the corresponding spin-orbit couplings. In addition to the Rashba-type term arising from the bulk inversion asymmetry of the wurtzite lattice, we obtain the usual linear in momentum Rashba term induced by the structural inversion asymmetry of the well and; interestingly, we also find a new Rashba-like contribution. The spin-orbit coupling parameters are obtained via a self-consistent calculation. For completeness, the Dresselhaus term is also included in our calculation. \\[4pt] [1] Rafael S. Calsaverini, Esmerindo Bernardes, J. Carlos Egues, and Daniel Loss, Phys. Rev. B 78, 155313 (2008). \\[0pt] [2] L. C. Lew Yan Voon, M. Willatzen, and M. Cardona, Phys. Rev. B 53, 10703 (1996). \\[0pt] [3] J. Y. Fu and M. W. Wu, J. Appl. Phys 104, 093712 (2008).   

Decoherence Times of Rabi Oscillations in Micro-Plasmas

We study the broadband Rabi oscillations supported by excited states of oxygen atoms in a microplasma. The contrast of characteristic fringe patterns of spectral interference in dynamic Rabi sidebands is determined by decoherence phenomena in a nonequilibrium underdense microplasma channel formed in atmospheric-pressure oxygen gas via interaction with a femtosecond pump pulse. We have established the decoherence rate as a function of the pump pulse intensity, and we have traced the evolution of the decoherence rate as the microplasma evolved toward equilibrium. The rate increases with the pump laser intensity and decreases with the delay with corresponding decoherence times in the range of 750 fs to 3 ps, in good agreement with theory revealing that electron scattering dominates the dynamics for the subnanosecond relaxation processes. The results provide insight into both the behavior of the transient effective two-state systems and the evolution of the characteristics of the laser-generated microplasma.   

Formation of Alkaline Earth Template Layers for Oxide Epitaxy on Semiconductors: Surface Alloying and Self-Organization

The finding that Sr and Ba titanates can be grown epitaxially on Si and Ge (100) surfaces without oxidizing the semiconductor and with atomically abrupt interfaces, has spurred research into exploiting these materials for high-k gate dielectrics and for integrating new functionality into traditional semiconductor devices. To date, all successful oxide eptiaxy on Si and Ge (100) surfaces has required the initial formation of a sub-monolayer of an alkaline earth metal. To understand how this layer promotes oxide epitaxy, we have been using scanning tunneling microscopy complemented by electron diffraction and density functional theory to characterize the formation of the template layer on the atomic scale. The results reveal a complex series of phase transitions as Sr is deposited onto Ge(100). Interestingly, each phase transition is accompanied by drastic changes in the surface morphology that can only be explained by formation of an alloy surface. Through comparison of atomic-resolution STM images with DFT predictions, structural models of two of the surface alloy phases have been deduced. Incorporation of the larger alkaline earth atoms into the surface creates strain that is ultimately relieved by the formation of remarkably well-ordered arrays of stripes and trenches. The alloy formation leads to double-height steps on the surface, resulting in unidirectional trenches and nanowires extending for thousands of Angstroms.   

Photothermal Therapy of Cancer Cells mediated by Blue Hydrogel Nanoparticles

Coomassie Blue dye has been covalently linked into a polyacrylamide nanoparticle matrix, so as to form nontoxic, biologically compatible, biodegradable and cell-specific targetable nanoparticles for photothermal therapy (PTT) of cancer. The nanoparticles were found to be approximately 80-95 nm in diameter, with an absorbance value of 0.52. Using an inexpensive, low intensity LED array light source (590nm, 25mW/cm2), with 20 minute excitation times, at 37$^{\circ}$, PTT induced hyperthermia/thermolysis in HeLa cells, in vitro, resulting in virtually complete cell death when observed 3 hours after exposure. These multifunctional particles have been previously used in cancer delineation, for surgery, and in photoacoustic imaging studies; the addition of the PTT function now enables a multi-pronged medical approach to cancer.   

Entangled Photon Fluorescence with Organic Conjugated Dendrimers

The use of entangled photons for spectroscopy is a novel technique with several potential applications in entangled two-photon excited fluorescence microscopy, quantum imaging and remote sensing. Classical TPA depends quadratically on the input photon flux, whereas, non-classical entangled two-photon absorption (ETPA) has a linear dependence on input flux rate. The total TPA rate measured using an entangled photon source is given by the summation of the ETPA rate and the random TPA rate. This work focuses on the entangled two-photon absorption cross-section and the entangled two-photon fluorescence efficiency of a G1 Dendrimer. From these results, it is shown that the entangled two-photon excited fluorescence of the G1 Dendrimer has a linear dependence at low input photon fluxes. This result has great impact on spectroscopy where the need for small numbers of photons is great, such as microscopy and sensing.