January 23 - Sylvain Marsillac, ODU, Department of Electrical and Computer Engineering
Title: "Grain and Grain Boundary Engineering for High Efficiency Cu(In,Ga)Se2 Solar Cells"
Abstract: As world energy demands continue to increase, the need to generate electricity from a broader variety of sources, including renewables, is more important than ever. With costs still 30% higher than those of natural gas, solar energy is a viable contender but more progress is needed to level the playing field with other forms of energy generation. Among the cost drivers that could allow for manufacturing price reductions, high efficiency is critical. In the case of Cu(In,Ga)Se2 solar cells, one of the most prominent polycrystalline thin film solar cells on the market, generating high efficiencies involves engineering both the grains and the grain boundaries, and therefore produces specific requirements. Among those are managing (i) the composition of all elements in the quaternary alloy and the phases in presence, (ii) the deposition process to allow for maximum grain growth and band gap engineering, and (iii) the diffusion of specific impurities for passivation of the grain boundaries. Solutions to these problems, involving synergistic fabrication, characterization and modeling, will be presented and include a multi-step deposition process, controlled gallium content grading for the absorber layer, enhanced in-situ monitoring (by real time spectroscopic ellipsometry), and newly developed alkaline post-deposition treatments. By modifying the deposition process, and engineering both the grain and grain boundary, we will show how the fine-tuning of the Cu(In,Ga)Se2 material properties can lead to enhance solar cell efficiency.
Presentation: OCNPS 200 @ 3:00 pm
Refreshments: OCNPS Atrium @ 2:30 pm
All interested persons are cordially invited to attend.
February 1 - Valerii Vinokour, Argonne National Laboratory
Title: "Confinement and asymptotic freedom with Cooper pairs in superconductors"
Abstract: The standard model of particle physics explains successfully most of the physical realm. Yet, one of its most striking aspects, the confinement mechanism, binding quarks, which are asymptotically free at small scales but confined at large scales, into hadrons is not thoroughly understood. The prevailing model is based on the "dual superconductivity" idea, which is exact in compact QED, where an electric string dual to Abrikosov vortices holds together charges. However, while lattice simulations and the exact solution in the framework of N=2 SUSY Yang Mills theory confirm this theoretical idea, an experimental confirmation, usually sought by advanced accelerator measurements, remain scarce. We develop a topological gauge theory of superinsulators in disordered materials and demonstrate that the superinsulating state, dual to superconductivity, manifestly realizes the confinement phenomenon and constitutes hence a perfect laboratory to explore its experimental implications. We identify the mechanism of superinsulation, leading to an infinite resistance at finite temperatures, as Polyakov's magnetic monopole condensation resulting in linear confinement of Cooper pairs 8 and displaying asymptotic freedom in a form of the quantum metal on the samples smaller than the string scale. Accordingly, the superconductor-insulator transition (SIT) epitomizes an experimental realization of the field-theoretical S-duality. We derive the deconfinement temperature and reveal an intermediate deconfined phase, the topological insulator where neither magnetic nor electric excitations condense. We show that superinsulators may appear in two flavors, normal- and strong ones. Strong superinsulators harbor fundamental "fermionic" strings 22. Our findings generalize the concept of a superinsulator to 3D systems and open the route to desktop experiments revealing and elucidating observable consequences of confinement.
Presentation: OCNPS 200 @ 3:00 pm
Refreshments: OCNPS Atrium @ 2:30 pm
All interested persons are cordially invited to attend.
February 15 - Pradeep Kumar, University of Wisconsin-Madison
Title: "Origin and Reduction of 1/f Magnetic Flux Noise in
Superconducting Quantum Circuits"
Abstract: Low frequency 1/f magnetic flux noise is a dominant contributor to dephasing in superconducting quantum circuits. Recent work indicates that the noise is from a high density of unpaired magnetic defect states on the surfaces of the superconducting thin films. I will demonstrate that adsorbed molecular O2 is the dominant contributor to magnetism in superconducting thin films. I will show that this magnetism can be reduced by appropriate surface treatment or improvement in the sample vacuum environment. Effects of surface treatments on qubit dephasing will be discussed. These advances open the door to the realization of superconducting qubits with improved dephasing times.
Presentation: OCNPS 200 @ 12:30 pm
Refreshments: OCNPS Atrium @ 12:15 pm
All interested persons are cordially invited to attend.
February 20 - Zhu Diao, School of Physics Trinity College Dublin
Title: "Membrane-based AC Nanocalorimetry for Characterizing Superconductors in Sub-microgram Amounts"
Abstract: High quality heat capacity measurements play an important role in modern condensed matter physics research. However, measurements involving samples of sub-microgram in mass or energies in the sub-nanojoule scale are extremely difficult to perform. Conventional calorimeters are marked by the large heat capacity contribution of the calorimeter cell (addenda), thus, not suitable for such applications. We developed a SiNx-membrane-based differential AC nanocalorimetry platform, which enjoys drastically reduced addenda as well as excellent isolation between the sample and the environment. It is capable of measuring sub-microgram samples with both ultrahigh resolution and outstanding accuracy.
In the first part of the talk, I will describe the design and operation principles of our AC nanocalorimeter. The focus will be on our unique fixed-phase, variable frequency measurement scheme, which allows accurate determination of sample heat capacity at any given temperature. In the second part of the talk, I will discuss how our nanocalorimetry platform can be utilized to characterize two types of novel superconducting materials, namely, the metastable beta phase of gallium and the phosphorous-substituted Ba-122 compound (one of the recently discovered iron-based superconductors). Our heat capacity data provide a wealth of information on the superconducting states of both materials, allowing insight into their electronic structures and pairing mechanisms.
Presentation: OCNPS 200 @ 12:30 pm
Refreshments: OCNPS Atrium @ 12:15 pm
All interested persons are cordially invited to attend.
February 22 - Nirmal J. Ghimire, Argonne National Laboratory
Title: "Materials Approach to Emergent Phenomena in Condensed Matter"
Abstract: Emergent phenomena in condensed matter physics, which result from cooperative effects and thus cannot be predicted from the properties of individual electrons, extend beyond the realm of strongly correlated electron systems. The recent examples include topological materials such as Dirac and Weyl semimetals. In this talk, I will present a snapshot of my broader strategy in the search for the emergent phenomena in such topological materials. I will first start by reporting my recent studies on Weyl semimetal NbAs. A Weyl semimetal is a conductor whose low-energy bulk excitations are Weyl fermions. I will present the experimental signature of an emergent behavior of Weyl fermions in NbAs observed in magnetotransport measurements. In the second part, I will talk about my new approach of searching for emergent properties by combining topological features and magnetic textures in a single material. In an attempt to follow this direction, I have found an unusual anomalous Hall effect in a noncentrosymmetric antiferromagnet CoNb3S6, which we attribute to a novel interplay between the magnetic and electronic degrees of freedom.
Presentation: OCNPS 200 @ 12:30 pm
Refreshments: OCNPS Atrium @ 12:15 pm
All interested persons are cordially invited to attend.
February 27 - Siyuan Dai, University of Texas at Austin
Title: "Hyperbolic phonon polaritons in hexagonal boron nitride"
Abstract: Hyperbolic systems where principal components of the permittivity tensor have opposite signs enable a series of advances in nanophotonics including negative refraction, subdiffractional imaging and super-Planckian thermal emission. While hyperbolicity was previously achieved with metamaterials by artificial fabrication, we discovered natural hyperbolicity in hexagonal boron nitride (hBN) due to anisotropic phonons in the mid-infrared. The hyperbolicity in phononic hBN is immune to electronic losses as directly revealed in nano-imaging of highly confined and low-loss hyperbolic phonon polariton waves. These virtues allow subdiffractional focusing and imaging via hBN slab with a record high resolution. By stacking hBN and graphene in the form of van der Waals heterostructure, we have demonstrated the dynamic tuning of hyperbolic response though plasmon-phonon hybridization. Furthermore, we have accomplished a high degree manipulation and steering of polaritonic waves as well as imaging concealed inner structure in a fashion of polariton tomography.
Biosketch: Siyuan Dai received his B.S. degree from University of Science and Technology of China in 2011 and Ph.D. from University of California, San Diego in 2017. He is now a Postdoc Research Fellow at the University of Texas at Austin. His current research focuses on nanophotonics & light-matter interactions in low dimensional materials.
Presentation: OCNPS 200 @ 12:30 pm
Refreshments: OCNPS Atrium @ 12:15 pm
All interested persons are cordially invited to attend.
March 1 - Guangxin Ni, Columbia University in the City of New York
Title: "Nano-plasmonics in graphene/hexagonal boron nitride heterostructures"
Abstract: The term 'plasmonics' often carries an applied connotation owing to its remarkable successes in controlling and manipulating light at the nano-meter length scales. Graphene is proposed as one of the most promising candidates for novel plasmonics, owning to its versatile tunability, broadband frequency capability and ultrafast operation speed. In this talk, we present infrared nano-optics studies of graphene encapsulated with hexagonal boron nitride (hBN) to forming van der Waals hererostructures. We have uncovered a rich variety of plasmonics effects that may enable functionalities not attainable through bulk metal-based plasmonics. Through direct nano-imaging of plasmonic standing waves we were able to quantify the fundamental losses in graphene. By examining the sub picosecond dynamics of plasmons in a unique set of pump-probe spectroscopy apparatus we were able to switch on plasmon on demand [Nature Photonics 10, 244 (2016)]. In addition, we performed nano-imaging of graphene/hBN assembling with the presence of a periodic moiré superlattice structures, which yielding rich insights into the electronic phenomena of the hosting material [Nature Materials 14, 1217 (2015)]. Furthermore, we will also discuss the able to map and characterize plasmonic domain boundaries in graphene that is created by a tunable potential barrier through nearby one-dimensional line-like perturbations [Physics Review Letters 117, 086801 (2016)].
Presentation: OCNPS 200 @ 12:30 pm
Refreshments: OCNPS Atrium @ 12:15 pm
All interested persons are cordially invited to attend.
March 27 - Sergey Kulagin, Institute for Nuclear Research of the Russian Academy of Sciences, Moscow
Title: "The EMC effect in light and heavy nuclei"
Abstract: The deep-inelastic scattering (DIS) and the Drell-Yan (DY) experiments with nuclei demonstrated significant nuclear effects on the parton level. These observations rule out the naive picture of the nucleus as a system of quasi-free nucleons and indicate that the nuclear environment plays an important role even at energies and momenta much higher than those involved in typical nuclear ground state processes. The understanding of nuclear effects at the parton level is relevant for interpretation of the results of high-energy experiments in different fields including DIS with charged leptons and neutrinos, DY process, heavy-ion collisions. In this talk I review the data on the nuclear EMC effect and discuss a microscopic model of nuclear structure functions (parton distributions), which takes into account a number of physics mechanisms responsible for nuclear corrections.
Presentation: OCNPS 200 @ 3:00 pm
Refreshments: OCNPS Atrium @ 2:30 pm
All interested persons are cordially invited to attend.
April 10 - Dr. Oscar G de Lucio, Instituto de Física, Universidad Nacional Autónoma de México (CANCELLED)
Title: "TBA"
Abstract:
Presentation: OCNPS 200 @ 3:00 pm
Refreshments: OCNPS Atrium @ 2:30 pm
All interested persons are cordially invited to attend.
April 17 - Senior Thesis Presentations
Senior Thesis Presenters
Philip Stuckey
Advisor: Professor Hyde
Kelly Sanderson - Optimizing an analysis of the neutral hydrogen content of galaxy groups in the Illustris-1 simulation
Advisor: Professor Terzic
Matthew Splitstone
Advisor: Professor Kuhn
Andrew Dotson
Advisor: Professor Whelan
Session 2: 3:00 - 5:00pm
Ken Workman - Construction of an Apparatus for Studying Injection Locking of a Diode Laser
Advisor: Professor Sukenik
Forrest Miller - MATLAB Code for Spectrometer Calibration for Plasma Spectroscopy Applications
Advisor: Professor Popovic
April Savage - Investigation of Polarization Effects in LiDAR Backscattering
Advisor: Professor Sukenik
Alexander Maddock - Exploring Laser Saturated Absorption Spectroscopy of Krypton in a Radio-Frequency Discharge
Advisor: Professor Sukenik
Amelia Verges - US Military Nuclear Weapons: Make-up, Detection, and Destruction
Advisor: Professor Bueltmann
Trenton Hagerman - Semi-analytical methods for inverse Compton scattering
Advisor: Professor Terzic
Jason Morgan
Advisor: Professor Kuhn
Presentations: OCNPS 142/144 (Scale-Up)
Lunch and Refreshments will be served: Scale-Up
All interested persons are cordially invited to attend.