Department of Physics & Astronomy "Colloquia and Seminars" Series

Virtual or R-150, Hilbun Hall, Mississippi State University

Fridays @ 3:00 PM

Apr. 28^th, 2023 Dr. Martin Frank, Department of Physics, University of South Alabama

   First Results from NOvA's Magnetic Monopole Search

  Host: Dr. Lamiaa El Fassi

  Abstract:

       The existence of the magnetic monopole has eluded physicists for centuries. The NOvA far detector (FD), used for neutrino oscillation searches, also has the ability to identify slowly moving magnetic monopoles (). With a surface area of 4,100 m$2$ and a location near the earth's surface, the 14 kt FD provides us with the unique opportunity to be sensitive to potential low-mass monopoles unable to penetrate underground experiments. We have designed a novel data-driven triggering scheme that continuously searches the FD's live data for monopole-like patterns. At the offline level, the largest challenge in reconstructing monopoles is to reduce the 148,000 Hz speed-of-light cosmic ray background. In this talk, I will present the first results of the NOvA monopole search for slow monopoles.
       The University of South Alabama hosts a study abroad program to Switzerland and Germany to give students the opportunity to experience particle physics first-hand in Europe. The program commences with a visit to CERN where students get to learn about the particle accelerator and detectors from experts at the forefront of the energy frontier. Another highlight of the program is a visit to Einstein’s 1905 apartment in Bern. In this talk, I will give an overview of the program and how it performed in May 2022 and issue an invitation to interested students from Mississippi State to join us on a future trip.

Past Colloquia/Seminars

Apr. 21^st, 2023 Dr. Padmaja Guggilla, Associate Dean of College of Engineering, Technology, and Physical Sciences for Students Success, Alabama A&M University

   AAMU ADVANCE Initiatives that Inhibit Gender Equity&Promote Inclusion in STEM

  Host: Dr. Dipangkar Dutta

  Abstract:

       Alabama A&M University, one of the largest HBCUs in Alabama received a grant from NSF to increase awareness concerning gender equity and inclusion. AAMU initiated identifying the barriers to success for career advancement and promotion, especially for females and minority groups. This presentation talks about the initiatives taken by AAMU to increase knowledge about rights/laws governing equity, conscious/unconscious biases and equality and provide access to resources for faculty, staff, and administration to better promote an equitable and inclusive environment. The importance of mentoring and the results of the project will be presented.

Apr. 14^th, 2023 Dr. Steve Bromley, Physics Department, Auburn University

   The Surprising Appearance of Atomic Metals in Cometary Atmospheres

  Host: Drs. Donna Pierce and Angelle Tanner

  Abstract:

       Comets are relics of the early solar system – conglomerates of ice and dust that have been preserved at cryogenic temperatures with minimal processing. As comets approach the sun, ices begin to sublimate, producing a large atmosphere of gas and dust that extends hundreds of thousands of kilometers. Excited by sunlight, volatiles such as H2O, CO, and CO2, and their fragments produced by collisions and photochemistry are readily observed from the ultraviolet to the infrared regimes. The presence of metal vapors around comets, however, is historically associated with extreme conditions, such as very close approaches to the sun, or impacts with planets. We located emissions from atoms of nickel and iron in the spectra of comet Hyakutake’s close approach to Earth in 1996. The identifications are confirmed by comparisons to spectral measurements of a nickel-bearing tokamak plasma and a newly developed solar fluorescence model. Using these methods, we recover a non-solar Ni/Fe abundance ratio in the observations of Hyakutake, begging the question: where did the nickel and iron come from? Temperatures in comets at typical distances are insufficient for direct sublimation, and the Ni/Fe abundance suggests a source separate from the bulk composition. I will summarize the fortunate series of events that led us to this work, and motivate organometallics as the possible progenitors of these metal atoms in cometary comae.

Apr. 7^th, 2023 Easter Break: No Colloquium; Enjoy :) and be Safe!

Mar. 31^st, 2023 Dr. Eric Fuchey, Department of Physics & Astronomy, Mississippi State University

   Addressing the Nucleon Spin Puzzle with SpinQuest Experiment

  Host: Dr. Lamiaa El Fassi

  Abstract:

       The Fermilab E1039/SpinQuest experiment aims to measure the transverse single spin asymmetry (TSSA) in several processes such as J/ψ and Drell-Yan dimuon pair production, exploiting the 120 GeV unpolarized proton beam from the Fermilab Main Injector on transversely polarized ammonia and deuterated ammonia targets. Such measurements are anticipated to enhance knowledge about the Sivers function of the nucleon sea. This function represents the correlation between the transverse momentum of quarks and gluons, the building blocks of atomic nuclei, and the spin of the parent nucleon via their orbital angular momentum whose quantification is essential in resolving the "nucleon spin puzzle". In pursuit of the aforementioned asymmetry measurements, our group developed an online reconstruction algorithm harnessing the technical capabilities of graphics processing units (GPU) to provide real-time data monitoring for SpinQuest run periods. Besides a highlight of the SpinQuest plans in elucidating the spin puzzle, the performance metrics of the GPU-based online reconstruction algorithm will be presented along with a description of features and methods employed to reach successful real-time data visualization.

Mar. 24^th, 2023 Dr. Thejesh N. Bandi, Department of Physics & Astronomy, The University of Alabama

   The art and science of atomic clocks and their applications

  Host: Dr. Gombojav ​Ariunbold

  Abstract:

       Precision timing is ubiquitous in our everyday lives – this is a subtle reality. For instance, the workings of telecommunication networks, the stock market, power grid synchronization, navigation – GPS/GNSS, imaging of Blackholes, potential detection of dark matter, etc, all need precision timing in their background, without which it is impossible to operate these technologies. The precision timing, to nanoseconds down to picoseconds or better over a day or longer is only possible with atomic clocks. More so, time as we know has had its definitional binding to atomic clocks since 1967. This shows, everyone on the earth just wants to know what time it is, and is directly or indirectly dependent on atomic clocks. This talk gives an overview of the types of atomic clocks, both ground and space-based clocks that are helpful in enabling the above-mentioned technologies. The presentation will also cover the working principles of the rubidium microwave atomic clocks and the space qualification challenges, with an outlook on the present trends and prospects.

Mar. 17^th, 2023 Spring Break: No Colloquium; Enjoy :) and be Safe!

Mar. 10^th, 2023 Dr. Jennifer Choy, Department of Electrical and Computer Engineering, The University of Wisconsin-Madison

   Photonic engineering of atomic and solid-state quantum emitters for sensing

  Host: Dr. Gombojav ​Ariunbold

  Abstract:

       Quantum sensing relies on the interactions between discrete electronic energy levels of quantum systems and their environment to precisely measure physical quantities such as time, inertial motion, magnetic fields, and temperature. Quantum systems provide an appealing platform for sensing because they can be highly sensitive to small external perturbations, with interactions that are readily described by simple analytical models. In this talk, I will discuss the benefits and challenges of quantum sensors based on thermal and cooled rubidium atoms and solid-state spin defects. While atomic sensors when operated under ideal conditions are inherently stable, their size and complexity pose an implementation challenge to their deployment out of the laboratory. Developments in photonic integration will be critical to enable the practical use of precision atomic sensors, and I will describe our group’s progress toward developing photonic-integrated atomic magnetometers using metasurface-based polarization optics. Meanwhile, analogs of trapped atoms can be found in spin defects in wide-bandgap semiconductors such as diamonds, which are also highly sensitive to local (nanoscale) changes in a magnetic field, temperature, and strain. Solid-state quantum sensors have certain advantages over their atomic counterparts owing to their room-temperature operation without the need for vacuum components and the relative ease of photonic- and RF-component integration. However, near-surface quantum defects exhibit spin decoherence and most of the light emitted is trapped within the bulk crystal. I will summarize our efforts to address these interface challenges, including the modeling of radiative emission of near-surface emitters, the design of metasurface light extractor, and surface termination techniques that improve spin coherence of emitters and enable molecular grafting onto diamond surfaces for chemical sensing.

Mar. 3^rd, 2023 Dr. Shawn D. Pollard, Department of Physics & Materials Science, The University of Memphis

   Spintronics with a twist: Designing chiral magnetism in ultrathin films

  Host: Dr. Ciprian Gal

  Abstract:

       Chirality is a fundamental concept in condensed matter physics. The ability to control the chirality of magnetic structures in thin films has led to the development of new devices governed by control of the local spin structure. To generate this chirality, significant attention in recent years has focused on the Dzyaloshinskii-Moriya interaction (DMI), an antisymmetric exchange interaction that arises from broken inversion symmetry. In particular, broken symmetry at the interface between ferromagnetic materials and materials with strong spin-orbit coupling has allowed for the strength of this interaction, and its balance with other magnetic interactions, to be tuned to give rise to a variety of desired spin structures, chiral domain walls and an object known as the magnetic skyrmion. In this context, the skyrmion refers to small swirling spin textures whose chirality is determined by the sign of DMI. In this talk, I will discuss recent efforts to optimize and control DMI to generate desired magnetic states, and our recent work highlighting the role of compositional variation in thin films capable of hosting chiral domain walls. I will focus on our work with Co/Pd multilayers and complications that arise during attempts to quantify DMI in compositionally non-uniform magnetic thin films.

Feb. 24^th, 2023 Dr. Sampath Gamage, Department of Physics & Astronomy, The University of Georgia

   Quantum Networks Training and Research Alliance in the Southeast (QuaNTRASE)

  Host: Dr. Dipangkar Dutta

  Abstract:

       Quantum Networks Training and Research Alliance in the Southeast (QuaNTRASE)is an interdisciplinary graduate training and research program at the forefront of quantum networks. This NSF-funded initiative is a collaboration between the University of Georgia (UGA), the University of Tennessee Knoxville (UTK), and Oak Ridge National Lab (ORNL). Our faculty researchers come from diverse fields, including Physics & Astronomy, Chemistry, Mathematics, Computer Science, Electrical and Computer Engineering, Industrial & Systems Engineering, Materials Science and Engineering, and Education. QuaNTRASE offers a unique opportunity for students to receive advanced training and research experience in the emerging field of quantum networks. In this talk, I will present our program's background, theme, vision, and goals. Additionally, I will briefly talk about some exciting recent results of our group on hydrogen-doped rare earth nickelates.

Feb. 17^th, 2023 Dr. Dennis Bodewits, Physics Department, Auburn University

   Atomic and Molecular Physics of Comets and Exocomets

  Host: Drs. Donna Pierce and Angelle Tanner

  Abstract:

       Comets are considered primitive leftovers from the era of planet formation. Most comet science questions, therefore, revolve around whether observed properties are primordial, i.e. representative of conditions during the era of planet formation, or whether they are caused by subsequent processing. Comets may also have delivered water and complex molecules to Earth and other planets in our solar system. Finally, the discovery that our solar system is frequently visited by interstellar comets places comet science at the forefront of astrobiology.
      This talk will take you on a tour of key atomic and molecular processes in cometary atmospheres. Like comets in our solar system, it will be difficult if not impossible to directly study the physical and chemical properties of comets around other stars. Instead, we have to infer these properties from the gas surrounding them. Atomic and molecular reactions such as dissociation, ionization, and charge exchange both alter gases surrounding comets. Because many reactions result in the emission of light, they also offer insight into the composition and radiation environment exocomets are exposed to.

          

Feb. 10^th, 2023 Dr. Pankaj K. Jha, Department of Electrical Engineering & Computer Science, Syracuse University

   Small Defect, Big Deal in Quantum Information Science and Technologies

  Host: Dr. Gombojav ​Ariunbold

  Abstract:

       Single photon sources (SPSs) are one of the building blocks for quantum technologies, including optical quantum computing, quantum communications, and sensing and metrology [1]. In the past two decades, various systems have been explored, including heralded SPSs, atoms and atom-like systems as quantum emitters, and highly attenuated lasers. However, both fundamental and technological challenges need to be resolved to achieve a reliable SPS which is scalable and capable of generating single photons on demand with high purity, indistinguishability, and repetition rate.
      In this talk, atomic defects (also known as color centers) in van der Waals crystals of wide-bandgap material such as hexagonal boron nitride (hBN) will be highlighted as a promising candidate for quantum light sources owing to its enticing properties, such as high stability and brightness from cryogenic temperatures to 800 K, convenient integration with flexible substrates, fiber optics, and on-chip photonic devices [2]. In the first part of the talk, I will address two fundamental questions about hBN color centers: (1) Where are these color centers located in any flake? (2) What is the orientation of their dipole moment? I will show our experimental results on the nanometric axial localization (down to ~7 nm) of these color centers with a 3D characterization of their dipole orientation using the phase change material, vanadium dioxide [3]. In the second part of my talk, our recent results on lifetime-limited lines and electrically tunable emission in these color centers [4] will be discussed with potential application in photon-addition quantum technology.

[1] J. L. O’Brien et al., Nat. Photon. 3, 687-695 (2009)
[2] T. T. Tran et al., Nat. Nanotechnol. 11, 37-41 (2016)
[3] P. K. Jha et al., Nanotechnology 33, 015001 (2022)
[4] H. Akbari et al., Nano Lett. 22, 7798 (2022)

Feb. 3^rd, 2023 Dr. Tabetha Boyajian, Department of Physics & Astronomy, Louisiana State University

   Sizing up the Stars

  Host: Dr. Angelle Tanner

  Abstract:

       I will discuss results associated with ongoing surveys to measure diameters and temperatures of main sequence stars with long-baseline optical/infrared interferometry. I will demonstrate how such empirical data are used to construct and calibrate less-direct relationships in order to extend our knowledge to a large number of stars. This analysis includes relations linking color-temperature/radius/luminosity, surface brightness, as well as the global physical properties of temperature-radius-luminosity. The data are also used to identify weaknesses in stellar atmosphere and evolutionary modeling as well as provide empirical constraints to aid in the development of new models. I will discuss how observed discrepancies with models compared to observations have implications for the precise characterization of exoplanets.

Jan. 27^th, 2023 Dr. Jinwu Ye, Department of Physics & Astronomy, Mississippi State University

   Emergent Space-time Meets Emergent Quantum Phenomena

  Host: Dr. Dipangkar Dutta

  Abstract:

       P. W. Anderson said, "More is different ". It says the macroscopic quantum phenomena such as superfluids, superconductors, quantum anti-ferromagnetism, fractional quantum Hall states, etc emerge as the number of interacting particles gets more and more. However, he left the question of how these emergent quanta or topological phenomena change under different inertial frames. In this colloquium, we address this outstanding problem. We propose there is an emergent space-time corresponding to any emergent quantum phenomenon, especially near a quantum/topological phase transition (QPT). We demonstrate this new emergent space-time structure by studying one of the simplest QPTs: Superfluid (SF)-Mott transitions of interacting bosons in a square lattice observed in a frame moving with a constant velocity v relative to the underlying lattice. By both constructing effective actions and performing microscopic calculations on a lattice, we find that the new emergent space-time leads to several new effects in the moving frame such as the change of the ground state (the Mott phase near the QPT may turn into an SF phase, but not the other way around), the emergence of a new class of QPTs, the rising of the Kosterlize-Thouless (KT) transition temperature, the change of the condensation momentum, the sign reverse of the Doppler shift in the excitation spectrum relative to the bare velocity v , etc. In contrast to the Doppler shifts in a relativistic quantum field theory, the Unruh effects in an accelerating observer, and the emergent curved space-time from the Sachdev-Ye-Kitaev model are made. Finally, we show that despite these effects being hard to observe in real materials, but could be detected in cold atoms loaded in an optical lattice.

Jan. 20^th, 2023 Dr. Brad Barlow, Department of Physics & Astronomy, High Point University

   A Search for Stripped Red Giants and Their Significance to Astrophysics

  Host: Dr. Mark Novotny

  Abstract:

       The enigmatic "hot subdwarf" stars represent one of the least-understood stages of stellar evolution. Theory shows they likely formed from red giants that were stripped of their outer hydrogen envelopes due to Roche lobe overflow and common envelope interactions with a nearby companion. Observations seem to support this idea as the large majority of hot subdwarfs are, in fact, in binaries. Many hot subdwarfs show photometric variations, and detailed studies of their light curves help constrain stellar parameters through astroseismological analyses or binary light curve modeling. We have utilized a novel method for identifying new variable hot subdwarf stars using data from the Gaia spacecraft and have been collecting follow-up photometry of these candidate variables using NASA's TESS spacecraft for several years. This work has led to discoveries of systems that might shed further light on how substellar objects affect stellar evolution, whether planets can survive the red giant stage of their host stars, and how many Type 1a supernovae progenitor binaries exist in our Galaxy. In this talk, I will present a general overview of hot subdwarf stars, review their broader significance to astronomy, present the details of our novel variable selection method, and discuss the results of our ongoing photometric survey.

Nov. 25^th, 2022 ***** Happy & Safe Thanksgiving as well as Holiday Seasons; End of the 2022 Fall semester! *****

Nov. 18^th, 2022 Dr. Irina Nesmelova, Department of Physics & Optical Science, The University of North Carolina at Charlotte

   Structural stability and DNA-binding of the primary DNA-recognition subdomain of the Sleeping Beauty transposase

  Host: Dr. Lamiaa El Fassi

  Abstract:

       ​DNA transposons are mobile DNA elements that can move from one DNA molecule to another and thereby deliver genetic information into human chromosomes in order to confer a new function or replace a defective gene. This process requires a transposase enzyme. Sleeping Beauty (SB) transposon is the most widely used DNA transposon in genetic applications and is the only DNA transposon thus far in clinical trials for human gene therapy. A molecular evolution approach has been successfully applied to generate a hyperactive Sleeping Beauty (SB) transposase with approximately 100-fold enhancement in efficiency over the original transposase. While the SB100X transposase variant has been generated, the molecular mechanisms of the hyperactive mutations remain unknown. Notably, the hyperactive mutations are distributed throughout the molecule. Here, we focus on the primary DNA-recognition domain of SB transposase (PAI subdomain) and provide the first experimental evidence of the link between its folding, DNA-binding properties, and enhanced transposition activity. We identify the structure-stabilizing H19Y mutation in the PAI subdomain and define the binding interface between the PAI subdomain and the DNA-core sequence contained in all four transposase binding sites on the transposon DNA. SB transposase containing the H19Y mutation has enhanced DNA-binding activity, which manifests in hyperactivity of transposition. Collectively, our data contribute to our understanding of the role of DNA-binding affinity in SB transposition, and provide important clues for devising novel reagents for genetic engineering.

Nov. 11^th, 2022 Dr. Hui Cao, Department of Applied Physics, Yale University

   Complex Lasers

  Host: Dr. Prabhakar Pradhan

  Abstract:

      A complex laser supports numerous lasing modes and exhibits diverse behaviors, which enable novel applications. I will first introduce random lasers with low spatial coherence for speckle-free full-field imaging. Then, I will discuss a fast and efficient method of switching the spatial coherence of a degenerate cavity laser for bimodal microscopy. Finally, we utilize the spatio-temporal interference of many lasing modes to achieve massively-parallel ultrafast random bit generation with a single laser diode.

Nov. 4^th, 2022$☆$ Dr. Tabetha Boyajian, Department of Physics & Astronomy, Louisiana State University

^☆ Cancelled, to be rescheduled!

Oct. 28^th, 2022 Dr. Ignacio Franco, Department of Chemistry, University of Rochester

   Microscopic Theory, Analysis, and Interpretation of Conductance Histograms in Molecular Junctions

  Host: Dr. Kun Wang

  Abstract:

       ​Molecular junctions have emerged as a powerful tool to investigate chemistry and physics at the single-molecule limit. However, their utility as a platform to develop spectroscopes and construct molecular devices is limited by the broad conductance histogram typically encountered in experiments. Here we advance a microscopic theory of the conductance histogram by merging the theory of force spectroscopy developed in biophysics with molecular conductance. The theory augments the information content that can be extracted from molecular junction experiments and identifies the key physical elements that need to be controlled to enhance the ability of this class of experiments to resolve molecular events.

Oct. 21^st, 2022 Dr. Marlou Slot, Quantum Materials Physicist, National Institute of Standard and Technologies (NIST)

   Atom by atom and layer by layer: Realizing and probing electronic quantum matter

  Host: Dr. Lamiaa El Fassi

  Abstract:

       “Ultimately - in the great future - we can arrange the atoms the way we want; the very atoms, all the way down.” This vision by Feynman has become reality: we can realize electronic quantum simulators at the atomic scale, atom by atom, and layer by layer, opening an experimental avenue to investigate fascinating electronic band structures on demand.
      One route to atomically create and characterize 2D Hamiltonians at will is by controlled patterning of the 2D electron gas at a Cu(111) surface with adsorbed CO molecules in a scanning tunneling microscope. This tunable platform allows for periodic and aperiodic lattices. I will present s- and p-orbital bands in a Lieb and honeycomb lattice and demonstrate that electronic wave functions inherit a dimension of ~1.58 in Sierpinski fractal geometry.
      A second route is given by moiré superlattices of Van der Waals materials such as graphene. Tuning the number of layers, type of material and the twist angle between the stacked layers allows for precise engineering of the superlattice potential, enabling e.g. tunable superconductivity and correlated insulators. I will demonstrate high-resolution local Landau-level spectroscopy in twisted double-bilayer graphene as a quantum ruler for topology and quantum geometry. Deviations from Onsager’s quantization condition reveal an anomalously large energy-dependent magnetic susceptibility - unique for the superlattice periodicities realized in moiré quantum matter.

Oct. 14^th, 2022 Fall Break: No Colloquium; Enjoy :) and be Safe!

Oct. 7^th, 2022 Dr. Laura McCullough, Department of Chemistry and Physics, Wisconsin's Polytechnic University (UW-Stout)

   Standards-based Grading in College Physics

  Host: Dr. Dipangkar Dutta

  Abstract:

       How often have you given a grade to a student where you weren’t sure they really had earned that grade? With a typical points model for grades, and especially with participation or attendance points, a final letter grade does not always reflect how much a student has really learned in a class. An alternative grading model is Standards-Based Grading (SBG) where students earn a grade based solely on how many objectives or standards they have passed. This model can be used for conceptual and numerical problems, as well as lab reports and writing assignments. In this talk, I will share how I use SBG to be confident my students leave my classes knowing physics.
      Standards-based grading (SBG) is an alternative to the standard points model of grading. Students earn a grade based solely on how many objectives or standards they have passed. This model can be used for conceptual and numerical problems, as well as lab reports and writing assignments. In this talk, I will share how I use SBG to be confident my students leave my classes knowing physics.

Sept. 30^th, 2022 Dr. Paul Geuye, Department of Physics & Astronomy, Michigan State University

   Nuclear (or human?) interactions using electromagnetic and rare isotope beams

  Host: Dr. Dipangkar Dutta

  Abstract:

       Scientific discoveries have historically been rooted in the desire for some to take on a quest to tackle the unknown, often with relentless commitments and efforts, and sometimes bold actions that have proven to unravel new pathways. While fundamental forces govern our universe, it is also remarkable that the macroscopic world is a mirror image of the microscopic world in many ways. Using fundamental particles such as the electron or heavier objects like ions as magnifying glasses, nuclear physics have been able to probe the interactions between nucleons inside the nucleus at unprecedented levels. The Facility for Rare Isotope Beams started its highly anticipated experimental nuclear astrophysics program in May 2022 to test our current understanding of a large number of predicted unstable (neutron and proton-rich) nuclei with the possibility to enable new physics beyond the standard model. Impactful scientific results often stemmed from dynamic and multidisciplinary teams of theorists and experimentalists in which both sides listen carefully, process, and understand the information shared. This talk will provide a brief review of the role and successes of nuclear physics experiments and theories as they pertain to my journey in becoming a nuclear physicist, as well as establishing bridges to under-represented groups.

Sept. 23^rd, 2022 Dr. Vinod Menon, Department of Physics, City College of New York

   ​Strong exciton-photon interaction in van der Waals materials

  Host: Dr. Prabhakar Pradhan

  Abstract:

       ​Strong exciton-photon interaction results in the formation of half-light half-matter quasiparticles called exciton-polaritons (EPs) that take on the properties of both its constituents. In this talk, I will first introduce polariton formation in 2D semiconductors [1] followed by a discussion of Rydberg excitons [2] and dipolar excitons [3] to realize highly nonlinear interactions to achieve polariton blockade. Following this, I will discuss the use of strain to control exciton flow and nonlinear response [4]. Finally, I will present some recent results on EPs in correlated van der Waals materials [5] and their potential to realize hybridization between excitons, photons and magnons.

[1] X. Liu et al., Nat. Photonics 9, 30 (2015)
[2] J. Gu et al., Nat. Commun. 12, 2269 (2021)
[3] B. Datta et al., ArXiv2110.13326 (2021)
[4] F. Dirnberger et al., Sci. Adv. 7, 3066 (2021)
[5] F. Dirnberger et al., ArXiv 2203.06129 (2022)

Sept. 16^th, 2022 Dr. Bingqian Xu, Department of Chemistry & Department of Physics, University of Georgia

   Molecular Electronics and Single Molecule Biophysics under Microscope

  Host: Dr. Kun Wang

  Abstract:

       The Single-molecule study, where science and engineering converge, applies the tools and measurement techniques of nanoscale physics and chemistry to generate remarkable new insights into how physical, chemical, and biological systems function. It permits direct observation of molecular behavior that can be obscured by ensemble averaging and enables the study of important problems ranging from the fundamental physics of electronic transport in single-molecule junctions and biophysics of single-molecule interactions, such as the energetics and nonequilibrium transport mechanisms in single-molecule junctions and the energy landscape of biomolecular reactions, associated lifetimes, and free energy, to the study and design of single molecules as devices-molecular wires, rectifiers and transistors, and high‐affinity, anti‐cancer drugs. I will describe, with our exemplary research, the evolution of our pioneered highly integrated SPM-based approaches to simultaneously fabricate, control, modulate, and monitor the electronic and mechanical properties of molecular junction devices and probe the biophysical mechanism of single‐molecule interactions at the single-molecule level.

Sept. 9^th, 2022 Dr. Sean Liddick, Department of Chemistry, Michigan State University

   Exploring the Limits with Rare Isotope Science

  Host: Dr. Ben Crider

  Abstract:

       The Facility for Rare Isotopes Beams (FRIB), located on the campus of Michigan State University, enables the production and study of rare isotopes to better understand the science of the atomic nucleus, how elements are made in the cosmos, the fundamental symmetries of the universe, and how rare isotopes can be put to use in societal applications. FRIB is the newest DOE Office of Science User Facility to come into operation. When FRIB reaches full power the facility is expected to be able to produce most of all possible rare isotopes up to uranium. The science program at FRIB commenced in the spring of 2022. The first two experiments of the FRIB science program focused on the beta decay of short-lived nuclei to explore the structure of the atomic nucleus and the creation of elements in the universe. I will provide an overview of the new facility, how the rare isotopes are made, and examples of the excitement from the first couple of FRIB experiments.

Sept. 2^nd, 2022 Dr. Arash Mafi, Department of Physics & Astronomy, University of New Mexico

   Embracing Disorder in Optics: Anderson Localization Optical Fibers

  Host: Dr. Prabhakar Pradhan

  Abstract:

       Anderson localization has been a subject of fascination and intense research for nearly sixty years. It is highly desirable to harness its curious and exciting properties in practical applications. We have taken a step in this direction by using this phenomenon as the wave-guiding mechanism in optical fibers. In this talk, I will survey recent advances in the fundamental understanding and application of Anderson localization optical fibers. I will discuss recent results on beam multiplexing, image transport, wave-front shaping and sharp focusing, non-local nonlinear behavior, single-photon data packing, and random lasing.

Aug. 26^th, 2022 Dr. Seong-Gon Kim, Department of Physics & Astronomy, Mississippi State University

   Flat-surface-assisted and Self-regulated Oxidation Resistance of Cu(111)

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Oxidation can deteriorate the properties of copper that are critical for its use, particularly in the semiconductor industry and electro-optics applications. This has prompted numerous studies exploring copper oxidation and possible passivation strategies. In situ observations have, for example, shown that oxidation involves stepped surfaces: Cu2O growth occurs on flat surfaces because of Cu adatoms detaching from steps and diffusing across terraces. But even though this mechanism explains why single-crystalline copper is more resistant to oxidation than polycrystalline copper, the fact that flat copper surfaces can be free of oxidation has not been explored further. Here, we report the fabrication of copper thin films that are semi-permanently oxidation resistant because they consist of flat surfaces with only occasional mono-atomic steps. Our first-principles calculations show that mono-atomic step edges are as impervious to oxygen as flat surfaces, and that surface adsorption of $O$ atoms is suppressed once an oxygen fcc surface site coverage of 50% has been reached. These combined effects explain the exceptional oxidation resistance of ultra-flat Cu surfaces.​

          

Aug. 19^th, 2022 Dr. Alibordi Muhammad, Department of Physics & Astronomy, Mississippi State University

   The puzzle of Matter-antimatter Asymmetry: Strange Phase in Beautiful Oscillation

  Host: Dr. Sanghwa Park

  Abstract:

       We live in a matter-dominated universe. According to the principle of conservation of quantum numbers, the matter and antimatter had been produced in an equal (?) amount in the process called Big-Bang. But the present visible universe does not reflect any significant trace of antimatter. In particle physics terminology we call this phenomenon Baryon asymmetry. The question is why the universe had chosen such an asymmetric evolution. Toward answering this fundamental question in 1967 A. Sakharov proposed that Charge (C) conjugation and Parity (P) violation might have played a crucial role in the evolution of baryon asymmetry. In this talk, I will discuss how a CP violating weak phase (Φ_s) can be measured in the laboratory when a neutral strange bottom meson decays to muons and kaons (B_s⁰ → J/ψ Φ → μ⁺ μ^- K⁺K^-). This measurement is performed using the data collected by the Compact Muon Solenoid Experiment based at the Large Hadron Collider. The data is produced in a proton-proton collision at the center of mass energy √s= 13 TeV. I will go through the basic steps of the data analysis for this particular study and at the end, we will discuss what would be the possible impact of such studies in future physics.

Aug. 11^th, 2022^☆ Dr. Mahi R. Singh, Department of Physics & Astronomy, The University of Western Ontario, Canada

   Study of Linear and Nonlinear Plasmonics in Metallic Nanoparticles and Graphene Nanohybrids

  Host: Dr. Kun Wang

  Abstract:

      There is considerable interest in developing nanoscale plasmonic and nanophotonic devices by combining metallic nanoparticles and graphene with quantum emitters (QEs) into hybrid nanostructures. Graphene was invented theoretically by Wallace in 1947 [1] and he found that graphene is a gapless material. Later, Wallace and I found more II-V and II-VI semiconductor gapless materials which have direct band gaps. Most of the research on plasmonics and nanophotonic has focused mainly on noble metals. The problem with the noble metals is that they are hardly tunable and exhibit large Ohmic losses which limit their applicability to plasmonic and optoelectronic devices. On the other hand, graphene plasmons and photonics provide an attractive alternative to noble metal plasmons. The surface plasmon polaritons (SPPs) in graphene can also be tunable via the electrostatic gating technique. Here we investigate the linear and nonlinear optical properties of metallic nanoparticles and graphene nanohybrids in their application to nanotechnology. The photoluminescence (PL), second harmonic generation (SHG) and Kerr nonlinearity have been calculated in the presence of the dipole-dipole interaction (DDI) between QEs. We found that in the weak DDI coupling that there is an enhancement in the PL, SHG and Kerr nonlinearity. On the other hand, in the strong DDI coupling, the peaks in the Kerr coefficient splits from two peaks to four peaks. Physics of the enhancement effect can be used to fabricate nanosensors. On the other hand, the physics of the splitting from one peak (ON) to two or three peaks (OFF) can be used to fabricate all-optical nano switches.

[1] P. R. Wallace, Phys. Rev. 71, 622 (1947)

2022-2023 Committee

email)
Secretary: Susan Galloway (325-2806, srg133@msstate.edu email)

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