Physics and Astronomy Colloquia

# Department of Physics & Astronomy "Colloquia and Seminars" Series

## Fridays @ 3:00 PM

NB: Unless noted otherwise, Physics Colloquia/Seminars are held as mentioned above.

• Nov. 25th, 2022 ***** Happy & Safe Thanksgiving as well as Holiday Seasons! *****

*** End of the 2022 Fall semester; Will reconvene on January 2023! ***

• Nov. 18th, 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.

• ### Past Colloquia/Seminars

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

•    Complex Lasers

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

• Cancelled, to be rescheduled!

• Oct. 28th, 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. 21st, 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. 14th, 2022 Fall Break: No Colloquium; Enjoy :) and be Safe!

• Oct. 7th, 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. 30th, 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. 23rd, 2022 Dr. Vinod Menon, Department of Physics, City College of New York

•    ​Strong exciton-photon interaction in van der Waals materials

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. 16th, 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. 9th, 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. 2nd, 2022 Dr. Arash Mafi, Department of Physics & Astronomy, University of New Mexico

•    Embracing Disorder in Optics: Anderson Localization Optical Fibers

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. 26th, 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.​

We also introduce colossal oxidation resistance (COR), which not only provides permanent protection against room-temperature oxidation of oxidizable metals but also is robust even against high-temperature oxidation. Our first-principles calculations show that the COR originates from complete blocking of the oxygen entry path into the metal by oxygen atoms themselves and the reconstitution of the metal surface forms an atomically thin barrier impenetrable to oxygen at high temperature. This reliable approach to creating COR will open new directions for research fields and industries hesitating to use oxidizable metals.

• Aug. 19th, 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 (Φs) can be measured in the laboratory when a neutral strange bottom meson decays to muons and kaons (Bs0 → 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. 11th, 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)

Special pre-semester colloquium held on a different date and time, Thursday @ 1:30 PM.

### 2022-2023 Committee

Gombojav O. Ariunbold (325-2927, ag2372@msstate.edu email)
Lamiaa El Fassi (Chair) (325-0627, le334@msstate.edu email)
Dipangkar Dutta (325-3105, d.dutta@msstate.edu email)
Angelle Tanner (325-4112, at876@msstate.edu email) )
Kun Wang (325-2806, kw2504@msstate.edu email)
Jinwu Ye (Spring 2023 ONLY) (325-2926, jy306@msstate.edu email)
Secretary: Susan Galloway (325-2806, srg133@msstate.edu email)

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