Spring 2025 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223 and Room 2608
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday
Date |
Speaker |
Title and Abstract |
Jan 14 | First Week of Semester | |
Jan 21 | Second Week of Semester after MLK Day | |
Jan 28 |
Student flash talks Host: Sebastien Lepine Room 223 |
1-minute flash talks about student research. |
Feb 4 |
Itamar Kimchi (Georgia Institute of Technology) Host: Yang-Ting Chien Room 223 |
‘Dirty’ Quantum Magnets
Studying quantum entanglement over the past decade has allowed us to make remarkable theoretical progress in understanding correlated many-body quantum systems. However in real materials electrons experience spatially random heterogeneities (“dirt”) whose theoretical treatment, including strong correlations, has been a challenge. I will describe how synthesizing ideas from quantum information theory, statistical mechanics, and quantum field theory gives us new insights into the role of randomness in 2D correlated quantum spin (“qubit”) systems, enabling us to understand a broad variety of experimental observations. I will also describe how these results lead us to conjectures of general UV-to-IR constraints (“Lieb-Schultz-Mattis”) on all possible behaviors of quantum magnets, given a crystal lattice and spin rotation symmetry, even with randomness. |
Feb 11 |
Abhay Nayak Host: Gary Hasting Room 223 |
Unraveling Collective Excitations in Quantum Materials with On-Chip THz Spectroscopy
The advancement of quantum technologies—spanning quantum computing, ultrafast sensing, and next-generation optoelectronics—relies on the discovery and control of exotic electronic phases in quantum materials. Understanding these phases requires not only new material platforms but also advanced experimental techniques capable of probing their fundamental excitations.In this talk, I will explore how engineered two-dimensional van der Waals (vdW) heterostructures provide a versatile platform to realize and manipulate novel electronic states, including fractional topology, unconventional superconductivity, and symmetry-broken phases. A key open question is how collective electronic excitations, such as isospin fluctuations, influence emergent phenomena like superconductivity in bilayer graphene. To address this, I will introduce on-chip terahertz (THz) spectroscopy as a powerful tool for probing low-energy electrodynamics, alongside complementary transport and capacitance measurements. Finally, I will discuss future directions in multi-modal spectroscopy, outlining how next-generation techniques can unlock deeper insights into correlated quantum matter. |
Feb 18 |
Li He Host: Gary Hasting Room 223 |
Topological and nonlinear nanophotonics
Over the past few decades, topology has emerged as a major research direction in condensed matter physics, with the most notable achievement being the discovery of topological insulators. Extending topological concepts to photonic systems has uncovered a wealth of photonic topological states, enabling new ways to control the flow of light. However, many crucial properties unique to photonic systems – such as optical nonlinearity and light-matter interactions – have often been overlooked in prior studies.In this talk, I will present our recent work to address these gaps. First, I will discuss both theoretical and experimental advancements in realizing nonlinear photonic topological insulators in time-modulated photonic crystals, where nontrivial band topology is induced with carefully designed driving fields [1-4]. Next, I will explore how integrating 2D quantum materials with nanophotonics enables strong light-matter coupling, giving rise to topological and nonlinear exciton-polaritons [5,6]. Finally, I will highlight the transformative potential of these phenomena for all-optical information processing, with applications including onchip polaritonic neural networks and quantum polaritonics.Reference:1. Nature Communications 10, 4194 (2019).2. arXiv:2304.09385 (2023).3. Physical Review Letters 126, 113901 (2021).4. Physical Review Letters 129, 063902 (2022).5. Physical Review Letters 130, 043801 (2023).6. arXiv:2411.16635 (2024). |
Feb 25 |
Meera Ramaswamy Host: Gary Hasting Room 223 |
Bridging Scales in Soft and Living Matter: From microscale structure and interaction to emergent macroscale function On the beach, local interactions between sand grains determine whether your castle stands or collapses. Similarly, small changes in the composition of articular cartilage drastically affects its mechanical properties, distinguishing a healthy joint from an arthritic one. Soft and living matter are full of examples where microscale interactions shape macroscale properties. In this talk, I will highlight two examples where I have used experimental tools including microscopy and rheology, and analytic tools rooted in statistical physics to understand and tune the coupling between microscale interactions and emergent macroscale behavior.First, I will discuss the flow behavior of dense suspensions, where interparticle interactions give rise to a dramatic increase in viscosity with increasing stress. Using a scaling collapse of experimental data, I will show that this transition can be described as a crossover scaling between two distinct critical points, leading to a universal scaling function that describes the system behavior. Leveraging these insights, we developed suspension agnostic tools to control the flow of dense suspensions, crucial to the processing of such materials in various industrial applications.Next, I will discuss the growth of multispecies bacterial colonies in three dimensions, mimicking natural environments like the soil or human gut, where the different cell types cooperate or compete for nutrients. By experimentally tracking the growth of two E. coli strains, I will show that even when initially well-mixed, the strains segregate into distinct microcolonies, with the size and shape of each microcolony determined by the initial cell density and colony width. We rationalize these results by considering the interplay between proliferation, competition for space, and competition for nutrients. Our findings shed light on the morphodynamics of mixed microbial communities and provide new insights into proliferating active matter systems in three-dimensional environments.. |
Mar 4 |
Dharmraj Kotekar Patil Host: Gary Hasting Room 223 |
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Mar 11 |
TBD Host: Room 223 |
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Mar 18 | Spring break | |
Mar 25 |
TBD Host: Room 223 |
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Apr 1 |
TBD Host: Room 223 |
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Apr 8 |
TBD Host: Room 223 |
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Apr 15 |
Todd Henry Host: Sebastien Lepine Room 223 |
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Apr 22 |
TBD Host: Room 223 |
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Apr 29 | Final Exam Week Starts / No Colloquium |
Fall 2024 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223 and Room 2608
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday
Date |
Speaker |
Title and Abstract |
Aug 27 | First Week of Semester | |
Sep 3 | Introductory Colloquium | Poster Presentations 1 |
Sep 10 | Introductory Colloquium | Poster Presentations 2 |
Sep 17 |
Maxim Durach (Georgia Southern University) Host: Unil Perera Room 223 |
Theory of Refraction and Electromagnetism in Isotropy-Broken Metamaterials
The familiar tenets of electromagnetism—like the index of refraction being a fixed material property (1.33 for water, 1.5 for glass), rays aligning perpendicularly to wavefronts, and light’s polarization remaining transverse to those rays—must be abandoned when venturing beyond the realm of isotropic media. Today’s electromagnetism grapples with metamaterials exhibiting broken isotropy, resulting in phenomena like direction-dependent indices of refraction, tilted rays relative to wavefronts, and longitudinal polarization linked to bound-charge waves.In this presentation, we will delve into a comprehensive theory encompassing these effects, including the index of refraction operator method, a topological taxonomy of isotropy-broken materials, the connection between broken isotropy and electromagnetism in moving media, and the enigmatic nature of electromagnetic momentum in materials—a challenge considered by some to surpass even Hilbert’s famed mathematical problems in its significance for physics. We will describe how these effects determine the reflection and transmission properties, resonances, and surface electromagnetic waves, in surfaces, layers, and spheres made of chiral, non-reciprocal, anisotropic, and bianisotropic media. |
Sep 24 |
Greg Feiden (University of North Georgia) Host: Idan Ginsburg Room 223 |
Stellar Rotational Evolution: The Key and Barrier to Measuring Stellar Ages Stars are born spinning and continue to do so throughout their life. For low-mass stars like our Sun, their rotation will slow over time as magnetized stellar winds drive angular momentum loss from near the stellar surface. Rotational spindown was observed to be remarkably regular and predictable such that knowing a star’s rotation period could yield an accurate measure of its age—a technique known as gyrochronology. However, results over the last decade reveal that stellar rotational evolution is complicated by two epochs where stars appear to temporarily cease spinning down, casting doubt on gyrochronology’s ability to uniquely assign a star’s age based on its rotation period. In this talk, I will provide an overview of stellar rotational evolution from empirical and theoretical perspectives, highlighting key observational results, theoretical successes, and existing challenges. In particular, I will discuss current progress on understanding the physics governing epochs of anomalous rotational evolution and the future viability of gyrochronology. |
Oct 1 |
LaRonda Rena Brewer (Georgia State University) Host: Sebastien Lepine Room 223 |
Conflict Resolution & Decision-Making Workshop |
Oct 8 | No colloquium | |
Oct 15 |
Spyros Kasapis (NASA Ames Research Center) Host: Viacheslav Sadykov Room 223 |
Using Machine Learning to Predict Space Weather Phenomena Space weather is a branch of space physics that studies the environmental conditions in space caused by solar activity, such as solar flares and geomagnetic storms. Forecasting space weather phenomena is critical in modern times because it helps protect not only essential technologies like satellites, power grids, and communication systems from potential disruptions, but also astronauts from harmful doses of radiation. To mitigate the effects of such phenomena, scientists must understand and predict each step in the sequence leading to space weather disturbances that impact Earth’s environment. To obtain forecasts of the upcoming activity, we develop machine learning models to predict the emergence of large active regions (sunspots) on the solar surface, the primary source of the eruptive activity of the Sun. In some cases, the energy released by these eruptions can accelerate plasma to a very high speed. As a result, the strong flux of highenergy particles that travel through space, so-called Solar Energetic Particles (SEP) events, may impact Earth’s magnetic environment and cause space weather disturbances. We aim to provide machine learning-driven technology that will aid with processing large amounts of historical data from the Solar and Heliospheric Observatory (SoHO) and Solar Dynamics Observatory (SDO) satellites, to forecast SEP events and appearance of active regions that may produce such events. |
Oct 22 |
Nikolai Pogorelov (University of Alabama in Huntsville) Host: Talwinder Singh Room 223 |
Improving Space Weather Forecasts with Data Analysis, Numerical Simulations, and Machine Learning
A new set of open-source software that ensures substantial improvements of Space Weather (SWx) predictions is described. On the one hand, the focus is on the development of data-driven models. On the other hand, each individual component of our software has higher accuracy with a dramatically improved performance. This is done by the application of new computational technologies and enhanced data sources. The development of such software paves way for improved SWx predictions accompanied with an appropriate uncertainty quantification. This makes it possible to forecast hazardous SWx effects on the space-borne and ground-based technological systems, and on human health. Our models involve (1) a new, open-source solar magnetic flux model (OFT), which evolves information to the back side of the Sun and its poles, and updates the model flux with new observations using data assimilation methods; (2) a new potential field solver (POT3D) associated with the Wang-Sheeley-Arge coronal model, and (3) a new adaptive, 4-th order of accuracy solver (HelioCubed) for the Reynolds-averaged MHD equations implemented on mapped multiblock grids (cubed spheres). The software and the results obtained with it are discussed. The results include a solar-cycle long evolution of the ambient solar wind driven by synchronic SDO HMI magnetograms. In addition, we present simulations of a number of coronal mass ejections (CMEs) propagating through the numerically obtained ambient solar wind. Observational data are used to specify the CME properties in the framework of the constant-turn flux-rope method. It is demonstrated that the application of machine learning to modeling CMEs makes it possible to improve SWx predictions by decreasing the time-of-arrival mismatch. The tests show that our software is formally more accurate and performs much faster than its predecessors used for SWx predictions. The application of a specifically designed macro-language makes it possible to use HelioCubed as an example for building other types of software. |
Oct 29 |
Raghav (Rithya) Kunnawalkam Elayavalli (Vanderbilt University) Host: Megan Connors Room 223 |
Back to fundamental QCD – a tale of quarks and gluons!
Collider experiments have proven themselves immensely useful in studying the behavior of fundamental particles such as quarks and gluons. The last few years in particular have seen a push towards an exploration of QCD, the theory of strong interactions, that has hitherto been inaccessible. Innovative experimental techniques allows access to the multi-scale parton evolution and eventually might even shed light on hadronization mechanisms. In the context of heavy ion collisions, jets have been advertised for the past two decades as a useful tool for quarkgluon plasma (QGP) tomography. This quest has had its fair share of roadblocks but I share the community’s roadmap to the next-generation of measurements, with untapped potential to extract of the QGP’s microscopic transport properties and in mapping its space-time evolution. Lastly, I highlight the impact of the upcoming Electron Ion Collider where these novel techniques and experimental precision lead to imaging both the perturbative and non-perturbative QCD regimes, allowing us unprecedented access into color confinement. |
Nov 5 |
Women in Physics and the Undergraduate Research Committee Host: Room 223 |
“Applying to REUs” panel |
Nov 12 |
TBD Host: Room 223 |
FERPA training (postponed) |
Nov 19 |
TBD Host: Room 223 |
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Nov 26 | Thanksgiving Week | |
Dec 3 |
Ramesh Mani (Georgia State University, Physics and Astronomy) Host: Sebastien Lepine Room 223 |
Non-equilibrium excited-state fractionally quantized Hall effects observed via current bias spectroscopy The integer- and the fractional- quantum Hall effects are a quantized version of the Hall effect which is observed in two-dimensional electron systems subjected to low temperatures and strong magnetic fields, in which the Hall resistance Rxy exhibits steps that take on the quantized values. Studies of fractional quantum Hall effects (FQHE) across various two-dimensional electronic systems (2DES) have helped to establish the equilibrium FQHE many-body ground states with fractionally charged excitations and composite particles in condensed matter. Then, the question arises whether an FQHE system driven to non-equilibrium can approach a different stationary state from the known equilibrium FQHE states. To investigate this question, we examine FQHE over filling factors, ν, 2 ≥ ν ≥ 1 under non-equilibrium finite bias conditions realized with a supplementary dc-current bias, IDC, in high mobility GaAs/AlGaAs devices. Here, [1] we show that all observable canonical equilibrium FQHE resistance minima at ∣IDC∣ = 0 undergo bimodal splitting vs. IDC, yielding branch-pairs and diamond shapes in color plots of the diagonal resistance, as canonical FQHE are replaced, with increasing IDC, by excited-state fractionally quantized Hall effects at branch intersections. A tunneling model serves to interpret the results.1) Wijewardena, U.K., Mani, R.G., Kriisa, A. et al. Non-equilibrium excited-state fractionally quantized Hall effects observed via current bias spectroscopy. Commun Phys 7, 267 (2024). https://doi.org/10.1038/s42005-024-01759-7 |
Dec 10 | Final Exam Week Starts / No Colloquium |
Spring 2024 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223 and Room 2608
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday
Date |
Speaker |
Title and Abstract |
Jan 9 | First Week of Semester | |
Jan 16 | Second Week of Semester after MLK Day | |
Jan 18* |
Hao-Yi (Heidi) Wu (Boise State University) Host: Misty Bentz Room 223 |
Probing Cosmic Evolution with Galaxy Clusters
Our understanding of the Universe is at a critical juncture. For decades, the standard model of cosmology based on general relativity, dark matter, and dark energy (ɅCDM) has passed observational tests with flying colors. However, in recent years, the matter density fluctuation amplitude (the S8 parameter) measurements from early-universe probes (cosmic microwave background) and late-universe probes (galaxies and gravitational lensing) have been in notable tension. This S8 tension, if firmly established, would change the standard model of cosmology. In this talk, I will discuss how we use galaxy clusters — the largest gravitationally bound objects in the Universe — to probe cosmic evolution. I will talk about how we use observations across the electromagnetic spectrum to help us understand the astrophysics of clusters, which in turn makes clusters better cosmological probes. I will also discuss how we plan to combine galaxy clusters with other cosmological probes to measure cosmic evolution. |
Jan 23 |
Jinyi Yang (University of Arizona) Host: Misty Bentz Room 223 |
Probing the Earliest Supermassive Black Holes and Their Host Galaxies
Quasars at z~7 hosting highly accreting black holes are unique probes for the early Universe, including the growth of the earliest supermassive black holes (SMBHs), the assembly of their massive host galaxies, and cosmic reionization. I have been leading a distant quasar survey, which yielded the largest sample of luminous quasars at z~6.5-7.6. Pre-JWST, studies using this sample have placed stringent constraints on the intergalactic medium (IGM) evolution and early SMBH growth. The launch of JWST opens up a new era. I will introduce my recent effort to conduct high-resolution observations of a sample of ~30 luminous reionization-era quasars using JWST and ALMA, in synergy with observations in other wavelengths. This dataset allows us to delve into a comprehensive study of the interactions between early SMBHs and their host galaxies at multiple scales and phases, as well as the cosmic reionization. I will present early results, covering quasar physics, AGN feedback, host galaxy stellar emission and gas kinematics, and IGM evolution. These new discoveries mark the beginning of a new era towards understanding the formation of early SMBHs, the assembly of massive host galaxies, and the cosmic reionization. With the upcoming next-generation facilities (e.g., Rubin, Euclid, Roman, and extremely large telescopes), our understanding of these key questions will be significantly advanced in the next decade. |
Jan 30** |
Talwinder Singh (The University of Alabama in Huntsville) Host: Viacheslav Sadykov Room 223 at 3:30pm |
Leveraging Modern Tools and Diverse Data Sources for Improved Space Weather Forecasting
Space weather refers to the varying plasma conditions beyond Earth’s atmosphere, primarily driven by the Sun. Coronal Mass Ejections (CMEs) and solar flares are major sources of disturbances in space weather. These disturbances can adversely affect many of our modern technologies, making the forecasting of CMEs and solar flares crucial. In this talk, I will discuss the current state of the art in CME and solar flare forecasting, along with my research aimed at improving these capabilities. Magnetohydrodynamic (MHD) simulations of solar wind and CMEs, constrained by appropriate observations, represent a promising approach for CME forecasting. Such forecasting involves predicting their arrival time, as well as their plasma and magnetic field characteristics at Earth. The Bz component of a CME’s magnetic field is particularly crucial for determining its geoeffectiveness. Therefore, it’s important that the CME models used in MHD simulations include a flux rope to accurately forecast the CME’s magnetic field. I will explain how we can utilize these models, alongside various remote CME observations and their associated uncertainties, to enhance forecasting accuracy. Additionally, I will discuss how we use machine learning (ML) tools to further improve the prediction of CME arrival times by leveraging data from Heliospheric Imagers. In recent years, solar flare forecasting has advanced significantly, thanks in part to ML-based techniques and big data. In my presentation, I will cover how we are developing various ML methods for solar flare forecasting that show promising performance metrics. I will also highlight the importance of careful data selection for training ML models to achieve improved forecasting accuracy. |
Feb 1* |
Daniel Angles-Alcazar (University of Connecticut) Host: Misty Bentz Room 223 |
Pushing the frontiers of galaxy formation with multi-scale simulations and machine learning
Supermassive black holes (SMBHs) in Active Galactic Nuclei (AGN) play a key role in the formation of galaxies and large-scale structure, but the triggering and impact of AGN feedback across scales and the origin of the observed SMBH–galaxy connection remain major open questions owing to the multi-scale and multi-physics nature of the problem. AGN feedback can also profoundly affect the properties and spatial distribution of baryons on scales that contain a large amount of cosmological information. Current and upcoming cosmological surveys will provide unprecedented data to constrain the fundamental cosmological parameters, but uncertainties in galaxy formation physics remain a major theoretical obstacle to extract information from cosmological experiments. In this talk, I will present new simulation techniques that are pushing the frontiers of galaxy formation modeling towards (1) the smallest scales, developing physically predictive models of SMBH accretion and feedback explicitly at sub-pc resolution in a full cosmological context to interpret a plethora of galaxy and AGN observables, and (2) the largest scales, developing thousands of large-volume simulations exploring a wide range of sub-grid feedback implementations to train robust machine learning algorithms that can maximize the extraction of information from cosmological surveys while marginalizing over uncertainties in galaxy formation physics. I will demonstrate the feasibility of these orthogonal approaches to address fundamental problems and discuss their potential to significantly advance the fields of galaxy evolution and cosmology. |
Feb 6 |
Enrique Lopez Rodriguez (KIPAC, Stanford) Host: Misty Bentz Room 223 |
The effect of magnetic fields on galaxy evolution
Galaxy evolution strongly depends on the physics of the interstellar medium (ISM). The ISM is permeated by magnetic fields (B-fields), in which magnetic energy is in close equipartition with the thermal energy. This physical condition makes the B-fields dynamically important at several stages of galaxy evolution, affecting gas flows in the ISM and driving gas inwards toward the galaxy’s center and outwards toward the circumgalactic medium via galactic outflows. Thus, B-fields are an important, but still overlooked, ingredient to understanding the evolution of galaxies across cosmic time.Far-infrared and sub-mm wavelengths have recently been key to providing a complete picture of extragalactic magnetism by doing what only HAWC+/SOFIA, JCMT/POL-2, and ALMA can do: measuring B-fields in the densest areas of the Universe. Using FIR/Sub-mm and radio polarimetric observations, in combination with the kinematics of the neutral and molecular gas, we have performed a topographic study of B-field in galaxies for the first time. In this talk, I will present the results of SALSA (Survey for extragALactic magnetiSm with SOFIA Legacy Program): the magnetic properties in the multi-phase ISM at 100s pc scales of nearby galaxies (e.g., spirals, starbursts, mergers) observed in the wavelength range of 50-890 um. Then, I’ll present the multi-scale B-field structure in active galactic nuclei, where we found that the most telling and dramatic empirical difference between radio-loud and radio-quiet active galaxies may reside in the presence of strong B-fields helping the transfer of angular momentum and matter from 100s to 10s pc-scales. I will finalize presenting the future projects using SALSA and ALMA to characterize the multi-phase ISM in nearby galaxies and with its synergy with CHARA, the James Webb Space Telescope (JWST), and the next generation of NASA missions. |
Feb 8* |
Liang Zhao (University of Michigan) Host: Viacheslav Sadykov Room 223 at 4pm |
Revolutionizing the Heliophysics Data Analysis with Machine Learning
The Sun is the main energy source for our planet. It generates the solar wind and drives the physical conditions in the region of interplanetary space explored by humans. Since solar wind plasma is inextricably tied to the thermal properties of the inner corona where it is ionized and accelerated, classification of the solar wind by their different coronal origins is crucial to ultimately understanding the acceleration mechanism of the solar wind. Ulysses mission discovered that fast-speed solar wind is originated from low-temperature, low-density coronal holes, however the coronal origin of the slow-speed solar wind is still a puzzle. With the coming era of big data, Machine Learning (ML) and Artificial Intelligence (AI) are changing the existing Heliophysics research in an unprecedented way. In this talk, I will review the pioneer discoveries of the solar wind research and discuss the current challenges. Then I will briefly introduce a few ML/AI methods that can be used in the solar wind data analysis. I will showcase some of our recent results as a demonstration that the application of ML and AI is paving the way for new avenues in Heliophysics research. |
Feb 13 |
Qin Li (New Jersey Institute of Technology) Host: Viacheslav Sadykov Room 223 at 3:30pm |
Harnessing Machine Learning for Understanding Solar Cycle and Solar Flare Activities in Space Weather Research
In this talk, I will delve into the application of cutting-edge machine learning (ML) techniques in the realm of space weather research, particularly focusing on solar cycle variations, solar flare activities and solar data infrastructures. I will begin with an introductory overview of space weather fundamentals, highlighting the influence of solar cycle and solar flare activities on both terrestrial and space-based technologies. The core of the presentation is centered on the integration of ML methodologies into the study of solar physics. I will introduce how ML algorithms, such as Random Forest, deep learning, long term short memory have been employed to analyze vast and complex solar data. This includes ground-based observations like those from Big Bear Solar Observatory (BBSO) to space-borne data from the Solar Dynamics Observatory (SDO). I will discuss how ML approaches significantly improve the precision and efficiency in understanding and predicting solar cycle progressions and solar flare occurrences. In addition, I will discuss the development of predictive models for the long-term solar EUV irradiance.Furthermore, the talk will discuss the challenges faced in this field, such as data quality and availability, Interpretability and Explainability, Integration with Physical Models, Real-Time Processing and Prediction. I will also touch upon the interdisciplinary collaboration between solar physicists, data scientists, and ML experts in advancing these ML approaches in space weather. Finally, the colloquium will conclude with a perspective on future directions in my research. This includes the long-term solar cycle study, i.e., continued study of global-scale surface flows, the reconstruction of long-term Solar EUV irradiance, solar cycle prediction and short-term, solar flare index prediction, and a comparative analysis of magnetic field extrapolation methods, specifically between physics-informed neural networks, optimization techniques, and MHD relaxation.This presentation aims to provide a comprehensive understanding of the current state and future potential of applying ML in the study and prediction of solar cycle variations and solar flare activities, emphasizing their significant roles in enhancing space weather forecasting. |
Feb 20 |
Will Horowitz (University of Cape Town) Host: Yang-Ting Chien Room 223 |
The Physics of a Trillion Degrees
A microsecond after the Big Bang, all of space existed at a trillion degrees, one hundred thousand times hotter than the center of the sun. 13.8 billion years later, massive collaborations of thousands of scientists recreate these conditions of the early universe thousands of times a second in one of the most expensive and complicated science experiments ever attempted. In this talk I provide a general introduction to the physics explored in these Little Bangs, ephemeral fireballs that–during their lifetimes of less than a billionth of a trillionth of a second–are droplets of the hottest, most perfect fluid in the universe. |
Feb 27 |
Student flash talks Host: Sebastien Lepine Room 223 |
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Mar 5 |
Jamie Tayar (University of Florida) Host: Russel White Room 223 |
How well can we estimate stellar ages?
Good estimations of stellar ages are important for a wide range of science cases, from understanding the evolution and habitability of exoplanetary systems to tracking back the cosmic history of our own and other galaxies. These ages, however, are not directly measured, but rather inferred from theoretical models or empirical calibrations using a variety of techniques. I will discuss the current precision and accuracy of isochrone-based, rotation-based, and asteroseismically inferred ages, as well as some of the current challenges of each method. Finally, I will discuss some of the recent and ongoing work in my group to increase the number of stars with well-measured ages, as well as some of the interesting stellar physics puzzles we’ve run into along the way. |
Mar 12 | Spring break | |
Mar 19 |
Mahmoud Asmar (Kennesaw State University) Host: Yang-Ting Chien Room 223 |
Photo-control of Quantum Matter
Recent breakthroughs in the field of condensed matter physics have facilitated the synthesis and exfoliation of quantum materials, which are effectively described by the Dirac equation. These materials, referred to as Dirac materials, introduce novel frameworks for comprehending and implementing electronic, information transfer, and optoelectronic functionalities. Furthermore, there has been a growing interest in manipulating material properties and phases beyond equilibrium states through periodic modulation induced by optical stimuli, a technique termed Floquet engineering. This endeavor has been significantly supported by the advancement of robust and high-intensity radiation sources spanning a wide range of wavelengths. This presentation will delve into the exploration of two-dimensional Dirac materials and their topological characteristics. Additionally, we will assess the potential of Floquet band engineering in manipulating various physical phenomena, including the carrier-mediated magnetic exchange interaction (Ruderman–Kittel–Kasuya–Yosida, or RKKY interaction), the emergence of light-induced vortices in matter, and the photo-induced generation of higher-order topological insulators. |
Mar 26 |
Theja DeSilva (Augusta University) Host: Sumith Doluweera Room 223 |
Slave particle approaches to correlated quantum many-body systems: An application to alkali-doped Fullerides
One of the fascinating aspects of condensed matter physics is the study of how collective and correlated electron behavior give rise to emerging phenomena in materials. In the first half of the colloquium, I will present a broad introduction to emerging electronic phases and then explain how one setup the many-body Hamiltonian to tackle the correlations. In the second half, I will show the application of two popular slave particle approaches to explain recently observed correlated electronic phases in two types of alkali-doped Fullerides. |
Apr 2 |
Haiyan Gao (Brookhaven National Lab), Nelson Speaker Host: Xiaochun He Room 223 |
The Electron-Ion Collider
The U.S. and the broader international Nuclear Physics community have been pursuing the idea of an Electron-Ion Collider (EIC) as the next Quantum Chromodynamics (QCD) frontier for many years. The recently completed 2023 Long Range Plan for Nuclear Science by the Nuclear Science Advisory Committee recommends “the expeditious completion of the EIC as the highest priority for facility construction”. The EIC, a discovery machine, will be built at the Brookhaven National Laboratory in the coming decade. It will enable the definitive study of the role of gluons and quarks in nucleons and nuclei, which are responsible for more than 99% of the visible matter in the universe. The EIC will provide precise images of the gluon/quark structure of the polarized proton, unravel the mysteries of the origin of nucleon mass and spin, and explore the physics of gluons at high density. In this talk, I will discuss the EIC science and the latest status on the EIC. Brookhaven National Laboratory is supported by the U.S. Department of Energy’s Office of Science. |
Apr 9 | No colloquium | |
Apr 16 |
Gail Schaefer (CHARA) Host: Douglas Gies Room 223 |
Imaging Stellar Surfaces with the CHARA Array
The CHARA Array combines the light of six 1-meter telescopes at optical and near-infrared wavelengths with baselines ranging from 34 to 331 meters to achieve milliarcsecond resolution. The Array is used to measure the sizes of stars, image stellar surfaces, detect close binary companions, and resolve the inner structure of circumstellar disks. I will give an overview of the CHARA Array, highlight recent science results, and discuss recent developments to add a seventh mobile telescope to expand the maximum baseline of the Array. |
Apr 23 | Final Exam Week Starts / No Colloquium | |
May 16* |
Tingting Liu (West Virginia University) Host: Misty Bentz Room: PSC 124 (* special venue) |
Cosmic Song and Dance: Probing Supermassive Black Hole Binaries with Electromagnetic and Gravitational-wave Observations
Supermassive black hole binaries (SMBHBs) are thought to form as the result of galaxy mergers. They are expected to produce low-frequency gravitational waves (GWs) that can be detected by pulsar timing arrays (PTAs) and the future Laser Interferometer Space Antenna (LISA). SMBHBs that “light up” as active galactic nuclei (AGN) also emit electromagnetic (EM) radiation and may be observed at optical, X-ray, and other wavelengths. I will highlight some of the observational searches for SMBHBs that I have led, such as mining large time-domain survey datasets to look for the EM imprints of the binary orbital motion and coordinating space- and ground-based observations to test for the theoretically-predicted binary disk structure. I will discuss how these techniques can be applied to upcoming observatories to search for these rare objects and probe accretion physics in dynamic spacetimes. As PTAs and LISA are poised to detect GW signals from individual SMBHBs, they will also open a new discovery space and let us listen to the GW siren songs as the black holes are fated to coalesce. Finally, I will discuss how combining information from EM observations and GWs (i.e., “multi-messenger” observations) can enhance our abilities to detect and characterize these systems – and our experience of the spectacular cosmic song and dance. |
May 28 |
Dieu Duc Nguyen (Centre de Recherche Astrophysique de Lyon) Host: Misty Bentz Room: NSC 218 (* special venue) |
Massive Black Holes and Galaxy Coevolution in the Era of Large Surveys of Integral Field Spectrographs from Ground and Space
It is well-established that supermassive black holes (SMBHs) act as central engines in massive galaxies, influencing mutual evolution with their host galaxies. This relationship is characterized by scaling relations between the SMBH’s mass and large-scale properties of the host galaxy, such as velocity dispersion or stellar mass of the bulge component. However, open questions arise when examining both the lowest- and highest-mass ends of these correlations, as well as their evolution over cosmic time. At the highest-mass end, there is very little observational evidence suggesting that the SMBH mass is roughly one order of magnitude larger than predicted by well-established correlations. This discrepancy hints that the growths of black holes and galaxies may have transitioned from self-regulation to dissipationless dry-mergers of two similarly massive galaxies, as predicted by numerical simulations. On the other hand, evidence of intermediate-mass black holes (IMBHs) remains elusive at the lowest-mass end, despite their importance in constraining the formation mechanisms of black hole seeding within cosmological simulations of the Universe. The existence of IMBHs is expected to produce low-frequency gravitational waves detectable and interpretable by future space-based observatories like the Laser Interferometer Space Antenna (LISA).
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Fall 2023 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223 and Room 2608
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday
Date |
Speaker |
Title and Abstract |
Aug 22 | First Week of Semester | |
Aug 29 | Introductory Colloquium | Poster Presentations 1 |
Sep 5 | Introductory Colloquium | Poster Presentations 2 |
Sep 12 |
Manasvi Lingam (Florida Institute of Technology) Host: Idan Ginsburg Room 223 |
(Sub)Stellar constraints on the habitability of exoplanets
With the rapidly expanding number of exoplanets, understanding the manifold factors that shape (exo)planetary habitability has become increasingly significant. Although habitability is regulated by many planetary parameters, there is growing evidence that the host (sub)stellar object plays a major role in this context. I will outline the research undertaken with my collaborators in the following areas: (1) atmospheric escape mediated by stellar winds and space weather (flares and coronal mass ejections); (2) synthesis of vital prebiotic molecules by UV radiation and/or stellar energetic particles; and (3) potential characteristics of extraterrestrial photosynthesis. Along the way, I will sketch some of the unresolved questions and topics that warrant further study. |
Sep 19 |
Ian Ferguson (Kennesaw State University) Host: Unil Perera Room 223 |
Is Quantum Information (QI@RT) Room Temperature possible?
There is an increasing interest in materials and devices for quantum information (QI) for future computing needs, which are not met using conventional electronics. Quantum computing could enhance the functionalities, storage capabilities, and data manipulation and transmission, for the next generation of devices. Spintronics is an enabling technology to meet the speed, power, and scalability requirements for quantum information. Spin of a material is directly related to magnetic, electrical, and optical properties. However, most materials show conducive properties for spintronics only at cryogenic temperatures, which limits their practical applications. There is a need to investigate spintronic materials for these applications at room temperature (RT).Gallium nitride doped with transition metal or rare earth elements has the potential for controllable spin and charge for spintronics at RT. Gadolinium-doped GaN grown using MOCVD has been shown to have ferromagnetism at RT that is intrinsic and free-carrier mediated from vibrating sample magnetometry and Anomalous Hall effect (AHE) measurements. However, only GaGdN grown using a precursor, which contains oxygen in its organic ligand that is incorporated in the GaGdN exhibited ferromagnetism. Density functional theory calculations show that elements such as oxygen and carbon can introduce localized states near the Fermi level of GaGdN that couple with Gd states and cause p-d hybridization of the p-orbitals of O or C with the d-orbitals of Gd atoms to result in the ferromagnetism. It is necessary to understand the role of O and C in the magnetic properties of GaGdN to be able to control and manipulate its spin. Magnetic, structural, and electrical properties of GaGdN grown with different chemistries and implanted with O or C are investigated in this work in order to gain a better understanding of the origin of ferromagnetism in GaGdN. Understanding of the mechanism for RT ferromagnetism in GaGdN is essential to control the spin and build practical spintronic devices for quantum information applications at room temperature (QI@RT). |
Sep 26 |
Andreas Papaefstathiou (Kennesaw State University) Host: Yang-Ting Chien Room 223 |
Imprints of Electro-Weak Symmetry Breaking at Colliders
With the next generation of collider experiments, we possess the unique opportunity to comprehend some of the most profound scientific questions on the nature of matter and its interactions. In particular, the Higgs field and the electro-weak phase transition link several open mysteries together, intertwining collider measurements with cosmology and astrophysics. In this talk, I will explain the origin of these connections and explore their phenomenological implications. I will focus on the simplest realizations of such phenomena, scalar extensions of the Standard Model, discussing discovery prospects at current and future colliders. |
Oct 3 |
Jianming Wen (Kennesaw State University) Host: Sidong Lei Room 223 |
Harnessing Single Photons and Neutral Atoms: Advancing Quantum Information Science and Technologies through Entanglement Generation
Quantum information science stands at a transformative crossroads, poised to revolutionize diverse fields such as computing, cryptography, communication, networks, metrology, sensing, and imaging. Among various quantum systems, single photons and neutral atoms shine as pivotal catalysts for this quantum revolution. This presentation explores the synergistic convergence of these platforms, with a central focus on pioneering narrowband entangled biphoton sources via spontaneous four-wave mixing (SFWM) in coherent atomic ensembles. Notably, we’ve recently achieved the unique feat of creating a reliable W-class triphoton source through spontaneous six-wave mixing (SSWM) in hot atomic vapor. Our journey commences with foundational quantum concepts, surveys alternative qubit platforms, and dives into conventional biphoton generation methods like spontaneous parametric down-conversion (SPDC) and SFWM in solid materials. We unveil our recent breakthroughs in narrowband bi- and tri-photon generation within coherent atoms, promising long-distance quantum information processing and networking. Single photons, embodying unshakeable quantum properties, serve as versatile information carriers, while neutral atoms offer an ideal setting for nurturing long-lived qubits and quantum memory. We demystify the intricate mechanisms underlying entanglement generation with neutral atoms, shedding light on SFWM and SSWM principles. The talk concludes by showcasing our latest advancements, highlighting our capacity to generate unparalleled coherence and tunability in narrowband entangled photons. These attributes propel scalable quantum networks, connecting quantum processors and enabling secure global information exchange. As we embark on this enlightening journey, we illuminate the pivotal roles of single photons and neutral atoms in advancing quantum information science and technologies, inspiring fresh research avenues toward a quantum-enabled future. |
Oct 10 |
Feryal Ozel (Georgia Institute of Technology) Host: Yang-Ting Chien Room 223 |
We got black hole images. Now what?
The data collected with the Event Horizon Telescope provided the first horizon-scale images of two nearby supermassive black holes. A tremendous amount of theoretical modeling and interpretation, including large simulation libraries and new analysis tools, were necessary to extract physical constraints from these images and perform quantitative tests of General Relativity, plasma physics, and black hole environments. In this talk, I will discuss: 1. the physics behind the simulations and where they succeeded and failed; 2. new directions in plasma astrophysics that are necessary to go beyond the current state-of-the-art; and 3. how the simulation libraries and machine-learning approaches have, in turn, helped us make better black hole images. |
Oct 17 |
Adam Wax (Duke University) Host: Unil Perera Room 223 (Rescheduled to Spring 2024) |
Quantitative phase imaging of nanoscale ultrastructure for analyzing mechanical properties of live cells
The nanoscale ultrastructure of cells can be analyzed using quantitative phase imaging to examine variations in refractive index. By studying cell response to subtle mechanical stimuli, these refractive index variations can be related to viscoelastic properties using parameters such as disorder strength. Comparative studies show that these measures can also be related to shear modulus as determined by atomic force microscopy, a standard tool for mechanobiology. In contrast, the spatial organization of these variations is typically characterized using fractal dimension which is also seen to increase with cancer progression. Our recent work has linked these two measurements using multiscale measurements of optical phase variance to calculate disorder strength and in turn to determine the fractal dimension of the structures. Disorder strength is seen to vary with imaging resolution with fractal dimension revealed in the observed trends over length scale. Studies will be presented which enable distinction of cell phenotype using these two parameters while their combined use presents a new approach for better understanding cellular restructuring. Finally, modulation of these parameters is examined as a means to study early carcinogenic due to heavy metal exposure. |
Oct 24 |
Gongjie Li (Georgia Institute of Technology) Host: Yang-Ting Chien Room 223 |
Dynamical Origin and Habitability of Planets — On the Spin-Axis Variations in Planetary Systems
Thousands of exoplanets have been discovered, and showed properties that are drastically different from that in the solar system. This leads to questions regarding how exoplanetary systems form and evolve into such a variety of states, as well as how inhabitable these systems are. In this talk, we will focus on planetary system spin-axis dynamics, which provides important constraints on the habitability and formation of planetary systems. We will start with stellar spin-orbit misalignment and discuss how it informs us on the formation of close-in planets. Then, we will discuss planetary spin-axis variations and how it influences planet habitability and constraints formation mechanisms. |
Oct 31 |
Marina Kounkel (University of North Florida) Host: Viacheslav Sadykov Room 223 |
Rotational evolution of young stars
In the recent years, with advancements of large surveys such as Gaia and TESS, the ability to measure ages of stars has significantly improved. Current census of stars with know ages exceeds a million stars, and it may soon increase by an order of magnitude. Through measuring rotational periods of variable stars with known ages, we develop an empirical gyrochronology relation of angular momentum evolution that is valid for slowly stars with ages up to 1 Gyr, with the typical precision of ~0.2-0.3 dex. Rapid rotators on the other hand appear to be associated with binary systems with intermediate range of separations, having been sped up following their loss of protoplanetary disks. These data enable detailed characterization of the early evolution of the fundamental properties of star. |
Nov 1 |
KD Leka (NorthWest Research Associates) Host: Viacheslav Sadykov Room 223 |
The Sun as an Experimental Laboratory
Chemistry, biology, physics experiments — all are usually designed to change one thing at a time, judge the results against control samples, and ensure repeatability. However, with observational solar physics, all we have are photons, and historical data (even if that “history” comes from just a few minutes ago). Even Parker Solar Probe can’t directly measure the solar magnetic fields, much less change them. How do you perform experimental science in a remote-sensing laboratory, such as the Sun? The answer lies in “big data”, statistical analysis,
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Nov 14 | No colloquium | |
Nov 21 | Thanksgiving Week | |
Nov 28 |
Megan Connors (Georgia State University, Physics and Astronomy) Host: Sebastien Lepine Room 223 |
Constructing sPHENIX to Study the Quark Gluon Plasma
Colliding heavy ions such as gold at relativistic speeds, recreates a state of matter that existed immediately after the Big Bang and enables us to study the fundamental building blocks of matter known as quarks and gluons which are normally confined within protons and neutrons. This early phase of the universe is known as a quark gluon plasma (QGP) in which quarks and gluons experience asymptotic freedom under extreme temperatures and density. By studying the QGP we further our understanding of Quantum Chromodynamics (QCD), the theory of the nuclear strong force. Of particular interest is the role of the QGP temperature on particle production and interactions, which can be explored by comparing measurements at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). To further facilitate such measurements, a new experiment called sPHENIX specifically designed to measure jets, collimated sprays of particles, and heavy quark observables was built and installed at RHIC. In May 2023, sPHENIX started collecting data from Au+Au collisions at 200 GeV for commissioning the detectors. This talk will highlight the progression of sPHENIX from scintillator tiles at GSU to a fully assembled hadronic calorimeter to first data and the plans forward. |
Dec 5 | Final Exam Week Starts / No Colloquium |
Spring 2023 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223 and Room 2608
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday
Date |
Speaker |
Title and Abstract |
Jan 10 | First Week of Semester | |
Jan 17 | Second Week of Semester after MLK Day | |
Jan 24 |
Shan Wu (Lawrence Berkeley National Lab) Host: Mike Crenshaw Room 2608 |
Magnetic switching resistance materials
Quantum materials are complex systems in which electrons interact strongly and collaboratively. As such, quantum mechanics is dominant in the versatile materials that allow us to explore emergent quantum phenomena and their potential applications in future technologies. Emergent quantum materials embrace material properties that demonstrate the significance of interplay among multiple dimensions in the system. These exotic properties can be harvested into applications for next-generation quantum technologies. Antiferromagnetic (AFM) spintronics is among the newest of quantum technologies, which realize the manipulation of spin-transport in antiferromagnets for memory devices. Recently, the intercalated transition metal dichalcogenide (TMD) antiferromagnet Fe1/3+δNbS2 has shown relevant spintronic features, namely, resistance switching. The original explanation of AFM switching hypothesized that it was driven by a coexisting spin glass phase. Here, I will present our discovery of highly tunable antiferromagnetic orders and discuss how they relate to the observed resistance switching in this material. The rapid change of the magnetic states underlies the sensitive switching behaviors, providing crucial insights on the magnetic ground states that form the basis for understanding the fascinating spintronic behavior. I will also talk about my recent work on this system and open opportunities in the intercalated TMDs as part of the exploration of the spintronic materials. |
Jan 26* |
Kun Wang (Mississippi State University) Host: Mike Crenshaw Room 223 |
Probing Quantum Transport and Energy Conversion at the Molecular Scale
Molecules – the smallest unit of matter – have been playing a pivotal role in today’s materials science, nanotechnology, and quantum science. The capability to manipulate physical and chemical behaviors of single molecules and understand how they respond to external stimuli represents important opportunities for optoelectronics, energy, and quantum applications. In this colloquium, I will talk about my recent studies on developing experimental tools to probe quantum transport in molecular-scale systems and further leveraging them to address challenges in molecular electronics, energy conversion, and nanosensing. First, I will introduce strategies to construct molecular-scale electronic devices, such as diodes and transistors. Second, I will discuss my work on developing new experimental approaches to interrogate thermoelectric energy conversion in molecular junction devices, which points to new opportunities for energy harvesting and refrigeration. Third, I will describe how single molecules can be used as nanoscopic quantum sensors to directly access plasmonic hot carriers and how the experimental approach developed in my work will enable systematic study of plasmon-driven processes in many plasmonic and nanophotonic systems. Finally, I will give an overview for my future research directions. |
Jan 31 |
Jay Mathews (University of Dayton) Host: Mike Crenshaw Room 223 |
At the lasing threshold: Germanium-tin as a gain medium for silicon-based lasers
Silicon is the basis for a multi-billion dollar industry, but its optical properties have limited its use in optoelectronics for infrared (IR) applications. There are a number of applications that could benefit from low-cost Si integrated photonics including photovoltaics, infrared detection and imaging, optical interconnects (OICs), and photonic integrated circuits (PICs). In particular, Si-based OICs and PICs require efficient laser sources, modulators, low loss waveguides, optical switches, and photodetectors, all of which must be integrated into a single Si chip using complementary metal-oxide-semiconductor (CMOS) processing. The biggest gap in technology at the moment is the development of an on-chip light source. One possible solution is to use GeSn alloys as a gain medium for laser devices. These thin films are grown on Si substrates and compatible with standard Si processing techniques, they have band gaps in the infrared, and the band structure of GeSn yields more efficient optical absorption and emission than that in Si. These unique properties have prompted a recent effort to develop optoelectronics from GeSn films, and this research has resulted in a number of prototype photonic devices such as photodetectors that cover all telecommunications wavelengths, infrared light-emitting diodes, and optically-pumped waveguide lasers. However, GeSn waveguide devices have only demonstrated lasing at cryogenic temperatures without complicated strain-inducing structures. In this talk, I will present recent work on the fabrication and characterization of waveguide devices made from GeSn alloys and subjected to optical pumping at room temperature. Based on the results, an emission model was developed to predict the optical emission characteristics based on the material properties, waveguide geometry, and experimental conditions. The model was used to explain the emission data from the GeSn waveguides, and it was compared to other recent GeSn waveguide experiments. I will present details of the modeling, along with some predictions on how room temperature lasing could be achieved in GeSn waveguides. |
Feb 2* |
Yulia Maximenko (National Institute of Standards and Technology) Host: Mike Crenshaw Room 2608 |
Flatland quantum simulation and visualization with atomic resolution
Quantum computing and simulation promise to revolutionize fundamental physics, technology, and quantum chemistry. Simulating quantum systems using analog platforms was first proposed in the 1980s, but recent technological advances have brought this idea to new heights. Trapped atoms and ions, superconducting circuits, and advanced solid-state platforms have achieved an unprecedented level of quantum control and are able to model increasingly complex Hamiltonians. Quantum simulation in 2D solid platforms has proved to be incredibly versatile, while also being compatible with the existing semiconductor technology. In this colloquium, I will showcase the exciting recent developments in the field of 2D quantum simulators, highlighting twisted moiré systems and atomic manipulation. Scanning tunneling microscopy (STM) has proved crucial for the progress of this field. My focus will be on revealing the topological and strongly correlated physics in twisted layered graphene and on the surprising insights gained through the use of STM. Through high-resolution magnetic field scanning tunneling spectroscopy, we have demonstrated the importance of the fine details of quantum geometry in these novel 2D platforms. Specifically, I will report on the discovery of an emergent anomalously large magnetic susceptibility caused by the band topology in twisted double bilayer graphene. |
Feb 7 | No colloquium | |
Feb 14 | No colloquium | |
Feb 21 |
Chen Shi (University of California, Los Angeles) Host: Petrus Martens Room 2608 |
Understanding the solar corona and wind in the epoch of Parker Solar Probe
The outflow of hot plasma from the solar corona, including the more continuous solar wind and the bursty plasma expulsions called Coronal Mass Ejections (CMEs) are the main drivers of space weather. The solar magnetic field, driving the cavity in the interstellar medium in which all planets are embedded, stores and releases a significant amount of energy into the interplanetary space. Understanding the origin and dynamical processes associated with the generation of the solar corona, the acceleration of the solar wind and its ongoing turbulent dynamics are some of the most important tasks of space physics. After decades of exploration fundamental questions concerning the physical processes underlying the origin of the solar corona and solar wind acceleration remain. Two of the most outstanding topics are magnetic reconnection in the solar corona and turbulence in the solar wind. As Parker Solar Probe lowers its orbit into regions close to the Sun never observed directly previously, many novel observations have been made. In this seminar, I will review recent progress on the theory, modeling, and observations of the solar wind. I will discuss opportunities and challenges within the context of current and future missions, including the presently flying, from Parker Solar Probe to Solar Orbiter as well as future in situ exploratory missions such as HelioSwarm. |
Feb 28 |
Luiz Santos (Emory University) Host: Yang-Ting Chien Room 2608 |
Interplay of Interactions and Topology in Electronic Fractals Rapid theoretical and experimental progress in characterizing phases of matter has brought to light a plethora of new topological phases. A remarkable example arises in two-dimensional crystals, where electrons are subject to an external magnetic field. This iconic system supports a rich structure of fractal electronic bands with topological properties that are traditionally linked to the quantum Hall effect, but only recently have been realized in the burgeoning class of moiré crystals. While the non-interacting properties of fractal bands have long been classified, the interplay of interactions and band topology remains a much uncharted territory. In this colloquium I will discuss new quantum behavior that emerges from the interplay of interactions and the self-similar character of fractal bands formed in the presence of large magnetic fluxes. I will present universal results concerning quantum phase transitions and interaction driven electronic orders in fractal bands. Among these are new classes of unconventional superconductors (including topological ones) that fall outside the paradigm of phonon-mediated superconductivity. Fractal electronic bands thus represent rich platforms to explore novel quantum phases of matter. |
Mar 7 |
Lulu Zhao (University of Michigan) Host: Petrus Martens Room 2608 |
Space Radiation Environment
Space Weather is the physical and phenomenological state of natural space environments. One important component of the space weather is the space radiation. Space radiation refers to high-energy ionized particles of different origin present in space are of great concern for aviation, satellites and biological systems. It covers mainly the galactic cosmic ray (GCR) background, solar energetic particle (SEPs) and the Earth’s trapped radiation belts. SEPs are not only a major component of space radiation, but their intensity and energy spectra dramatically change in short periods of time. In fact, the space radiation hazard is one of the major unsolved problems (“tall poles”) hindering space travel beyond low-Earth orbit.SEPs are suggested to be accelerated to high-energy either by magnetic reconnection-driven processes in solar flares or by shocks driven by coronal mass ejections. SEPs can be accelerated up to tens of GeV, and the flux of >10 MeV protons could exceed their background level by several orders of magnitude. Protons of >150 MeV are very difficult to shield, and the sparsity and large variation of the SEP events make them difficult to predict. Many efforts have been made to predict the SEPs using both physics-based approaches and machine learning methods. In this presentation, I will discuss the current status and future visions of the space radiation prediction. |
Mar 9* |
Xiaocan Li (Dartmouth University) Host: Petrus Martens Room 2608 |
Modeling Particle Acceleration and Transport in Solar Flares
Solar flares are among the most explosive and dynamic events in our solar system. These phenomena release massive amounts of energy and can accelerate a large number of particles to very high energies. As these particles can significantly impact our technology and human activities, it is crucial to understand how they are accelerated during solar flares. However, this task is challenging due to the vast and complex nature of solar flares. In recent years, an emerging framework combining theory, numerical modeling, and observations has made significant progress toward understanding particle acceleration during solar flares. In this talk, I will summarize those made by modeling, including kinetic particle-in-cell simulations to study small-scale physics and macroscopic modeling to investigate large-scale processes. By combining these results with observations, we have gained important insights into particle acceleration and transport during solar flares. I will also highlight the challenges in understanding complex physics and interpreting modern high-resolution observations using massive numerical simulations. I will discuss current and future efforts aimed at addressing these challenges. This research area is highly active and exciting, offering numerous opportunities for discovery and impact. |
Mar 14 | Spring break | |
Mar 21 |
Student flash talks Host: Sebastien Lepine Room 2608 |
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Mar 28 |
Ian Ferguson (Kennesaw State University) Host: Unil Perera (Rescheduled to Fall 2023) |
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Apr 4 |
Paul Charbonneau (Université de Montréal), Nelson Speaker Host: Petrus Martens Room 223 |
Avalanches, earthquakes and solar flares
Avalanches, earthquakes and solar flares; beside posing a threat to human societies and infrastuctures, what could these three natural phenomena possibly have in common? They unfold on widely different spatial scales, from hundreds of meters for a snowslope, hundreds of kilometers for a seismic fault, up to tens of thousands kilometer for a solar active region. Moreover, their internal dynamics relies on very different physics: friction between snowflakes, elastic deformation or rock, and dissipation of electrical currents. One key commonality, however, is that all three are natural systems that accumulate energy very slowly, but release it in a strongly intermittent and scale-invariant manner. In this talk I will discuss a physical modelling paradigm whereby such natural complex systems and phenomena emerge from a great many simple dynamical elements interacting locally with one another at scales much smaller than the global scale of the system. Complexity thus emerges from simplicity! In illustrating and explaining these ideas, the emphasis will be placed on solar flares, these being one of the major drivers of space weather. |
Apr 11 |
Sonny Mantry (University of North Georgia) Host: Yang-Ting Chien Room 223 |
Jets as Standard Candles for Particle Physics at Colliders
Jets correspond to highly collimated sprays of energetic particles that emerge from high energy collisions using beams of electrons, protons, or heavier nuclei. Jets are an emergent phenomenon arising from the structure and dynamics of gauge theories such as Quantum Chromodynamics. They serve as beacons for hard interaction processes involving quarks, gluons, and the production of heavy resonances. Understanding the structure, substructure, and dynamics of jets is essential for uncovering hints of new physics, the interactions of elementary particles, and the structure of nucleons and nuclei.In this talk, I will give a pedagogical introduction to the physics of jets, followed by an overview of recent theoretical developments. I will also discuss a few recent applications of jet analyses, including precision extractions of the top quark mass, using jet-based global event shapes as a probe of nuclear structure and dynamics, probing nucleon structure using the electric charge of jets, and exploring the possibility of exotic processes such as charged lepton flavor violation. |
Apr 18 |
Misty Bentz (Georgia State University, Physics and Astronomy) Host: Sebastien Lepine Room 223 |
Comparing Direct Black Hole Mass Measurements in Active Galactic Nuclei
Supermassive black holes appear to be ubiquitous in galaxy nuclei, and several large-scale galaxy properties have been to found to scale with black hole mass, giving rise to the idea that galaxies and their black holes likely co-evolve. There are only a few techniques that can directly constrain the mass of a black hole through its gravitational influence on luminous matter, of which the most commonly applied are reverberation mapping and stellar or gas dynamical modeling. These techniques have been applied to a modest number of black holes, with the vast majority of black hole masses in the literature instead being estimates derived from scaling relationships that are based on these direct results. In the local universe, these scaling relationships are derived from dynamical modeling results, while outside the local universe, reverberation mapping results provide the foundation for different scaling relationships. However, there are only a handful of black holes with masses that have been constrained through multiple techniques because of their disparate technical requirements. When it comes to accreting supermassive black holes, the situation is even worse because they are rare and most are too far away to allow the spatial resolution needed for dynamical modeling. I will describe our ongoing project to directly compare black hole masses from reverberation mapping and stellar dynamical modeling in the nearest Type 1 Seyferts. Both reverberation mapping and stellar dynamical modeling are time- and resource-intensive techniques and the number of galaxies we can study is small, but the results will help uncover potential biases in these direct mass techniques and illuminate any differences in the black hole mass scales that are applied locally versus at cosmological distances. |
Apr 25 | Final Exam Week Starts / No Colloquium |
Fall 2022 Colloquium Schedule
Time: Tuesdays 3 pm to 4 pm. Refreshment starts at 2:45 pm
Venue: 25 Park Place Room 223
Colloquium contact: Yang-Ting Chien ([email protected]) and Viacheslav Sadykov ([email protected])
*Thursday