Colloquium Schedule

Date

Speaker

Title and Abstract

Shan Wu (Lawrence Berkeley National Lab)

Host: Mike Crenshaw

Room 2608

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.

Kun Wang (Mississippi State University)

Host: Mike Crenshaw

Room 223

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.

Jay Mathews (University of Dayton)

Host: Mike Crenshaw

Room 223

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.

Yulia Maximenko (National Institute of Standards and Technology)

Host: Mike Crenshaw

Room 2608

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.

Chen Shi (University of California, Los Angeles)

Host: Petrus Martens

Room 2608

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.

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.

Lulu Zhao (University of Michigan)

Host: Petrus Martens

Room 2608

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.

Xiaocan Li (Dartmouth University)

Host: Petrus Martens

Room 2608

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.

Student flash talks

Host: Sebastien Lepine

Room 2608

Ian Ferguson (Kennesaw State University)

Host: Unil Perera

(Rescheduled to Fall 2023)

Paul Charbonneau (Université de Montréal), Nelson Speaker

Host: Petrus Martens

Room 223

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.

Sonny Mantry (University of North Georgia)

Host: Yang-Ting Chien

Room 223

Misty Bentz (Georgia State University, Physics and Astronomy)

Host: Sebastien Lepine

Room 223

Date

Speaker

Title and Abstract

Luiz Santos (Emory University)

Host: Yang-Ting Chien

(Rescheduled to Spring 2023)

Fractals are patterns of striking beauty that manifest in a myriad of natural phenomena. Notoriously, fractality emerges in the quantum energy spectrum of electrons in two-dimensional lattices subject to a magnetic field, where the relationship between fractal Hofstadter bands and the quantum Hall effect has revolutionized the understanding of topology in quantum physics. Hofstadter systems have recently experienced a renaissance caused by the advent of moiré superlattices realizing the long-sought regime of large magnetic fluxes in laboratory accessible magnetic fields. Motivated by these developments, I will theoretically discuss novel scenarios for electronic quantum orders that differ from quantum Hall states. In particular, I will show how the self-similar character of fractal bands can give rise to exotic quantum phase transitions and topological superconductivity driven purely from repulsive electronic interactions. These scenarios arise from topological and renormalization group methods newly developed to tackle the challenging yet rich properties of fractal bands, revealing the prospect for exciting new physics in fractal systems.

Ashwin Ashok (Georgia State University, Computer Science)

Host: Xiaochun He

In this talk, I will discuss the interdisciplinary work conducted in my lab, MORSE studio, at the intersection of communication and networking, IoT sensing and robotics, and smart mobile computing. Using these projects as baseline motivation, I will initiate an open forum for discussion on promoting and advancing interdisciplinary research, particularly at the intersection of environment, climate and technology.

Amber Straughn (James Webb Space Telescope)

Host: Misty Bentz

JWST – launched December 25 2021 – is poised to change the way we understand the universe, and we are already making some groundbreaking discoveries in just the first several months of operations.  I will discuss the engineering milestones that made the mission possible, as well as the over-arching scientific themes/goals of the telescope: first galaxies around the time of cosmic reionization, galaxy assembly and evolution, the birth of stars & protoplanetary systems, and study of planets (both within the solar system and exoplanets).  I will also discuss specific scientific programs approved for Cycle 1, as well as early results from the mission.

Host: Yang-Ting Chien

An iconic manuscript preserved at the University of Michigan seems to depict Galileo’s earliest telescopic observations of the moons of Jupiter. Join GSU History professor Nick Wilding as he researches this and other Galileo manuscripts and discovers that things are not always as they seem.

Bernd Surrow (Temple University)

Host: Murad Sarsour

Understanding the properties of nuclear matter and its emergence through the underlying partonic structure and dynamics of quarks and gluons requires a new experimental facility in hadronic physics known as the Electron-Ion Collider (EIC). A US-based facility capable of colliding high-energy polarized electron and ion beams at high luminosity has been envisaged for a long time and articulated as the highest priority for new construction. The EIC will address some of the most profound questions concerning the emergence of nuclear properties by precisely imaging gluons and quarks inside protons and nuclei, such as the distribution of gluons and quarks in space and momentum, their role in building the nucleon spin and the properties of gluons in nuclei at high energies. The EIC facility will be realized at Brookhaven National Laboratory, profiting from the existing Relativistic Heavy-Ion Collider (RHIC) facility, allowing to collide both polarized proton beams and heavy ion beams for more than two decades. High energy polarized p+p collisions at √ s = 200−500 GeV at RHIC provide a unique way to probe the proton spin structure and dynamics using well-established scattering processes. The production of jets and hadrons is the prime focus of gluon polarization studies. The production of W−(+) bosons at √ s = 500 GeV provides an ideal tool to study the spin-flavor structure of the proton. After a summary of final results concerning the spin structure and dynamics of quarks and gluons obtained by the STAR experiment at RHIC, the status and perspectives of a US-based ElC facility will be presented in this colloquium, including highlights of the planned physics program, the current detector design of a new EIC experiment, and anticipated next steps.

Marco Guzzi (Kennesaw State University)

Host: Yang-Ting Chien

The CERN Large Hadron Collider (LHC) is the world’s biggest and most powerful particle accelerator. At the LHC, high-energy beams of protons traveling at approximately the speed of light, collide. I will discuss the physics of the LHC and recent developments in theory and experiments. I will highlight the role of the LHC and future colliders as precision and discovery machines. I will also discuss how our current knowledge of the structure of the proton has an impact on both precision observables and searches for new physics interactions.

Shah Bahauddin (University of Colorado Boulder)

Host: Viacheslav Sadykov

The two primary mechanisms proposed for heating the solar transition region are magnetic reconnection (nanoflares) and wave energy deposition. Our previous work using the Interface Region Imaging Spectrograph showed that the small low-lying loops residing in the transition region are multi-stranded and release bursts of energy via reconnection mediated heating. Additionally, the loop dynamics reveal coexistence of multiple timescales: simulations of the observed UV emission spectra are best reproduced when impulsive heating at the loop apex is combined with intermittent repeated heating at the footpoints on a slower timescale, as expected from magneto-acoustic wave-energy deposition. Thus, signatures of both wave and nanoflares heating may be found at different locations in the same structures. Investigation of individual sources of acoustic emission in a simulated photosphere reveal that the emission is clustered at a spatial scale of several Mm, consistent with the spatial scale of the foot-points of low-lying loops. In this talk, I will discuss (1) how the recent availability of high-resolution, multi-spectral, and polarimetric imaging data from the Daniel K Inouye Solar Telescope would enable us to trace the emission and energy deposition of photospheric waves as they propagate through the chromosphere, and (2) how these waves may drive footpoint motions of the transition region loops and possibly act as the precursor for the magnetic reconnection heating in the low corona.

Andre Bastos (Vanderbilt University)

Host: Mukesh Dhamala

To understand the neural basis of cognition, we must understand how top-down control of bottom-up sensory inputs is achieved. We have marshaled evidence for a canonical cortical control circuit that involves rhythmic interactions between different cortical layers. By performing multiple-area, multi-laminar recordings, we’ve found that local field potential (LFP) power in the gamma band (40-100 Hz) is strongest in superficial layers (layers 2/3), and LFP power in the alpha/beta band (8-30 Hz) is strongest in deep layers (layers 5/6). The gamma-band is strongly linked to bottom-up sensory processing and neuronal spiking carrying stimulus information, while the alpha/beta-band is linked to top-down processing. Deep layer alpha/beta Granger causes that in superficial layers, and is negatively coupled to gamma. These oscillations give rise to separate channels for neuronal communication: feedforward for the gamma-band, and feedback for the alpha/beta band. Attention, working memory, and prediction processing all involve modulation of gamma and alpha/beta synchronization, both within and across areas of the frontal/parietal/visual network. These rhythmic interactions breakdown during anesthesia-induced unconsciousness. Based on these observations, we hypothesize that the interplay between alpha/beta and gamma synchronization is a canonical mechanism to enable cognition and consciousness.

David Ciardi (Caltech/IPAC)

Host: Todd Henry

Over the past two decades, an extraordinary revolution has ensued in our understanding of planetary systems beyond our own, driven largely by the transit missions Kepler and TESS.  Because the transiting missions have relatively poor spatial resolution, high resolution imaging has become standard practice in the vetting of planetary candidates as the community works towards confirmation of a planetary transit as the source of the observed signal.  Our group has become one of the largest providers of such high-resolution imaging, with near-infrared adaptive optics imaging on Keck and Palomar and with optical speckle imaging on Gemini North and South.  While crucial to the confirmation of the planets themselves, the high resolution imaging has enabled us to explore the characteristics of stellar multiplicity and the planets found in those systems.  I will give an overview of our decade-and-half-long program, the role our program plays in the confirmation of planets, and an assessment of the stellar multiplicity and characteristics of the planets found in those systems.

Helen Caines (Yale University), Nelson Speaker

Host: Megan Connors

Quantum Chromodynamics (QCD) predicts that the phase diagram of nuclear matter has a rich structure, including that of a deconfined state of quarks and gluons at extreme temperatures and/or pressure. We have shown that we create such a state, termed the Quark-Gluon Plasma or QGP, in the fireball generated when heavy nuclei are collided at ultra-relativistic velocities. Although we call this medium the Quark Gluon Plasma that’s  a misnomer, it’s actually one of Nature’s most extreme fluids. It has a specific viscosity that is smaller than that of any known substance, including that of superfluid liquid helium, and a vorticity that  surpasses that  of super-cell tornado cores and Jupiter’s Great Red Spot. In addition the Quark Gluon Plasma has quark and gluon degrees of freedom and an initial temperature of a trillion Kelvin, conditions that last existed only a few microseconds after the Big Bang. Understanding the properties of the QGP and locating key features, such as the predicted first order phase transition boundary and the corresponding critical point in the QCD phase diagram, will enhance our knowledge of the universe’s evolution and the structure of all visible matters.

In this talk I will first briefly explain how we have determined these incredible properties of the Quark Gluon Plasma. I will then discuss how we are experimentally  probing different regions of the QCD phase diagram by varying the energy of the colliding beams and the  intriguing hints of a  first order phase transition that these studies have revealed.

Sidong Lei (Georgia State University, Physics and Astronomy)

Host: Sebastien Lepine

2D materials combine multiple unique physical, chemical, and mechanical properties, and thus, continuously inspire new device fabrication strategies and architectures for applications in sensing, energy harvesting, consumer electronics, and many more. In this talk, I will present our recent progress in developing advanced electronic and optoelectronic devices by leveraging this uniqueness. I will introduce a 2D-based adaptive miniature image sensor architecture, which can correct optical aberrations, such as chromatic aberrations and field curvature. This feature can significantly simplify the design of the optical lens for image capturing. Along with the compact device sizes, these image sensors can be drastically downscale the size of cameras to fit in micro-robotics for medical and environmental applications. Besides, I will also discuss the lateral integration techniques for large-scale 2D device fabrication, as well as the vertical coupling and electronic transport behavior across the interfaces on stacked 2D layers. These studies will advance the 3D integration of electronic and optoelectronic devices with more compact volume, faster operation speed, and stronger functions than the current planar integration configurations. Additionally, I will introduce the advanced manufacturing techniques, newly observed mechanical properties of 2D materials, and our home-developed facilities for material processing and characterization in this talk.