Colloquium
Fall Colloquia will be held in Room 307 of the Science and Engineering Research Facility (unless slated as virtual in the schedule below) on Mondays at 3:30 PM, EST.
Fall Colloquium Chair, Yuri Kamyshkov (kamyshkov@utk.edu)
Colloquium Fall 2022 Calendar
January 23 |
Department Town Hall Meeting |
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January 30 |
Jérôme Margueron |
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February 6 |
Tao Han |
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February 13 |
Qi Li |
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February 20 |
Steven Prohira |
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February 27 |
OPEN |
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March 6 |
David Radice |
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March 13 |
SPRING BREAK |
NO COLLOQUIUM |
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March 20 |
Ken Burch |
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March 27 |
Andrey Chubukov |
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April 3 |
Joel Moore |
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Alan Tennant |
April 10 |
Bryan Ramson |
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April 17 |
Marcel Franz |
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April 24 |
Michael Peskin |
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May 1 |
Gail McLaughlin |
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May 8 |
HONORS DAY |
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Much of what we know about high-energy components of nuclear structure comes from recent measurement campaigns at Jefferson Lab. Experiments from the 6 GeV era have provided precise results about short-range nucleon-nucleon correlations and their nuclear dependence. Additionally, an intriguing correlation was observed to measurements of modifications of nuclear quark distributions (EMC effect). I will highlight key insights gained from previous measurements (including recent ones) and present future experiments aimed at further illuminating these exotic components of nuclear structure.
Understanding the physics of the high-temperature superconducting cuprates remains a grand challenge for condensed matter physics. The central difficulty here is that the cuprates host a rich set of novel magnetic and charge correlations that can compete/cooperate with superconductivity in ways that are not yet fully understood. In recent years, state-of-the-art nonpertubative numerical calculations for the single-band Hubbard model, a minimal model for the cuprates, have observed similar behavior with several nearly degenerate states closely competing for the ground state. This talk will discuss such numerical studies, including our recent work accessing these physics in the thermodynamic limit, where we find evidence for novel pair-density-wave correlations intertwined with the stripe correlations. I will also discuss how perturbations like the electron-lattice interaction can alter the balance between these competing orders.
While the rise of quantum computers may one day help solve complex problems and deliver information with unhackable security, there is lack of a material platforms for scalable realization of quantum technologies. For instance, the most interesting magnetic property of the celebrated quantum spin liquids (QSLs) is the possibility of quantum mechanical encryption and transport of information, protected against environmental influences. Despite extensive studies on QSLs, they are still far away from applications. First obstacle is simply the shortage of real examples of QSL systems. Second obstacle is that most of the studied QSLs are insulators and electronically inert, which is incompatible with an electrical circuit that relies on moving charge carriers. The grand challenge is to find a way to convert the entanglement information into mobile charge signal by "metallizing" quantum magnets.
In this talk, I will introduce a unique approach by using strategical materials design focusing on geometrically frustrated magnets to address these two obstacles. First, we search for QSL in new spin-1/2 triangular lattice antiferromagnets. The two examples are Na2BaCo(PO4)2 and YbMgGaO4. Second, we explore how to electronically detect the spin sates and spin excitations in newly designed heterostructures based on pyrochlore lattice. The two examples are Dy2Ti2O7/Bi2Ir2O7 and Yb2Ti2O7/Bi2Ir2O7.
I will also introduce the crystal growth techniques used to synthesize these systems since the materials growth is the starting point of materials research and the high quality samples are essential to learn their intrinsic properties.
At energy densities above about 1 GeV/fm^3 QCD predicts a phase transition in nuclear matter to a plasma of quarks and gluons. This matter, called a Quark Gluon Plasma (QGP), has different properties from normal nuclear matter due to its high temperature and density and can be created in high energy nuclear collisions. Measurements at the Relativistic Heavy Ion Collider (RHIC) on Long Island and the Large Hadron Collider (LHC) in Geneva allow studies of nucleus-nucleus collisions over two orders of magnitude in center of mass energy. I will discuss how we can measure the properties of the QGP, even though the liquid produced in these collisions only lives around 10^{-23} seconds, and how we get the most out of those data. I will also discuss incorporation of undergraduates in these studies in a Course-based Undergraduate research experience (CURE). This provides a valuable educational experience for undergraduates while also assisting collaborations and the field with data preservation and comparisons to models. CUREs are a useful tool for increasing research opportunities in the department, increasing diversity in the field, and improving retention in the major.
The first exascale computer, called Frontier, has been delivered to Oak Ridge National Laboratory this past year. This unique scientific instrument is the culmination of more than a decade of concerted effort. I will relate a bit of the history of hybrid-node computing at the Oak Ridge Leadership Computing Facility (OLCF) and how Frontier represents the latest iteration of that approach. Some details of Frontier’s architecture will be discussed, including an overview of the new AMD GPUs that provide the bulk of the computational power for Frontier. Finally, we will take a look at some physics problems that will benefit from the increased capability at exascale, including the last great classical physics problem of turbulence. I will pay particular attention to the effects of turbulent mixing on the explosion mechanism of thermonuclear supernovae, a problem we recently studied on Frontier’s predecessor, Summit.
Discovered in 1986, the cuprate superconductors hold the record for highest superconducting transition temperature (139 K) under ambient pressure. These quasi two-dimensional materials are structurally and electronically very complex, and so is the origin of their spectacular superconducting properties. In this talk, I’ll review some key physical aspects of these materials and show how these insights can be applied successfully to establish two-dimensional superconductivity on the simplest and most ubiquitous electronic materials platform: Silicon. By decorating a p-type Si(111) surface with a dilute monatomic tin layer, we constructed a chiral d-wave superconductor with a critical temperature of up to 9 Kelvin and an upper critical field in excess of 15 Tesla. Chiral d-wave superconductivity is a very rare and exotic state of matter that is characterized by broken time-reversal symmetry and the presence of co-propagating edge modes that are potentially interesting for topological quantum computing. The simplicity and experimental control of simple adsorbate systems may provide a powerful testbed for theoretical models and discovery of elusive phases of quantum matter.
Lattice QCD was invented in 1973-74 by Ken Wilson, who passed away in 2013. This talk will describe the evolution of lattice QCD through the past almost 50 years with particular emphasis on its first years, and on the past two decades, when lattice QCD simulations finally came of age. Thanks to theoretical breakthroughs in the late 1990s and early 2000s, lattice QCD simulations now produce the most accurate theoretical calculations in the history of strong-interaction physics. They play an essential role in high-precision experimental studies of physics within and beyond the Standard Model of Particle Physics. The talk will include a non-technical review of the conceptual ideas behind this revolutionary development in (highly) nonlinear quantum physics, together with a survey of its current impact on theoretical and experimental particle physics, and prospects for the future.
One of the scientific frontiers in quantum magnetism is the discovery and understanding of quantum entangled and topologically ordered states in real bulk materials. At the focal point of the experimental investigation of these quantum spin networks is the identification of fractionalized excitations in transport and spectroscopic measurements. Inelastic neutron scattering has proved a powerful technique to reveal such signatures in a variety of systems ranging from quasi-1D magnets to kagome compounds and more. Recent and on-going developments with neutron scattering instrumentation have allowed the characterization of magnetic excitations in entire volumes of momentum-energy space with high resolution. I this talk, I will discuss how triangular-lattice antiferromagnets, in several different shape and forms, are an ideal testbed for many-body physics. This work was supported by DOE/BES under award DE-SC-0018660 and NSF under award DMR-1750186.
The first detection by the Laser Interferometer Gravitational Observatory (LIGO) of gravitational waves from merging black holes 1.3 billion light years away opened a new window on the Universe. The detection occurred nearly one hundred years after the publication of Einstein’s theory of general relativity (gravity), which predicted the existence of such waves, though Einstein himself doubted their existence and that we would ever be able to detect them. Three primary sources of gravitational waves detectable by LIGO are black hole mergers, neutron star mergers, and core collapse supernovae. Gravitational waves from the first two sources have been detected but not from the last. The last source will be the quintessential multi-messenger source, detectable for a Galactic event in gravitational waves, neutrinos, and photons across the electromagnetic spectrum. What we will learn from such a detection will depend on the sophistication of our core collapse supernova models. The UT–ORNL supernova group is well positioned to provide theoretical input to the gravitational wave astronomy community, in general, and the LIGO Scientific Collaboration, in particular, as we prepare for this watershed event. I will begin with a brief introduction to Einstein’s theory of gravity, without which the concept of a gravitational wave cannot be understood. I will then discuss gravitational waves and past milestone events in which they were detected from each of the first two sources listed above. Results from efforts by the UT–ORNL supernova group to predict core collapse supernova gravitational waveforms will be presented, as well as their implications for detection and culling from a detection information about the supernova central engine. I will then conclude and provide my outlook on the field.
Fermions and bosons are fundamental realizations of quantum statistics, which governs both the symmetry of the wave function under the interchange of particle coordinates and the probability for two particles being close to each other spatially. Anyons in the fractional quantum Hall effect are an example for quantum statistics intermediate between bosons and fermions. Two recent experiments have provided evidence for such exotic anyonic statistics: the collision of anyons in a mesoscopic setup has demonstrated that anyons indeed have a reduced spatial exclusion as compared to fermions, and the symmetry of the quantum mechanical wave function for anyons has been measured directly by braiding anyons around each other in a Fabry-Perot interferometer. I will focus on the theoretical description of anyon collisions, which provides an interesting application of non-equilibrium bosonization.
CERN's Large Hadron Collider has officially embarked on Run 3 after a multi-year shutdown, providing collisions at higher center-of-mass energy and enabling a more efficient delivery of data to the detectors. In this talk I will describe what we hope to learn from Run 3 and future runs of the LHC at the ATLAS Experiment, and the innovations that are helping us make forward progress in our understanding of the fundamental particles of the universe and the forces between them.
The last several years have seen scientists being called upon to offer advice and recommendations with regards to several "crises" that have been impacting both the United States and the world at large. How has the role that science and scientists played been perceived? Science also plays a larger role in the lives of citizens. Examples being in nano-technology, human genomics, modified food crops, and fracking to name several. How should scientists respond to requests for advice and/or solutions? Are there any problems or pitfalls in the process of advising and forming policy?
Experiments with slow neutrons can address interesting scientific questions in nuclear/particle/astrophysics and cosmology. I will present a few examples of issues and experiments from this subfield of scientific activity.
Ineffective use of antibiotics leads to treatment failure and emergence of antibiotic resistance. One major challenge in the field is that our understanding of bacterial response to antibiotics is limited. The research in my lab focuses on quantitatively understanding the effects of antibiotics on bacterial cells and the population. In this talk, I will discuss our on-going research on stochastic population dynamics of bacteria treated with antibiotics. I will present our data that bacterial clearance does not follow a deterministic course but is highly probabilistic. These population fluctuations may be manipulated to facilitate bacterial eradication.
Who Ordered That? I.I. Rabi asked this question when a new particle, the muon, was discovered in 1936. Ever since, this unexpected particle has constantly brought us more surprises, including the pion discovery, parity violation, J/psi discovery, neutrinos and flavor physics etc., opening an avenue in front of us to new physics and new technology. In this talk, I will discuss a new aspect — a high energy muon collider. Due to the recent technological breakthroughs for muon cooling, the muon collider program has regained its momentum. I will present the idea and the current status for a muon collider, and discuss the rich physics potential in exploring the physics beyond the Standard Model, for two representative scenarios: the Higgs factory for the resonant Higgs production and the multi-TeV muon collider at the energy frontier.