Prof. Jeanie Lau

Department of Physics

The Ohio State University

Host: Chunli Huang

Title: Flat Bands and Quantum Geometry in Flatlands

Abstract: In a flat band, the electronic interactions dominate, leading to emergent correlated phases such as superconductivity and charge density waves. The advent of flatlands, i.e. two-dimensional (2D) materials provide us with unprecedented opportunities to design and engineer flat bands via stacking, magnetic fields, and twisting. For flat bands in flatlands, quantum geometric contributions become important. To illustrate this, I will focus on superconductivity in twisted bilayer graphene, in which the slow Fermi velocity and the small charge density appear to invalidate conventional BCS equations and present a paradox. The paradox is resolved by our experimental demonstration that the superfluid stiffness is dominated by the quantum geometric contribution. We also find that the band velocity in this Dirac superconductor constitutes a new limiting mechanism for the critical current, analogous to a relativistic superfluid. Finally, I will also present on flat bands in suspended few-layer graphene, where gate tunable magnetism is observed. 

Nathaniel Craig

Associate Professor

Department of Physics

University of California, Santa Barbara

Host: Susan Gardner

Title: The “Who Ordered That” Collider

Abstract: In this talk, I’ll survey some of the major open questions in particle physics and make the case that they can best be addressed by a qualitatively new type of particle accelerator: a high-energy muon collider.  Recent progress on long-standing accelerator and detector challenges make such a collider a compelling successor to the LHC.

Prof. Martin Kruczenski

Department of Physics and Astronomy

Purdue University

Host: Anatoly Dymarsky

Title: Two applications of positivity to the theory of strong interactions (QCD)

Abstract: Although the fundamental description of the strong interactions is known, at low energy the theory is strongly coupled and calculations are more difficult as happens in many other areas of physics where perturbation theory does not apply.  On the other hand, recently, positivity conditions have been used to improve and obtain new non-perturbative results in quantum field theory, matrix models, and even classical mechanics.  Motivated by these, I will discuss how to use positivity in the context of gauge theories to find a gauge invariant formulation of lattice gauge theories in terms of Wilson loops, to compute certain low energy scattering amplitudes in two and four dimensions and even to find orbits in classical systems. I will also briefly discuss how these new applications have been fueled by new optimization algorithms developed for similar problems in engineering and finance.

Dr. Alec Tewsley-Booth

Postdoctoral Research Associate

Department of Physics and Astronomy

University of Kentucky

Host: Renee Fatemi and Tim Gorringe

Title: The Second Results from the Fermilab Muon g-2 Experiment

Abstract: On August 10th, 2023, the Muon g-2 Collaboration presented a new experimental value of the positive muon magnetic anomaly, a_μ = (g_μ - 2)/2. From this data set, the first analyzed since our release in 2021, we determine a_μ = 116592057(25) x 10^-11. This result dominates the new experimental world average, a_μ = 116592059(22) x 10^-11, which includes the 2021 result and the final result from Brookhaven in 2006. This talk will cover the experimental apparatus and analysis techniques used to produce the newest result, especially the improvements made that led to the factor of two improvement over the 2021 result. Additionally, we will cover the state of the theory and its tension with experiment, as well as the contributions from the University of Kentucky.

Yuanyuan Su

Assistant Professor

Department of Physics and Astronomy

University of Kentucky

Host: Gary Ferland and Tom Troland

Title: Studying galaxy clusters in multiwavelength, multiscale, and multidisciplinary

Abstract: As the largest gravitational bound systems in the Universe, galaxy clusters are one of the most important probes for testing the standard cosmological models. A typical galaxy cluster contains hundreds to thousands of member galaxies. The space between these galaxies is filled with hot and diffuse plasma -- the intracluster medium (ICM), which constitutes 90% of the baryonic mass and emits strongly in X-rays primarily through bremsstrahlung. ICM provides unique laboratories to study many astrophysical processes, such as the interaction between the hot baryons and the supermassive black hole, the growth of large scale structure, and the enrichment processes of the Universe. In this talk, I will present our recent discovery on galaxy clusters from its centers to the outskirts including the multiphase gas at the brightest cluster galaxies, bow shock in merging clusters, and the chemical composition of the ICM. Our work on active galactic nuclei in cluster member galaxies and machine learning applications will also be discussed. 

Prof. Susan Gardner

Department of Physics and Astronomy

University of Kentucky

Host: Brad Plaster

Title: QCD for New Physics Searches at the Sensitivity Frontier 

Abstract: 

Questions that drive searches for physics beyond the Standard Model  include the physical origin of the cosmic baryon asymmetry and of dark matter. Quark dynamics, as realized through the theory of quantum chromodynamics (QCD), can appear in these studies in very different ways. In this talk, I develop these possibilities explicitly, first describing the role of QCD in ultra-sensitive searches for new physics, particularly at low energies, and then turning to how its features could be exploited in describing the undiscovered universe, along with the essential observational and experimental tests that could confirm them.

Professor Joe Straley

Department of Physics and Astronomy

University of Kentucky

Host: Brad Plaster

Title: TBA

Abstract: TBA

The 2023 Andrew Chamblin Memorial Colloquium

http://andrewchamblin.org/lecture.html

Speaker:  Dr. Vijay Balasubramanian

Professor

University of Pennsylvania

Title:  The entropy of black holes

Abstract:  One of the most famous results of twentieth-century physics states that black holes carry an entropy proportional to the area of their horizons. This entropy formula is universal in general relativity: it applies to black holes with any mass, charge, or rotation, and in any spacetime dimension.  I will describe a recent proposal explaining the microscopic origin and universality of this formula.  The proposal exploits new developments in the study of many-body chaos, thermalization, and quantum dynamics, along with concepts of complexity and information from theoretical computer science, communications theory, and cryptography.  These developments also suggest that the interior of a black hole is causally accessible to external observers, but only if they can perform egregiously complex measurements that are inaccessible under normal conditions.

Dr. Petr Stepanov

Assistant Professor

University of Notre Dame

Title:  Strong Electronic Correlations in Moiré Materials

Abstract: The unexpected discovery of superconductivity in magic angle twisted bilayer graphene (MATBG) immediately generated a wave of intense theoretical and experimental research attracted by its rich phase diagram, which seemingly resembles ones of copper-oxide high-temperature superconductors. Originated in low-energy ¨flat¨ electronic bands, MATBG hosts a collection of exotic phases including but not limited to superconductivity, correlated insulators, topological and magnetic orders. Compared to other strongly-correlated systems, graphene multilayers offer a unique opportunity to tune the charge carrier density in situ and adjust system properties in other ways (for example, by alternating the distance to the gate or varying the dielectric environment), thus offering a potentially faster progress in understanding the underlying microscopic mechanisms governing its strong correlations. In this talk, as an example of such tuneability, I will discuss how the dielectric environment engineering affects the strong correlations in MATBG. Under a close proximity to the graphite gate (i. e. strong Coulomb interaction screening), MATBG exhibits a quenching of correlated insulator phases, while the vacated phase space is taken over by the superconductor domes. This observation demonstrates that the correlated insulating phases in MATBG can be untied from the superconductors in contrast to the case of cuprates, where the pairing occurs in a heavily interacting environment that locally favors the insulating state. In the second part of my talk, I will present an ongoing work revealing local photovoltage generation in magic angle bilayer and trilayer graphene superlattices, studied by cryogenic near-field imaging (cryo-SNOM). Light-matter interactions probed at the nanoscale help us uncover important symmetry breaking patterns, investigate strongly-correlated phases at slightly elevated temperature above the Tc, where ¨strange¨ metal and nematic ordering have been observed, and finally reveal a complex domain structure explained by the strain and twist angle inhomogeneity inherent to the entire class of moiré materials.

Prof. Phillip Phillips

University of Illinois Urbana-Champaign

Host:  Murthy

Title: Beyond BCS: An Exact Model for Superconductivity and Mottness\

Abstract: The Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity described all superconductors until the 1986 discovery of the high-temperature counterpart in the cuprate ceramic materials.  This discovery has challenged conventional wisdom as these materials are well known to violate the basic tenets of the  Landau Fermi liquid theory of metals, crucial to the BCS solution.   Precisely what should be used to replace Landau's theory remains an open question.   The natural question arises: What is the simplest model for a non-Fermi liquid that yields tractable results.  Our work builds[1] on an overlooked symmetry that is broken in the normal state of generic models for the cuprates and hence serves as a fixed point.  A surprise is that this fixed point also exhibits Cooper's instability[2,3].  However, the resultant superconducting state differs drastically[3] from that of the standard BCS theory.  For example the famous Hebel-Slichter peak is absent and the elementary excitations are no longer linear combinations of particles and holes but rather are superpositions of composite excitations.  Our analysis here points a way forward in computing the superconducting properties of strongly correlated electron matter.

[1] E. Huang, G. La Nave, P. Phillips, Nat. Phys., 18, pages511–516 (2022).

[2] PWP, L. Yeo, E. Huang, Nature Physics, 16, 1175-1180 (2020).

[3]J. Zhao, L. Yeo, E. Huang, PWP, PRB, Phys. Rev. B 105, 184509 (2022).