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).

Speaker: Patricia Rankin

Professor and Department Chair

Arizona State University

Department of Physics

Host: Plaster

Title: Physics is Fun! Everyone should do it

Abstract: Patricia Rankin became a physicist because she enjoyed it. She still enjoys it. She remembers being asked as a student why more women didn’t study physics. She can now give a much better answer to that question. This talk looks at how physicists solve problems, and why how we think impacts the demographics of our field. She will discuss how our understanding of what makes people leave physics has evolved and why the focus is now on a process driven approach. She will argue that while the field would benefit from more diversity, what matters to an individual is that they get to do what they enjoy and feel welcome.

Dr. NandiniTrivedi

Professor

Ohio State University

Host: Murthy

Title: Fractionalized excitations in Quantum Spin Liquids and their Detection

Abstract: The 2022 Nobel prize celebrates the detection of entanglement between two photons. Quantum spin liquids (QSLs) are long-range entangled states of matter of billions of interacting qubits or spins that develop in a Mott insulator. The fate of the interacting spins can progress along two paths as the temperature is lowered: the spins can undergo long range ordering, spontaneously breaking the continuous symmetries, leading to a magnetic phase; or the spins can remain disordered but get quantum mechanically entangled with long range patterns of many-body entanglement in the resultant QSL. The possibility of obtaining QSL phases is enhanced by having a low spin and enhanced quantum fluctuations, and frustration arising from the lattice geometry and/or competing spin-spin interactions. Remarkably QSLs harbor fractionalized excitations rather than the conventional spin waves of ordered magnets that carry integer units of angular momentum. In my talk I will identify detectable signatures of these fractionalized excitations in experiments using light and neutrons. These fractionalized excitations are promising candidates to create logical qubits for quantum computation. 

Dr. Heidi Wu

Assistant Professor

Boise State University

Host: Su

Title: Probing Cosmic Acceleration with Galaxy Clusters

Abstract: The accelerated expansion of the Universe is one of the biggest puzzles in physics: Why is gravity repulsive rather than attractive on distance scales larger than a few million lightyears? Cosmic acceleration slows down the growth of structure, and we can use galaxy clusters — the largest gravitationally bound objects in the Universe — to probe the nature of cosmic acceleration.  In this talk, I will first introduce our current understanding of the Universe.  I will then discuss how we use sky surveys of galaxy clusters to measure cosmic acceleration and how several ambitious ground- and space-based missions will revolutionize our understanding of the Universe.

Speaker: Geoff Greene

Professor Emeritus

University of Tennessee

Host: Crawford

Title: The Life and Death of the Free Neutron

Abstract:  The decay of the free neutron is the simplest example of nuclear beta decay and, as such, is the archetype for a wide variety of Weak Interaction processes. These include radioactivity, Big Bang Nucleosynthesis, and energy production in the sun. Additionally, The precise value of the free neutron lifetime, can, along with other data, be used to test the consistency of the Standard Model. Remarkably, the value of neutron lifetime can also help determine the atmospheric composition of Venus. Given the breadth of physics involved, it is  disconcerting to note that, at present, measurements of the neutron lifetime by different methods are inconsistent. In this talk, I will discuss the physics of neutron decay and will review the strategies for the experimental determination of the neutron lifetime. I will discuss some of the experimental challenges and will attempt to provide some illumination of the current discrepant situation. 

Title: Electrify Everything!

Abstract: Making everything run on electricity is a necessary step in the transition from fossil fuels.    Starting that process immediately  is also necessary, and  helpful both to the process and the environment.

Host: Korsch

Title: Trapped-ion optical clocks: Telling time and testing physics at the quantum limit

Abstract: Optical transitions in trapped, laser-cooled ions can provide an extremely well-controlled frequency reference for atomic clocks.  The most stable and accurate atomic clocks now make measurements with total uncertainty approaching 1×10^-18.  The Ion Storage Group at NIST develops optical clocks based on the ¹S₀-³P₀ resonance in ²⁷Al⁺.  To perform precision spectroscopy on this atomic system we use the basic building block of a quantum computer, the two-qubit gate, which transfers information from ²⁷Al⁺ to a second ion species held in the same trap.  I will introduce these systems and present recent frequency comparisons between them and other optical clocks at NIST.   These comparisons provide valuable data for international time/frequency standards and can test our fundamental theories including relativity and the Standard Model.  I will also describe quantum metrology techniques that have allowed us to approach the quantum limit for stability in a ²⁷Al⁺ single-ion clock.