Colloquia are held on Thursdays at 4pm in room 4327 (building 4) of the Stevenson Science Center unless otherwise noted. Click here for directions, or phone the department. A reception with the speaker is held at 3:30pm in Stevenson 6333.
Thursday August 29th 2019 4:00 PM
Carlos Silva, Georgia Institute of Technology
Exciton polarons in two-dimensional organic-inorganic hybrid perovskites
While polarons — charges bound to a lattice deformation induced by strong electron-phonon coupling — are understood to be primary photoexcitations at room temperature in three-dimensional hybrid organic-inorganic perovskite (HOIP) lattices, excitons are the stable quasiparticles in two-dimensional (2D) HOIPs. In this colloquium, I will address the question: are polaronic effects consequential in the exciton properties of these materials? Establishing the role of exciton polarons is a key fundamental issue for the rigorous description of the materials physics of 2D HOIPs. Based on our recent work, I will argue that exciton-polaron effects are manifested in the generally observed spectral fine structure comprised of four distinct, non-degenerate exciton resonances with constant inter-peak energy spacing that varies weakly upon substitution of organic cation. I will discuss the possible role of polaronic effects in establishing the finestructure along with alternative interpretations presented in the literature, including the effects of vibronic structure, Rashba splitting, and exchange interactions. Finally, I will address the consequences of polaronic effects on the quantum dynamics of these materials, relevant for applications in optoelectronics, such as light-emitting diodes, lasers, and polariton spontaneous coherence.
Thursday September 5th 2019 4:00 PM
Thursday September 12th 2019 4:00 PM
Scott Gaudi, Ohio State University
The Demographics of Exoplanets with WFIRST
Measurements of the demographics of exoplanets over a range of planet and host star properties provide fundamental empirical constraints on theories of planet formation and evolution. I will discuss various efforts to measure and synthesize exoplanet demographics over broad regions of parameter space. Because of its unique sensitivity to low mass, long period, and free floating planets, microlensing is an essential complement to our arsenal of planet detection methods. I motivate, and provide expectations for, a microlensing survey with WFIRST, which when combined with the results from Kepler, will yield a nearly complete picture of the demographics of planetary systems throughout the Galaxy
Thursday September 19th 2019 4:00 PMFRANCIS G. SLACK LECTURE
Gerald Gabrielse, Trustees Professor and Director of the Center for Fundamental Physics at Northwestern University
Tabletop Searches for New Physics: a Tale of Two Electron Dipole Moments
The fundamental mathematical description of physical reality, the Standard Model of Particle Physics, is the great triumph and the great frustration of modern physics. The great triumph is that all laboratory measurements are so far consistent with its predictions. The great frustration is that the Standard Model is clearly wrong, or at least significantly incomplete, in that it cannot account for many basic features of our universe. Measurements of the magnetic and electric dipole moments of the electron are crucial tests of the Standard Model. The measured magnetic dipole moment of the electron, the most accurately determined property of an elementary particle, is a test of the Standard Model's most precise prediction. The measured electric dipole moment of the electron tests the relative validity of the dramatically predictions of the Standard Model and of proposed improvements (e.g. supersymmetric models) This work was supported by the USA NSF.
Monday September 23rd 2019 4:00 PM
David Brin, Astrophysicist and Novelist
Our place in the Cosmos and Is Anyone Out There
In both science and literature, the question of ‘others’ can be a mirror illuminating our own origins and plausible destinies. Are we a fluke? Might we be the first to navigate the minefield of existence? Astrophysicist and novelist David Brin will (briefly) survey both what we know and can speculate about life in the universe.
Thursday September 26th 2019 4:00 PM
Les Johnson, NASA
Perspectives at 50: Space Science and Exploration Past, Present, and Future
After the Apollo astronauts landed on the moon, the Space Race ended. The achievements in human space flight continued with the successes of Skylab, the Space Shuttle, and the International Space Station. With the retirement of the Space Shuttle fleet in 2011, America has been relying on Russia to carry its crews into space. Today, we are in the midst of a new Race to Space, with various commercial companies vying to claim the mantle of returning Americans to space in American-made rockets – providing revolutionary changes in the economics of space travel. A similar revolution in cost and capability is occurring in the robotic science community, allowing small businesses, universities, and non-profit research institutions to build and fly small spacecraft with capabilities rivaling those previously in the exclusive domain of governments. Today, for the first time since the 1960’s, there is a sense of unbounded optimism regarding the human future in space and our ability to send our robotic emissaries to the outer reaches of the solar system and beyond.
Thursday October 3rd 2019 4:00 PM
Thursday October 17th 2019 4:00 PMWENDELL HOLLADAY LECTURE
Calen Henderson, IPAC-Caltech
Exoplanet Demographics from Kepler to WFIRST
Over the past decade we have witnessed an acceleration in the pace of exoplanet detection and characterization. In particular, the Kepler space telescope facilitated the first large-scale studies of planet demographics, illuminating trends as a function of both planet radius and orbital period. The nature of the mission, however, led to these results being focused on planetary systems nearby to the Sun and to planets orbiting close-in to their host star. Yet more recently, gravitational microlensing has made myriad advancements with regard to characterizing individual planetary systems and exploring relatively unknown demographic regimes for planets orbiting at larger distances from their host stars, and located farther from the Solar neighborhood, including for free-floating planets not gravitationally tethered to any host star. I will highlight a handful of results, placing them in the context of what we have learned from Kepler. Then I will discuss the anticipated findings from WFIRST, NASA’s next flagship astrophysics mission, which will conduct a large-scale exoplanetary microlensing survey toward the center of the Milky Way.
Thursday October 31st 2019 4:00 PM
Shriram Ramanathan, Purdue University
Quantum materials for brain and biological sciences
The survival instinct is ubiquitous across organisms. Intelligence and cognitive capability however are correlated with the complexity of the nervous system, e.g. neuronal diversity and is enhanced by transfer of evolutionary knowledge and lifelong learning. We will consider examples where such organismic behavior can be realized in programmable quantum materials. Using the metastable perovskite nickelates as a model system, we will discuss insulator-metal transitions that are controlled by hydrogen doping highlighting recent discoveries on electronic structure modulation approaching the predictions of Verwey and Mott. From understanding the binding of the charge carriers to the lattice, we will describe two experiments in nickelates that mimic classic observations in biology, namely habituation in the sea slug Aplysia and ancestral intelligence in sharks. We will conclude with suggestions for future research to design AI machines that can exploit strong Coulomb interactions in ionic lattices.
Thursday November 7th 2019 4:00 PM
Prem Kumar, Northwestern University
Quantum Engineering: A Transdisciplinary Vision
A global quantum revolution is currently underway based on the recognition that the subtler aspects of quantum physics known as superposition (wave-like aspect), measurement (particle-like aspect), and entanglement (inseparable link between the two aspects) are far from being merely intriguing curiosities, but can be transitioned into valuable, real-world technologies with performances that can far exceed those obtainable with classical technologies. The recent demonstration by the Chinese scientists of using a low-earth-orbit satellite to distribute entangled photons to two ground stations that are over a thousand kilometers apart is a stunning technological achievement—direct entanglement distribution over the best available fiber links is limited to a few hundred kilometers—and a harbinger of future possibilities for globally secure communications guaranteed by the power of quantum physics. Harnessing the advantages enabled by superposition, measurement, and entanglement (SME)—the three pillars of quantum physics—for any given application is what is termed quantum engineering in general. In many instances, however, the details of the underlying science (high-temperature superconductivity, photosynthesis, avian navigation, are some examples) is still not fully understood, let alone how to turn the partially understood science into a potentially useful technology. Nevertheless, it has become clear in the last few decades that quantum engineering will require a truly concerted effort that will need to transcend the traditional disciplinary silos in order to create and sustain new breeds of science and technology communities that will be equally versed in quantum physics as they would be in their chosen area of technology. In this talk, I will present my vision for unleashing the potential of quantum engineering, taking quantum communications and networking as an example.
Thursday November 14th 2019 4:00 PMGUY and REBECCA FORMAN LECTURE
Outrageous Acts of Thinking
Dr. Deborah Berebichez - Debbie is an expert in physics, science, innovation, embracing change, media communications and Internet of Things (IoT) and is an expert in Big Data, acting as a chief Data Scientist in NYC. Debbie is also the cohost of Discovery Channel’s Outrageous Acts of Science TV, where she uses her physics background to explain the science behind extraordinary engineering feats. Deborah has also appeared as an expert on the Travel Chanel, NOVA, CNN, FOX, MSNBC, and numerous international media outlets. She has a Ph.D. in physics from Stanford University: the first Mexican woman ever to do so.
Monday November 18th 2019 4:00 PM
Michael Tremmel, Yale University
Dynamic Duos: Supermassive Black Hole Pairs in Galaxy Mergers
I present the first self-consistent prediction for the formation timescale of close Supermassive Black Hole (SMBH) pairs, the precursors to SMBH binaries, following galaxy mergers. Using Romulus25, the first large-scale cosmological simulation to accurately track the orbital evolution of SMBHs within their host galaxies down to sub-kpc scales, we predict that it is relatively rare for galaxy mergers to result in the formation of close SMBH pairs with sub-kpc separation and those that do form are often the result of Gyrs of orbital evolution. The likelihood and timescale to form a close SMBH pair depends on the mass and morphology of the merging galaxies. When galaxies are disrupted during a merger, their SMBHs are deposited on long lived, kpc-scale orbits that result in a population of ‘wandering’ SMBHs. I discuss the implications of these results for predictions of SMBH merger rates and examine the population of wandering SMBHs that our simulations predict should reside in massive halo
Thursday November 21st 2019 4:00 PM
Andrew Mugler, Purdue
Physics of collective cell sensing
The physical limits to chemical sensing have been established and tested for single cells. However, recent experiments have demonstrated that cells can surpass these limits when they communicate. The theoretical limits to the precision of collective sensing are still poorly understood. In this talk, I will discuss three types of cell-cell communication (short-range, long-range, and self-communication) and describe how they alter the physical limits for fundamental sensory tasks, including gradient sensing by epithelial organoids and flow sensing by metastatic cancer cells. This work extends the study of sensory limits to multicellular ensembles and lays the blueprint for a generic theory of collective sensing.
Thursday November 28th 2019 4:00 PMThanksgiving Holidays
Thursday December 5th 2019 4:00 PM
Thomas Weiler, Vanderbilt University
Thursday January 16th 2020 4:00 PM
Jessica Watkins, Vanderbilt University, Department of Teaching and Learning, Peabody College
Problematizing as a scientific endeavor: The importance of students identifying, articulating, and motivating problems
There has been significant attention to students’ problem solving in physics, including what kinds of problems are useful to solve and how to help students learn to solve them. In this talk I argue for the importance of students authoring problems, as work that is central to the discipline of physics. This work, which we call problematizing, involves noticing an inconsistency or gap of understanding, identifying and articulating its precise nature, and motivating a community of its existence and significance. Drawing from scientists’ accounts and philosophy of science, I show the importance of problematizing in physics and how the development of a problem can be a significant scientific achievement. I then present two cases, one from elementary school and another from an introductory physics course, showing that students can problematize as part of their engaging in scientific inquiry. This perspective on the importance of problematizing holds implications for instruction, including the need to make space for students to articulate their confusion before there is a clear question and to acknowledge the role of uncertainty in scientific work.
Thursday January 23rd 2020 4:00 PM
Juan Carlos Idrobo, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory
Honey, I Shrunk the Synchrotron, and the Result is an Electron Microscope: Sensing Magnetic Ordering, Electric Fields and Isotopes at the Atomic and Nanometer Level
Scanning and transmission electron microscopes (S/TEM) are now ubiquitous in materials and biological sciences laboratories. They have radically enhanced our understanding of organic and inorganic matter with the successful development of aberration correctors [1,2], detectors with film-equivalent dynamical range , and more recently, with monochromators capable of achieving sub-10 meV energy resolution spectroscopy . Here, I will present several examples demonstrating how we have exploited these capabilities and solved the pertinent experimental challenges to probe materials behavior at the nanometer and atomic scales. Specifically, I will show how by utilizing the phase of the electron probe one can reveal the anti-ferromagnetic order of complex-oxide materials , and explore the ferromagnetic strength at the interfaces of thin-film complex-oxide heterostructures  at the atomic level. I will also explain how the new generation of monochromators, combined with aberration-corrected STEM, can be used (i) as a primary thermometer (without requiring any previous knowledge of the sample) ; (ii) to study minute volumes of liquid water ; (iii) to detect site-specific isotopic labels in amino acids at the nanometer scale . Additionally, I will show how one can detect the electric field of individual atomic columns of heavy and light elements, at the sub-Angstrom scale, by using an ultra-low noise SCMOS detector in the diffraction plane , and how one can detect anti-Fano resonances in plasmonic nanostructures . Lastly, I will discuss potentially relevant new challenges that electron microscopy will need to resolve as it enters the forthcoming quantum information era. Could we detect a superconducting transition? Could we spectroscopically measure cryogenic temperatures with sub Kelvin precision? Could we measure the specific heat and thermal conductivity of materials? Could we detect minute concentrations of isotopic elements and perform radiocarbon dating at the nanoscale? These questions will be addressed and further elaborated during the presentation . References:  J. Zach and M. Haider, Optik 99 (1995), p. 112.  O. L. Krivanek, et al, Institute of Physics Conference Series 153 (1997), p. 35.  A. R. Faruqi, R. Henderson, Curr. Opin. Struc. Biol. 17 (2007), p. 549.  O. L. Krivanek, et al., Phil. Trans. R. Soc. A 367 (2009), p. 3683.  J. C. Idrobo, et al., Adv. Struc. Chem. Img. 2 (2016), p. 5.  J. C. Idrobo, et al., unpublished (2020).  J. C. Idrobo, et al., Phys. Rev. Lett. 120 (2016), p. 095901.  J. R. Jokisaari, et al., Adv. Mater. 30 (2018), p. 1802702.  J. A. Hachtel, et al., Science 363 (2019), p. 525.  J. A. Hachtel, et al., Adv. Struc. Chem. Img 4 (2018), p. 10.  K. Smith, et al., Phys. Rev. Lett. 123, (2019), p. 177401.  This research was supported by the Center for Nanophase Materials Sciences, which is a Department of Energy Office of Science User Facility, and instrumentation within ORNL's Materials Characterization Core provided by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy.
Thursday January 30th 2020 4:00 PMFrancis G. Slack Lecture
Barry Barish, Caltech
Probing the Universe with Gravitational Waves
The discovery of gravitational waves, predicted by Einstein in 1916, is enabling both important tests of the theory of general relativity, and the birth of a new astronomy. Modern astronomy, using all types of electromagnetic radiation, is giving us an amazing understanding of the complexities of the universe, and how it has evolved. Now, gravitational waves and neutrinos are beginning to give us the opportunity to pursue some of the same astrophysical phenomena in very different ways, as well as to observe phenomena that cannot be studied with electromagnetic radiation. The detection of gravitational waves and the emergence and prospects for this exciting new science will be explored.
Thursday February 6th 2020 4:00 PM
Zina Cinker, National Graphene Association
Monday February 10th 2020 3:00 PMNote change in Date and Time
Michael Murrell, Yale University
Thursday February 13th 2020 4:00 PM
Tamara Bogdanovic, Georgia Tech
Thursday February 20th 2020 4:00 PM
Thomas Ullrich, Brookhaven National Laboratory
Host:S. V. Greene
Thursday February 27th 2020 4:00 PM
Nina Balke, ORNL
Thursday March 5th 2020 4:00 PMSpring Holidays
Thursday March 12th 2020 4:00 PM
Thursday March 19th 2020 4:00 PM
Jeffrey Nico, NIST
Thursday March 26th 2020 4:00 PM
Jason Dexter, JILA
Thursday April 2nd 2020 4:00 PM
Julie Hogan, Bethel University
CMS Particle Flow: the LEGO tutorial and searches for new massive quarks
The Compact Muon Solenoid detector at CERN's Large Hadron Collider uses a method called "particle flow" to interpret electronic signals in detector elements as particles like electrons or muons. This critical software is rarely learned in detail by young CMS researchers. I will share an engaging new hands-on tool developed for summer tutorials at Fermilab: the Particle Flow LEGO Experience. Then I will present recent searches for new physics particles called "vector-like quarks", which decay to a variety of massive quarks and bosons. In these searches we connect the particle flow information from showers of quark-based particles with machine learning algorithms to probe for evidence of new physics.
Host:S. Starko and R. Scherrer
Thursday April 9th 2020 4:00 PM
Anthony Mezzacappa, Oak Ridge National Laboratory
Nucleosynthesis in Supernovae
Thursday April 16th 2020 4:00 PM
Duncan Lorimer, WVU