Physics and Astronomy Colloquium Series

Colloquia are presented on Thursdays at 3:45 p.m. in the Physics Research Building, room 245 (unless otherwise noted). Refreshments are served at 3:30 p.m.

View upcoming physics colloquia

Past and present colloquia

  • Fall 2019

    September 19, 2019

    James Wells, University of Michigan

    Seeking clues on why matter won over antimatter

    Abstract

    One of the most intriguing mysteries of nature is why there is more matter in the universe than anti-matter given that the basic laws of particle physics do not appear to allow for it. One promising direction of explanation attacks the conservation of baryon number, which I will argue is one of the most vulnerable principles in fundamental physics. Forthcoming proton decay and neutron oscillations experiments may reveal much about just how the universe managed to make us and not anti-us.

    September 26, 2019

    Aurelia Honerkamp-Smith, Lehigh University 

    Membrane protein transport: Balancing advection and diffusion

    Abstract

    The fluidity of lipid membranes is essential to their biological function: cell membranes are required to be flexible, self-healing, and deformable. An additional consequence of membrane fluidity is that both lipids and proteins are highly mobile, which makes it possible for lipid-anchored proteins to travel long distances across the surface of cells. The significance of this lateral mobility for flow mechanosensing has not yet been determined. We study the mechanics of lateral membrane protein transport by flow in an in vitro model of the cell plasma membrane, lipid bilayers supported on glass. We prepare supported bilayers formed from individual GUVs inside microfluidic channels in order to study transport of membrane-anchored proteins. We observe and fit dynamic protein concentration gradients, which allow us to define protein mobility relative to a stationary lipid membrane.

    October 3, 2019

    Dean Lee, Michigan State University

    Lattice Simulations of Nuclear Structure and Thermodynamics

    Abstract

    In this talk I give an introduction to the method of lattice effective field theory, which is the combination of effective field theory and numerical lattice techniques.  I then discuss several recent results from the Nuclear Lattice Effective Field Theory Collaboration.  The first is the connection between microscopic nuclear forces and nuclear structure.  This centers on a basic question of what are the truly essential features of the nuclear force needed to produce the observed properties of atomic nuclei.  The second is the development of first principles simulations of the thermodynamics of nuclei and nuclear matter.

    October 17, 2019

    William Llope, Wayne State University

    Correlations in relativistic heavy-ion collisions

    Abstract

    In modern collider experiments, scientists collide atomic nuclei going at the speed of light in order to create large systems of deconfined quarks and gluons called the quark-gluon plasma (QGP). The scientists try to measure every particle produced in the collision in order to try to completely reconstruct the physics of the QGP, the state of our universe a few microseconds after the Big Bang. By measuring as many particles as possible per collision in a wide acceptance, scientists can explore multi-particle correlations, which indicate both prosaic reaction mechanisms (like momentum conservation) and potentially more exotic (and as yet undiscovered) mechanisms such as a critical opalescence - a beam-energy localized growth of long-range correlations signalling the existence of a critical point in the nuclear matter phase diagram. My two research groups work in two different but related directions. One group explores these correlations, and their integrals called the "fluctuations," by analyzing the experimental data collected by the STAR experiment at RHIC. My other group has been building new large-scale detector upgrades to improve the data coming from these modern experiments. The status and outlook of these efforts will be presented.

    October 24, 2019

    Indara Suarez, Boston University

    Desperately Seeking SUSY

    Abstract 

    Questions surrounding the measured value of the Higgs mass as well as astrophysical evidence for Dark Matter suggest that new particles and/or interactions are awaiting discovery. With the significant increase in collision energy and the large datasets of the LHC Run-2, we have continued our hunt for physics beyond the Standard Model by developing new strategies and machine-learning tools.  I will discuss the ongoing searches for Supersymmetric partners of the top quark, called top squarks or "stops", and how their discovery could shed light onto the nature of the lightness of the Higgs mass and Dark Matter.  My talk will focus on the detector upgrades that laid the foundation for exploiting the Run-2 data, the most recent results, and possible future directions in our search for new physics.

    October 31, 2019

    Kate Scholberg, Duke University

    Detecting the Tiny Thump of the Neutrino

    Abstract

    Neutrinos interact only rarely with matter.   Coherent elastic neutrino-nucleus scattering (CEvNS) was first predicted in 1974; it’s a process in which a neutrino scatters off an entire nucleus.  By neutrino standards, CEvNS occurs frequently, but it is tremendously challenging to see. The only way to observe it is to detect the minuscule thump of the nuclear recoil. CEvNS was measured for the first time by the COHERENT collaboration using the unique, high-quality source of neutrinos from the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory.   This talk will describe COHERENT's recent measurement of CEvNS, the status and plans of COHERENT's suite of detectors at the SNS, and the physics we will learn from the measurements.

    November 7, 2019

    Elena Gallo, University of Michigan

    A census of the black hole population in nearby low mass galaxies

    Abstract

    It is commonly accepted that a supermassive black hole – as massive as several millions or even billions Suns – sits at the center of every galaxy that is as large as (or larger than) the Milky Way galaxy. Additionally, the black hole is thought to play a critical role in shaping the large-scale properties of the galaxy it lives in. It does so by blowing galaxy-scale outflows of energy and matter, which in turn affect the fate of its host galaxy gas reservoir, and, ultimately, its ability to form stars. Whether a similar feedback mechanism takes place is not obvious when it comes to dwarf galaxies, i.e. galaxies that are one tenth of a Milky Way, or smaller. Even though dwarfs make up the overwhelming majority of the galaxy population out there, it is not clear whether all dwarf galaxies host a massive black hole at their center, and, if they do, whether the properties of those black holes, and chiefly their masses, scale with the overall galaxies’ properties the same way they do in larger galaxies. Part of the uncertainty has to do with the fact that standard “dynamical techniques”, which use the motion of gas and stars around the black hole to infer its presence, rely on being able to spatially resolve the black hole's gravitational sphere of influence. Yet the fraction of dwarf galaxies that host a massive black hole is of great interest to astronomers. The reason goes beyond simple demographics; the “black hole occupation fraction” in today’s dwarf galaxies is expected to be sensitive to the very mechanism through which these giant black holes were born when the Universe was still in its infancy. Surprisingly, this remains an open question. During this talk, I will present recent results from my group addressing these questions, in an effort to build a complete census of the population of nearby, massive black holes.

    December 5, 2019

    Michael Strickland, Kent State University

    Title of presentation/talk

    Abstract

    Description of abstract.

  • Winter 2018

    January 18, 2018

    Shanshan Cao, Wayne State University

    Probing the Quantum Chromodynamic fluid with relativistic nuclear collisions

    Abstract: Nuclear matter is heated beyond two trillion degrees in relativistic heavy-ion collisions and becomes a strongly coupled plasma of quarks and gluons. This highly excited quark-gluon plasma (QGP) matter displays properties of the perfect fluid and is believed similar to the state of the early universe microseconds after the big bang. In this talk, high-energy particles and jets are utilized to probe the QGP properties. A linear Boltzmann transport coupled to hydrodynamic model is established to describe the strong interaction between energetic partons and the QGP. This includes diverse microscopic processes for both massless and massive parton scatterings, and provides a simultaneous description of the nuclear modification of heavy and light flavor hadrons observed at the RHIC and LHC experiments. To precisely extract transport coefficients of the QGP, a statistical analysis framework that includes machine learning and Bayesian methods is developed, which brings a paradigm shift in statistical comparisons between theory and experiment.

     

    January 25, 2018

    ChunNing (Jeanie) Lau, Ohio State University

    Spin, Charge and Heat Transport in Low-Dimensional Materials

    Abstract: Low dimensional materials constitute an exciting and unusually tunable platform for investigation of both fundamental phenomena and electronic applications. Here I will present our results on transport measurements of high-quality few-layer phosphorene devices, the unprecedented current carrying capacity of carbon nanotube "hot dogs", and our recent observation of robust long distance spin transport through the antiferromagnetic state in graphene.

    About the speaker: Dr. Chun Ning (Jeanie) Lau is a Professor in the Department of Physics at The Ohio State University. She received her BA in physics from the University of Chicago in 1994, and Ph.D. in physics from Harvard in 2001. She was a research associate at Hewlett Packard Labs in Palo Alto from 2002 to 2004, before joining the University of California, Riverside in 2004 as an assistant professor. She was promoted to associate professor in 2009 and full professor in 2012. Starting January 2017 she moved to The Ohio State University. Her research focuses on electronic, thermal and mechanical properties of nanoscale systems, in particular, graphene and other two-dimensional systems.

     

    January 30, 2018

    Vladimir Skokov, Brookhaven National Lab

    Quantum ChromoDynamics in extreme conditions

    Abstract: In my talk, I discuss two landscapes of Quantum ChromoDynamics (QCD), the theory of strong interactions, in extreme conditions. I start with hot and dense QCD, which can be probed in the collisions of heavy-ions at high energy. The goal of the heavy-ion program is to map and study the QCD phase diagram and establish the existence of a conjectured critical point in QCD. The identification of this prominent landmark in the phase diagram is possible owing to its unique signature. I argue that recent experimental measurements agree with the theoretical expectations and, if confirmed, may lead to the discovery of a QCD critical point. I then turn to the landscape of cold QCD to be probed at a future Electron-Ion Collider. I discuss one of the exciting features which is the linear polarization of strong quasi-classical gluon fields in an unpolarized nucleus.

     

    February 1, 2018

    Li Yan, McGill University

    A droplet of QGP in the little bang

    Abstract: One of the fundamental questions in high energy nuclear physics is how to understand the dynamics of matter systems dominated by strong interactions. Especially, in systems where temperatures are comparable to the QCD energy scale (~1012 K), such as the universe in the first microseconds after Big Bang, or in high energy heavy-ion collisions carried out at RHIC and the LHC (the Little Bang), our interest is in a novel state of matter – quark-gluon plasma (QGP). One of the significant properties of QGP is its perfect fluidity. Actually, the value of shear viscosity over entropy density ratio of QGP has been found to be very close to a theoretical lower bound. The fluidity the QGP plays an essential role in the present studies of heavy-ion experiments. QGP evolution dominates the observed correlation behaviors of the produced particles in nucleus-nucleus collisions (large colliding systems), proton-lead and even proton-proton collisions (small colliding systems). In this talk, I will demonstrate how the idea of QGP fluidity emerges from the observed phenomena in experiments. I will also explain how a "standard model" of heavy-ion collisions based on relativistic hydrodynamics is challenged by the fluid behavior in recent small colliding systems.

     

    February 8, 2018

    Chun Shen, Brookhaven National Lab

    Going with the flow — the nuclear phase diagram at the highest temperatures and densities

    Abstract: The nuclear matter has a complex phase structure, with a deconfined Quark-Gluon Plasma (QGP) expected to be present under conditions of extreme pressure and temperature. The hot QGP filled the universe about few microseconds after the Big Bang. This hot nuclear matter can be generated in the laboratory via the collision of heavy atomic nuclei at high energy. I will review recent theoretical progress in studying the transport properties the QGP. Recently, the Relativistic Heavy-Ion Collider (RHIC) conducted the beam energy scan experiments. It offered a unique opportunity to study the nuclear phase diagram in a hot and baryon-rich environment. I will focus on the development of a comprehensive framework that is able to connect the fundamental theory of strong interactions with the RHIC experimental observables. This dynamical framework paves the way for quantitative characterization of the QGP and for locating the critical point in the nuclear phase diagram. These studies will advance our understanding of strongly interacting many-body systems and build interconnections with other areas of physics, including string theory, cosmology, and cold atomic gases.

     

    February 15, 2018

    Mauricio Guerrero, North Carolina State University

    Out of equilibrium dynamics: Lessons from Nuclear Collisions

    Abstract: The current knowledge of the universe is highly constrained without understanding the formation of baryonic matter widely observed today. It is then required to know the precise details of the transition where a highly dense plasma composed by quarks, antiquarks, and gluons combine to form hadrons. Ultrarelativistic heavy ion experiments can recreate non-equilibrium extreme conditions of the early universe by colliding heavy nuclei moving nearly at the speed of light. One of the major scientific discoveries of this century is the observation of a tiny, short-lived quark-gluon plasma (QGP). This extreme state of matter behaves like a liquid with a very small viscosity. Recently,  we have learned that the perfect fluidity property, observed first in nucleus-nucleus collisions, also extends to proton-nucleus and proton-proton collisions. The  "nearly perfect liquid" behavior of the QGP has opened up a new avenue for studying transport properties of strongly interacting systems. Nonetheless, these experimental findings challenge the theorists to develop better models which include the non-equilibrium evolution of the expanding nuclear matter created in those collisions. In this talk, I will review the 'standard model picture' of heavy ion collisions and present some recent theoretical studies which attempt to explain the unreasonable phenomenological success of fluid dynamical models in far from local equilibrium situations. I shall pose several unanswered questions about the QGP which emerge from these new theoretical developments and discuss how in the next few years, future experimental programs at large baryon densities and energy regimes will herald a new era of discovery and unraveling of the secrets of QGP.

     

    February 22, 2018

    Hong Guo, McGill University

    Electronic States of the Moiré superlattice

    Abstract: Two-dimensional (2D) van der Waals (vdW) heterostructures have attracted great attention in the past five years. By stacking different 2D materials to bond via the vdW force, these artificial heterostructures provide interesting and new material phase space for exploration. In this talk, I shall focus on one aspect of the 2D vdW materials: the Moiré pattern. In visual arts, Moiré pattern is an optical perception of a new pattern formed on top of two similar stacking patterns. In 2D vdW heterostructures, the Moiré pattern is a physical superlattice which brings about novel electronic properties. To theoretically predict the physical properties of the Moiré superlattice, systems containing more than ten thousand atoms often need to be analyzed by first principles. In this talk, I shall begin by briefly discussing how one may break the "size limit" so that very large first principles simulations within the density functional theory can be carried out. Afterward, I shall present and discuss some of the calculated novel properties of the Moiré superlattice: the emergence of a secondary Dirac cone, the suppression of the carrier mobility, and the formation of multiple helical valley currents, on various 2D vdW heterostructure materials. Some of these properties can well be the basis of potential applications.

    About the speaker: Dr. Hong Guo obtained B.Sc. in Physics at the Sichuan Normal University in China and Ph.D. in theoretical condensed matter physics at the University of Pittsburgh. In 1989, he joined the faculty of the Physics Department, McGill University in Montreal Canada. He is currently a James McGill Professor of Physics. His research includes quantum transport theory, nanoelectronic device physics, nonequilibrium phenomena, materials physics, density functional theory, mathematical and computational physics. He was elected to Fellow of the American Physical Society in 2004, and Fellow of the Royal Society of Canada (Academy of Sciences) in 2007. He received the Killam Research Fellowship Award from the Canadian Council for the Arts in 2004; the Brockhouse Medal for Excellence in Experimental or Theoretical Condensed Matter Physics of the Canadian Association of Physicists in 2006; and the CAP-CRM Prize in Theoretical and Mathematical Physics from Canadian Association of Physicists in 2009.

     

    March 2, 2018

    David Ceperley, University of Illinois at Urbana-Champaign, and member of the National Academy of Sciences

    How can we model the hydrogen inside Jupiter and Saturn?

    Abstract: Jupiter, Saturn and a host of newly discovered exoplanets are thought to be composed largely of hydrogen and helium. To understand the planets, we need properties of hydrogen and helium under the extreme conditions of temperature and pressure inside those planets, conditions hardly accessible to laboratory measurements. I will describe how we use high-performance computers to calculate those properties and thus help understand some of the most important objects in the Universe.

    About the speaker: Dr. David Ceperley is the Founder and Blue Waters Professor of Physics at the University of Illinois Urbana-Champaign, and a member of the National Academy of Sciences. He received his BS in physics from the University of Michigan in 1971 and his Ph.D. in physics from Cornell University in 1976. After one year at the University of Paris and a second postdoc at Rutgers University, he worked as a staff scientist at both Lawrence Berkeley and Lawrence Livermore National Laboratories. In 1987, he joined the Department of Physics at Illinois. He was a staff scientist at the National Center for Supercomputing Applications from 1987 until 2012. Professor Ceperley is a Fellow of the American Physical Society and a member of the American Academy of Arts and Sciences and was elected to the National Academy of Sciences in 2006. He has received many honors and awards.

     

    March 6, 2018

    LongGang Pang, Lawrence Berkeley National Laboratory

    Exploring the quantum chromodynamics phase transition with deep learning 

    Abstract: The state-of-the-art pattern recognition method in machine learning (deep convolution neural network) has been used to classify two different phase transitions between normal nuclear matter and hot-dense quark-gluon plasma. Big amount of training data is prepared by simulating heavy ion collisions with the most efficient relativistic hydrodynamic program CLVisc. High-level correlations of particle spectra in transverse momentum and azimuthal angle learned by the neural network are quite robust in deciphering the transition type in the quantum chromodynamics phase diagram. Through this study, we demonstrated that there is a traceable encoder of the phase structure that survives the dynamical evolution and exists in the final snapshot of heavy ion collisions and one can exclusively and effectively decode this information from the highly complex output using machine learning.

     

    March 8, 2018

    Christoph Naumann, Indiana University - Purdue University Indianapolis

    Probing membrane protein organization and dynamics in planar model membranes using single molecule-sensitive confocal detection techniques 

    Abstract: The organization and distribution of proteins in the plasma membrane is widely known to influence membrane protein functionality. However, it remains challenging to decipher the underlying mechanisms that regulate membrane protein properties in the complex environment of cellular membranes. To overcome these challenges, an experimental strategy is discussed, in which the distribution, oligomerization state, and mobility of membrane proteins can be explored in a planar polymer-tethered lipid bilayer of well-defined lipid compositions using single molecule-sensitive confocal detection strategies. Results from such model membrane experiments are presented, which explore the influence of native ligands, bilayer asymmetry, and cholesterol content on the sequestration/oligomerization of urokinase plasminogen activator receptors (uPAR) and integrins [1-4]. Moreover, dual-color confocal experiments are described, which provide information about the formation and composition of uPAR-integrin complexes and the role of membrane cholesterol therein. Polymer-tethered lipid bilayer systems, comprised of phospholipids and lipopolymers, are also characterized by remarkable materials properties, which make them suitable as cell surface-mimicking substrates for the analysis of adhesion and spreading of plated cells. To illustrate the feasibility of such an application, we discuss the assembly of cadherin chimera into clusters on the surface of a polymer-tethered lipid bilayer substrate to form stable cell-substrate cadherin linkages underneath migrating C2C12 myoblasts [5]. Cluster tracking experiments reveal the cytoskeleton-regulated long-range mobility of cell-substrate linkages, thereby displaying remarkable parallels to the dynamics of cadherin-based cell-cell junctions.

    [1] A. P. Siegel et al. (2011) Biophys. J. 101, 1642.
    [2] N. F. Hussain et al. (2013) Biophys. J. 104, 2212.
    [3] Y. Ge et al. (2014) Biophys. J. 107, 2101.
    [4] Y. Ge et al. (2018) Biophys. J. 114, 158.
    [5] Y. Ge et al. (2016) Soft Matter 12, 8259.

     

    March 22, 2018

    W.J. Llope, Wayne State University

    How to give a great talk – tips for success and traps to avoid

    Abstract: Whether your future lies in academia or industry, you will have opportunities to present your recent work while standing in front of an audience of interested people. Giving a good talk is a very powerful advertisement of you and your efforts, and, if you can properly enthuse the audience during your talk, the subsequent discussions can be very helpful for your future work. Great talks come in many forms, but all share a few key positive aspects and all avoid some (unfortunately rather common) pitfalls. This colloquium will share some tips from what I've learned over the years while watching thousands of talks, and giving a few myself. This presentation is specifically aimed at our students and postdocs, although the faculty are of course welcome to share their insights as well. The atmosphere will be informal and an open discussion, especially with our younger colleagues, will be encouraged.

     

    March 29, 2018

    Vladimir Chernyak, Department of Chemistry, Wayne State University

    Integrability in Non-Equilibrium Quantum Dynamics

    Abstract: Nonequilibrium quantum dynamics, i.e., quantum evolution with time-dependent Hamiltonians, iħ ∂Ψ(t)/∂t = Ĥ(t)Ψ(t), as of today draws considerable attention, both in experimental and theoretical research. The simplest model with Ĥ(t)=A+Bt, and A and B being 2×2 real hermitian matrices, known as the Landau-Zener (LZ) problem has an exact solution in special functions, with the scattering matrix S, expressed in term of Gaussians and Euler Gamma-function. In the general N-dimensional case, known as Multilevel LZ (MLZ) problem, exact solutions are not available. However, for a certain class of MLZ problems that satisfy certain phenomenologically determined "integrability" conditions, including, but not limited to Demkov-Osherov (DO), Generalized Bow-Tie (GBT), and Tavis-Cummings (TC), the scattering matrix can be represented in a factorized form, with the elementary scattering events being represented in terms of the standard LZ matrix, which is the first aspect of integrability; in other words the semiclassical expressions become exact.

    In this talk we reveal the reason that stands behind the aforementioned factorization: Each integrable MLZ problem can be embedded into a system of M linear first-order differential equations with respect to M-dimensional time, that satisfy the consistency conditions, the latter having a form of the zero-curvature conditions, which is the second and dynamical aspect of integrability.

    We further apply our approach to obtain an exact solution for the BCS model that does not belong to the MLZ class, but rather describes decay of the initial strongly correlated state of Ns quantum spins (in the thermodynamic Ns→∞ limit the model becomes a non-trivial field theory) into an uncorrelated counterpart when the spin-spin interaction is switched off, and generally in a non-adiabatic fashion. The obtained exact solution shows an amazing property: The ground state in the strongly correlated phase "dissociates" into a Gibbs distribution in a completely integrable way, without any chaos or bath involved. We demonstrate that the aforementioned result is a third aspect of integrability, which is the natural appearance of the structures, usually associated with quantum integrability in a form of algebraic Bethe Ansatz, including the Yang-Baxter-Zamolodchikov (YBZ) equation, Artin's Braid Group, and quantum group SUq(2).

    The presentation will be given in an intuitive fashion, all mathematical structures involved will be explained using the terms, which are common for a broad physics audience.

     

    April 5, 2018

    Prof. Aaron Pierce, Director of the Leinweber Center for Theoretical Physics at the University of Michigan

    Dark Matter: WIMPS and Beyond

    Abstract: The identity of the Dark Matter that dominates the matter density of the universe remains a mystery.  Increasingly sophisticated experiments have begun to probe some of the best-motivated models of dark matter.  I will review the theoretical status of one such paradigm, so-called Weakly Interacting Massive Particle (WIMP) Dark Matter, with particular emphasis on the implications of direct detection experiments.  We will see that while the paradigm is alive and well, it is under non-trivial pressure, particularly in specific implementations, such as supersymmetry. This warrants searches for other types of Dark Matter.  I will very briefly discuss a few such searches, including a new possibility of using the LIGO gravitational wave detector as a dark matter detector.

     

    April 19, 2018: Vaden Miles Lecture

    J. Michael Kosterlitz, Brown University (2016 Nobel Prize in Physics)

    Topological Defects and Phase Transitions - A Random Walk to the Nobel Prize

    Abstract: This talk is about my path to the Nobel Prize and reviews some of the applications of topology and topological defects in phase transitions in two-dimensional systems for which Kosterlitz and Thouless split half the 2016 Physics Nobel Prize. The theoretical predictions and experimental verification in two-dimensional superfluids, superconductors and crystals will be reviewed because they provide very convincing quantitative agreement with topological defect theories.

    About the speaker: Dr. J. Michael Kosterlitz is a theoretical physicist recognized for his work with David J. Thouless on the application of topological ideas to the theory of phase transitions in two-dimensional systems with a continuous symmetry. The theory has been applied to thin films of superfluid 4He, superconductors and to melting of two-dimensional solids. This work was recognized by the Lars Onsager prize in 2000, membership in the AAAS 2007, and by the 2016 Nobel Prize in Physics. Dr. Kosterlitz graduated from Cambridge University earning a BSc in physics in 1965, an MA in 1966, and received a D. Phil. from Oxford in 1969. He was a postdoctoral fellow at Torino University, Italy, in 1970 and at Birmingham University, U.K., from 1970-73. There he met David Thouless and together they did their groundbreaking work on phase transitions mediated by topological defects in two dimensions. He was a postdoctoral fellow at Cornell in 1974, on the faculty at Birmingham 1974-81, Professor of Physics at Brown University 1982 – present, and elected to the National Academy of Sciences in 2017.

  • Fall 2018

    September 13, 2018

    Lu Li, University of Michigan

    Quantum Oscillations of Electrical Resistivity in an Insulator

    Abstract: In metals, orbital motions of conduction electrons are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators, in which all the electrons are localized. Here we report a notable exception in an insulator — ytterbium dodecaboride (YbB12). The resistivity of YbB12, despite much larger than that of usual metals, exhibits profound quantum oscillations under intense magnetic fields.

    This unconventional oscillation is shown to arise from the insulating bulk, instead of conducting surface states. The large effective masses indicate strong correlation effects between electrons. Our result is the first discovery of quantum oscillations in the electrical resistivity of a strongly correlated insulator and will bring crucial insight to the understanding of the ground state in gapped Kondo systems.

     

    September 20, 2018

    Prashant Padmanabhan, Los Alamos National Lab

    From plasmons to skyrmions: The ultrafast dynamics and control of novel excitations and materials

    Abstract: Over the last several decades, advances in ultrafast spectroscopy have enabled us to investigate fundamental phenomena associated with the electronic, lattice, and spin degrees of freedom in condensed matter systems at their intrinsic time-scales. Moreover, intense femtosecond pulses allow us to drive materials far from equilibrium. This provides us with access to states that are often difficult, or even impossible, to probe under normal thermodynamic conditions.

    As such, we can now examine the subtleties of exotic excitations, elucidate the microscopic coupling mechanisms between competing subsystems, and transiently manipulate the fundamental properties of novel materials. This talk will focus on such efforts in systems spanning prototypical semiconductors to quantum materials. Specific topics include massless collective excitations of multi-component plasmas, hole scattering dynamics in incipient ferroelectrics, and the optical control of low energy excitations in topologically protected spin textures.

     

    September 27, 2018

    Nagesh Kulkarni, Quarkonics Inc.

    From Ph.D. to CEO: An Entrepreneurial Journey

    Abstract: A Physics education provides general skills in problem-solving, teamwork, and knowledge in cutting--edge technologies. Add some business skills and a physicist can become an entrepreneur. I will talk about my entrepreneurial journey and share my experiences and thoughts on how scientists can play a significant role in shaping the global economy, change the game, and create tremendous value for society by leveraging their unique analytical thinking and problem-solving skills, networking, and specialized knowledge.

     

    October 4, 2018

    Yaqiong Xu, Vanderbilt University

    Carbon-Based Nanomaterials for Biosensing

    Abstract: Carbon-based nanomaterials, such as carbon nanotubes (CNTs) and graphene, have gained significant interest as one of the most promising materials in biological applications due to their unique physical and chemical properties. Recently we have developed an optoelectronic probing system, combining CNT/graphene transistors with scanning photocurrent measurements, fluorescence microscopy, and optical trapping techniques to investigate the molecular interface between CNTs/graphene and biological systems. We have directly measured the binding force between a single DNA molecule and a CNT in the near-equilibrium regime, where two aromatic rings spontaneously attract to each other due to the noncovalent forces between them. We have also integrated graphene-based scanning photocurrent microscopy with microfluidic platforms to investigate the electrical activities of individual synapses of primary hippocampal neurons. I will conclude by summarizing the remaining research challenges that must be surmounted in order to bring carbon-based nanomaterials into future biological applications.

     

    October 11, 2018

    Sergio E. Ulloa, Ohio University

    Putting Things on Top of Other Things (Proximity effects in 2D materials)

    Abstract: Proximity effects such as those produced when depositing graphene on a transition metal dichalcogenide substrate are expected to change the dynamics of the electronic states in graphene, inducing spin-orbit coupling and staggered potential effects. Putting things on top of other things is promising and going strong in 2D materials!
    In this talk, I will describe some of the expectations of combining different layered materials. In particular, I will show how an effective Hamiltonian that describes different symmetry breaking terms in graphene, while preserving time reversal invariance, shows that a new topological insulator may be created by stacking "trivial" materials and applying strong electric fields. These new systems may exhibit quantum spin Hall and valley Hall effects in different conditions [1].

     [1] A.M. Alsharari, M.M. Asmar and S.E. Ulloa, Phys. Rev. B 94, 241106(R) (2016); and Phys. Rev. B 97, 241104(R) (2018).

     

    October 18, 2018

    Igor Žutić, University at Buffalo

    Proximity Effects in van der Waals Materials

    Abstract: Advances in heterostructures and atomically thin van der Waals materials, such as graphene, suggest a novel approach to systematically design materials. A given material can be transformed through proximity effects whereby it acquires properties of its neighbors, for example, becoming superconducting, magnetic, topologically nontrivial, or with an enhanced spin-orbit coupling [1]. Such proximity effects not only complement the conventional methods of designing materials by doping or functionalization but also can overcome their various limitations. In proximitized materials, it is possible to realize properties that are not present in any constituent region of the considered heterostructure. While the focus is on magnetic proximity effects with their applications in spintronics [2-4], the outlined principles also provide a broader framework for employing other proximity effects to tailor materials and realize unexplored phenomena.

    1. I. Žutić et al., Mater. Today, (2018), arxiv:1805.07942, https://doi.org/10.1016/j.mattod.2018.05.003
    2. P. Lazić et al., Phys. Rev. B 93, 241401(R) (2016)
    3. B. Scharf et al., Phys. Rev. Lett. 119, 127403 (2017)
    4. J. Xu et al., Nat. Commun. 9, 2869 (2018)

     

    November 1, 2018

    Weihong Qiu, Oregon State University

    Kinesin-14s: Moving into a New Paradigm

    Abstract: Kinesin-14s are microtubule-based motor proteins that play important roles in cell division. They were originally thought to be minus-end-directed nonprocessive motors that exhibit directional preference toward the microtubule minus ends in multi-motor ensembles but are unable to generate processive (continuous) motility on single microtubules as individual motors. During the past five years, we and others have discovered several "unconventional" kinesin-14 motors that all contain the ability to generate processive motility as individual motors on single microtubules. In this talk, I will present a series of unexpected yet exciting findings from my lab that have markedly expanded current view of the design and operation principles of kinesin-14 motors.

     

    November 27, 2018

    Ron Soltz, Lawrence Livermore National Lab

    Evaluating the Iran Nuclear Deal

    Abstract: The Iran Nuclear Deal evokes strong reactions. It has been called "The Worst Deal Ever" as well as "The best option for preventing Iran from obtaining a nuclear weapon. Otherwise known as the "Joint Comprehensive Plan of Action", the JCPOA has led to much debate, even if little of it has been substantive. Put into effect in 2015, the JCPOA continues to influence the behavior of six of the seven signatories, the seventh having formally withdrawn 2018, reimposing sanctions in May and November. In the history of international agreements, it is truly unique, but as it stands at the intersection of science and policy, it is also a valuable teaching tool for the role that science can play in formulating good policy, while also providing an opportunity to review a few basic concepts in nuclear physics.

     

    November 29, 2018

    Gerald Gabrielese, Northwestern University

    Stringent Tabletop Tests of the Standard Model:  A Tale of the Electron's Electric and Magnetic Dipole Moments

    Abstract: The standard model's most precise prediction -- of the size of the electron magnetic moment -- is tested using a single electron suspended by itself for months at a time in a tabletop-sized measurement.  Also, a new measurement of the electrons' other moment -- its electric dipole moment - was just completed in a very different tabletop measurement. The standard model and proposed alternatives/additions differ sharply in their predictions of the size of this moment.

     

    December 6, 2018

    Francis Halzen, Wisconsin IceCube Particle Astrophysics Center and Department of Physics, University of Wisconsin–Madison

    IceCube: Opening a New Window on the Universe from the South Pole.

    Abstract: The IceCube project has transformed a cubic kilometer of natural Antarctic ice into a neutrino detector. The instrument detects more than 100,000 neutrinos per year in the GeV to PeV energy range. Among those, we have isolated a flux of high-energy neutrinos of cosmic origin. We will explore the IceCube telescope and the significance of the discovery of cosmic neutrinos. We recently identified their first source: alerted by IceCube on September 22, 2017, several astronomical telescopes pinpointed a flaring galaxy powered by an active supermassive black hole, as the source of a cosmic neutrino with an energy of 290 TeV. Most importantly, the large cosmic neutrino flux observed implies that the Universe's energy density in high-energy neutrinos is close to that in gamma rays, suggesting that the sources are connected and that a multitude of astronomical objects await discovery.

  • Fall 2017 and prior