Past Events

  • Condensed Matter seminar: "Phonon superconductivity and Landau levels of the twisted bilayer graphene"

    David Rittenhouse Laboratory, A4

    Biao Lian, Princeton University

    The twisted bilayer graphene (TBG) near the magic twist angle 1.05 degrees is known to have extremely flat electron bands, and exhibits both superconductivity and correlated insulating phases. In the first part, we show that the electron-phonon coupling is enhanced by the twist structure, which is strong enough to induce conventional BCS superconductivity with a critical temperature around 1K. We further predict the possible BCS superconductivity at other twist angles and in higher electron bands. In the second part, we explore the Landau levels and Hofstadter butterfly of the TBG.

  • Condensed Matter seminar: "Quantum Many-Body Physics Beyond Ground States"

    David Rittenhouse Laboratory, A4

    Thomas Iadecola, University of Maryland

    Recently a set of traditional assumptions in quantum condensed matter theory has been upended by the realization that many-body systems can host stable quantum phenomena at infinite temperature.  I will discuss recent work suggesting that there is a much richer landscape of such phenomena than has so far been appreciated.  First, I will show how strongly disordered quantum many-body systems can spontaneously segregate into delocalized and localized degrees of freedom, leading to a so-called "mobility emulsion." Second, I will discuss how symmetries in otherwise generic sys

  • Astronomy seminar: "Detecting IGM structures in the very early Universe: Status, challenges, and new approaches"

    David Rittenhouse Laboratory, A2

    Nithya Thyagarajan (NRAO)

    Direct detection of evolving neutral Hydrogen structures from the Cosmic Dawn and Reionization Epochs (EoR) will reveal the nature of the first stars and galaxies as well as complete our understanding of a significant evolutionary phase of the Universe. In contrast with some recent exciting results from the EDGES experiment, detection of IGM structures using redshifted 21 cm by many experiments such as the MWA, LOFAR, and PAPER that commenced in the last decade has remained elusive.

  • High Energy Theory seminar: "Higgs Couplings at High Scales"

    David Rittenhouse Laboratory, A4

    Tao Han, University of Pittsburgh

    Experiments at the LHC have been improving the measurements of the Higgs boson properties, and the searches for new physics are being actively conducted. In the absence of deviations from the Standard Model thus far, it would be prudent to seek for other complementary strategies in the experiments at the energy frontier. For this purpose, we propose to study the Higgs couplings at high energy scales, relevant to addressing the naturalness problem in the Higgs sector. We focus on the energy scale-dependence of the off-shell Higgs propagation, and of the top quark Yukawa coupling.

  • Condensed Matter seminar: "Excitons in Flatland: Exploring and Manipulating Many-body Effects on the Optical Excitations in Quasi-2D Materials"

    David Rittenhouse Laboratory, A4

    Diana Qiu, Lawrence Berkeley Laboratory

    Since the isolation of graphene in 2004, atomically-thin quasi-two-dimensional (quasi-2D) materials have proven to be an exciting platform for both applications in novel devices and exploring fundamental phenomena arising in low dimensions. This interesting low-dimensional behavior is a consequence of the combined effects of quantum confinement and stronger electron-electron correlations due to reduced screening.

  • Experimental Particle Physics Seminar: "Muon Radiography at the Los Alamos National Laboratory and Brunelleschi's dome in Florence"

    David Rittenhouse Laboratory, A8

    Elena Guardincerri, LANL

  • Condensed Matter seminar: "Strange quantum matter: Fermi surfaces sans Fermi liquids"

    David Rittenhouse Laboratory, A4

    Debanjan Chowdhury, Massachusetts Institute of Technology

    The concept of electronic quasiparticles, as introduced by Landau, is one of the cornerstones of the theory of quantum many-body systems. However, a growing number of recent experiments in strongly correlated quantum materials have forced us to confront the existence of quantum matter for which the concept of electronic quasiparticles does not apply. In the first part of this talk, I will consider the physics of an electrical insulator, where recent experiments have suggested the existence of gapless neutral fermionic excitations.

  • Astronomy seminar: "Dark Matter in Disequilibrium"

    David Rittenhouse Laboratory, A2

    Mariangela Lisanti, Princeton University

    The Gaia mission is in the process of mapping nearly 1% of the Milky Way’s stars. This data set is unprecedented and provides a unique view into the formation history of our Galaxy and its associated dark matter halo. I will review results based on the most recent Gaia data release, which demonstrate that the inner Galaxy is dominated by the stellar remnants of a single massive satellite galaxy that merged with the Milky Way early on.

  • High Energy Theory seminar: "Holographic Entropy Cone with Time Dependence"

    David Rittenhouse Laboratory, 2N36

    Bartek Czech, Tsinghua University

    In the AdS/CFT correspondence, if a CFT state is dual to a semiclassical spacetime, its entanglement entropies (minimal surface areas) must obey certain inequalities. The best-known examples are the strong subadditivity of entanglement entropy (SSA) and the monogamy of mutual information (MMI). Together, such inequalities define the so-called holographic entropy cone.

  • Condensed Matter seminar: "Exploring the Landscape of Complex Quantum States: From New Phases of Matter to Robust Schemes for Quantum Computation"

    David Rittenhouse Laboratory, A4

    Ksheerasagar "Sagar" Vijay, Harvard University

    We present recent advances in our understanding of (i) exotic quantum phases of matter in three dimensions, and (ii) robust mechanisms for storing and processing quantum information, that have been enabled by new techniques to study highly-entangled quantum states.  First, we introduce fundamentally new kinds of gapped quantum phases in three spatial dimensions, which are characterized by the presence of point-like excitations that are strictly immobile at zero temperature, and by degenerate ground-states that are locally indistinguishable.