Rutgers Department of Physics and Astronomy
Colloquia Are Held In The Physics Lecture Hall
At 4:45 P.M. On Wednesday Afternoons
Tea served 4.30pm-4.45pm All welcome.
Fall 2015 Schedule
Fascinating photo-physics of functional organic surfaces and interfaces
Small-molecule organic semiconductors form the basis of the field of organic optoelectronics. In order to better understand the intrinsic photo-physical and transport phenomena in this important class of materials, it is necessary to study samples of very high structural order and chemical purity. Such materials exist in the form of molecular single crystals that can be used for fabrication of high-performance prototype devices, such as field-effect transistors, photo-conductors and photo-voltaic cells, in which intrinsic properties of organic semiconductors can be investigated without parasitic effects of disorder. This talk will overview some of the main achievements in the area of organic single-crystal devices, present resent progress and discuss novel methods of surface functionalization that result in an extremely low-noise charge transport regime at the surface of molecular crystals, leading to an observation of unprecedentedly clean and quiet (low-noise) Hall effect. In addition, very interesting non-linear effects in photoconductivity, originating from long-range exciton diffusion and multi-particle interactions, will be discussed.
Strange metals and black holes
Strange metals are conducting states of quantum matter without any quasiparticle excitations. The copper-based high temperature superconductors display a strange metal at temperatures above the critical temperature, T_c, for superconductivity, and at electron densities where T_c is maximal. I will (i) describe a solvable model of a strange metal whose properties match quantitatively with those of charged black holes; (ii) outline a general framework for computing observable properties of strange metals, drawing upon numerous theoretical methods, including the black hole mapping; (iii) describe a recent experiment in graphene, in which theory is compared with a (slightly less) strange metal.
|16-Sept|| Eva Halkiadakis
Exploring the Energy Frontier at the Large Hadron Collider
The Large Hadron Collider (LHC) at the CERN laboratory is the world’s most powerful particle accelerator. The start of the proton collider program at the LHC brought the dawn of the exploration of a new energy frontier. The LHC has had a successful and highly productive Run 1 (2010-2012), colliding protons with a center-of-mass energy up to 8 TeV, and in 2012 the observation of a new Higgs-like boson was announced to the world by the CMS and ATLAS collaborations. This year marks the beginning of Run 2 of the LHC and we entered a new era of even higher proton collisions at 13 TeV. I will give an overview of the extensive program at the LHC to search for physics beyond the Standard Model, with a special focus on searches for Supersymmetry, a theory that predicts a symmetry between matter and forces and provides a promising candidate for dark matter. I will also present the status of the LHC and the first results from the CMS experiment using the latest 13 TeV data in Run 2, further exploring uncharted territory at the energy frontier.
|23-Sept|| Francis Halzen
IceCube and the Discovery of High-Energy Cosmic Neutrinos
The IceCube project has transformed one 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 recently isolated a flux of high-energy cosmic neutrinos. I will discuss the instrument, the analysis of the data, and the significance of the discovery of cosmic neutrinos. The high cosmic neutrino flux observed indicates that a significant fraction of the radiation in the non-thermal universe, powered by compact objects from neutron stars to supermassive black holes, is generated by proton accelerators.
The Origin of Spirals in Galaxies
Spiral galaxies have been observed for over 150 years, but so far no satisfactory explanation for the origin of their beautiful spiral patterns has been provided. Most theorists expect them to be a consequence of gravitationally-driven, collective oscillations of the stellar system, which is supported by the evidence that recurrent spiral patterns appear spontaneously in large numerical simulations. While the physics of small-amplitude spiral wave packets is well-established, most previous attempts to calculate modes have foundered because spiral waves are strongly damped at resonances in smooth stellar disks. I demonstrate that the non-linear scattering of stars by one spiral wave creates impedance changes in the stellar disk from which new waves can reflect, allowing true standing waves to be established and leading to a recurrent cycle of spiral instabilities.
Baryons and the Borromeo
The kernels in the tangible matter of our everyday experience are composed of light quarks. At least, they are light classically; but they don't remain light. Dynamical effects - novel forces - within the Standard Model of Particle Physics change the light quarks in remarkable ways, so that in some configurations they appear nearly massless but in others possess masses on the scale of light nuclei. Modern experiment and theory are exposing the mechanisms responsible for these remarkable transformations. The prize is $1-million, if the emerging sketches can be combined into an accurate picture of confinement, the eternal imprisonment of quarks, which is such a singular feature of the Standard Model. Looming larger amongst the emerging ideas is a perspective that leads to a Borromean picture of the proton and its excited states; and along with this view comes a marked change in how one might understand the Standard Model's ground-state or "vacuum".
Bulk Locality and Quantum Error Correction in AdS/CFT
The AdS/CFT correspondence has given us a non-perturbative description of quantum gravity in asymptotically anti de Sitter space, as a quantum field theory (without gravity) living in a lower number of dimensions. This proposal has passed many tests, but the emergence of bulk locality in the new radial direction has remained somewhat mysterious. In this talk I will discuss recent work relating this phenomenon to the theory of quantum error correcting codes, which was introduced to solve the seemingly unrelated problem of protecting a quantum computer from decoherence. We will see that there are interesting puzzles in AdS/CFT that are naturally resolved in this language, which we will also see gives a sharp meaning to speculations over the past decade relating boundary entanglement to the emergence of bulk geometry. I will illustrate these ideas using an explicitly soluble model of AdS/CFT, constructed using tensor networks.
CANCELLED: Robbins Lecture Self-calibration, systematic errors, and exoplanet discovery
Finding exoplanets is hard: They appear as extremely tiny signals in any data set. Intrinsic stellar variability and variability induced by the spacecraft (or telescope or atmosphere) are both larger (in almost all data sets) than the exoplanet signals of interest. The best information about these sources of variability comes from the scientific data themselves; that is, the most sensitive searches for exoplanets are self-calibrated. I use Kepler and K2 data to illustrate these points, showing a set of discoveries in the K2 mission, where the spacecraft-induced variability is larger than most exoplanet signals by more than an order of magnitude. (Come prepared to suffer through some linear algebra.)
|11-Nov|| Collin Broholm
Strange Magnetism Exposed by Neutron Scattering
A radically different form of magnetism defined by quantum entanglement is explored using neutron scattering. Starting from illustrative one-dimensional examples, I discuss recent experiments that probe magnetic excitations in two and three-dimensional frustrated quantum magnets. In analogy with atomic positions in superfluid 4He, atomic scale magnetic dipoles in these materials exist in a state of quantum superposition near the absolute zero temperature. While there is no static magnetic order to distinguish such materials they host exotic emergent quasi-particles that scatter neutrons. The potential relevance of the quantum spin liquid to high temperature superconductivity shall be illustrated through our recent quantitative and spatially resolved measurements of the superconducting condensation energy in Fe_(1+y)Se_xTe_(1-x).
|18-Nov|| Abhay Deshpande
| Understanding the glue that binds us all: the science of the future Electron Ion Collider
We know enough about the fundamental properties of quarks, gluons (collectively called: patrons) and their interactions to be sure that QCD is the correct theory of Strong Interactions. However, when a large number of partons are put together, their collective behavior is often surprising i.e. un-understood. Gluons seem to play a central role in most of these instances. For example, despite forty years of dedicated experimental efforts around the world (CERN, SLAC, DESY, BNL & JLab) and the associated theoretical development in this field, we still do not understand how the nucleon’s spin, a fundamental property of the nucleon, comes about from the collection of its constituents and their interactions. We do not yet fully understand the confinement of patrons in colorless hadrons. Do patron’s angular momentum and gluon’s helicity contributions have something to do with it?. — We do not know yet. On the other hand, when nucleons or nuclei are accelerated to high energies, and explored with a high energy probe, a new state of universal gluon dominated matter is predicted based on experimental evidence from the high energy e-p collider (HERA) at DESY, and nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). If such a state of universal gluonic matter (the Color Glass Condensate) exists, it would be fundamentally important to explore and understand its properties. A high-energy high-luminosity electron-ion collider (EIC) with polarized beams and variable center-of-mass energy will be an ideal machine to explore these emergent phenomena and address the most compelling and yet unresolved questions in QCD. I will review the science highlights that motivate this collider and present the prospects of its realization.
| Theory opportunities in nuclear science at the limits of stability
The ultimate goal for nuclear theory is to develop a predictive understanding of nuclei and their interactions grounded in QCD. In addressing this challenge, nuclei at the limits of stability play a crucial role, in that they unveil detailed features of the underlying force. In addition to the intersection of nuclear physics, and astrophysics and cosmology, our fermionic systems exhibit emergent phenomena that are present in other complex systems studied by quantum chemists, atomic, molecular, and condensed-matter physicists, and materials scientists. An overview of the overarching questions our community is addressing will be presented, highlighting the theoretical opportunities that lie ahead. Also, a few concrete examples of my own research in reaction theory will be discussed, demonstrating the importance of coupling theory and experiment for the advancement of the field.
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