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Colloquia & Seminars
  • JQI Seminar
    Speaker:Bruno Laburthe-Tolra, Laboratoire de Physique des Lasers – Paris 13 University & CNRS – UMR 7538

    Title:Magnetic properties of chromium dipolar condensates

    Abstract: In this seminar, I will describe an experiment where magnetic atoms in different sites of a 3D optical lattice undergo spin-exchange processes due to long-range dipole-dipole interactions.
    A Bose-Einstein condensate of Chromium atoms is loaded into deep 3D optical lattices. Due to their large magnetic dipole moment, Chromium atoms interact at long distance via dipole-dipole interactions. These interactions provide intersite spin-spin interactions without relying on super-exchange energies, which constitutes a great interest for the study of spin lattice models. In our experiment, we observe a non-equilibrium spinor dynamics resulting from inter-site Heisenberg-like spin-spin interactions provided by non-local dipole-dipole interactions. Our experiment thus reveals the interest of chromium lattice gases for the study of quantum magnetism of high-spin systems.
    I will also show that the anisotropy of dipolar interactions introduces the possibility of magnetization-changing collisions. In a lattice, these collisions may resonantly happen when the energy released in a dipolar relaxation event (the Larmor energy, tuned by the magnetic field) matches the energy for band excitation. Dipolar interactions thus introduce an intrinsic non-linear spin-orbit coupling which may qualitatively modify the study of quantum magnetism.

    Host: Trey Porto
    When: Mon, April 21, 2014 - 11:00am
    Where: CSS 2400
  • Nuclear Physics Seminar
    Title: Unearthing excited hadron resonances in lattice QCD

    Speaker: Colin Morningstar, Carnegie Mellon

    Abstract: Recent advances in computational techniques in lattice QCD have enabled unprecedented access for theoretical studies to QCD excited states. First results of stationary-state levels in several symmetry sectors using very large sets of both single-meson and two-meson operators are presented. Level identification using probe operators is discussed.
    When: Mon, April 21, 2014 - 1:30pm
    Where: PSC 3150
  • EPT Seminar
    Title: Non-thermal Dark Matter: Prospects and Challenges

    Speaker: Kuver Sinha, Syracuse

    Abstract: Given the ever-shrinking parameter space for dark matter that satisfies the relic density through thermal freeze-out, it is interesting to explore non-thermal histories for dark matter. I discuss constraints from indirect and direct detection, dark radiation bounds, and minimal conditions that need to be satisfied for a non-thermal scenario to work. I also discuss the decay of stabilized moduli in string compactifications and their viability in giving rise to a non-thermal scenario.
    When: Mon, April 21, 2014 - 3:00pm
    Where: PSC 3150
  • Biophysics Seminar
    Speaker Name: Sergey Bezrukov

    Speaker Institution : NIH

    Title : Transport under strong confinement: Counter-intuitive analytical results and supporting experiments with beta-barrel channel
    When: Mon, April 21, 2014 - 4:00pm
    Where: 0112 Chemistry Building
  • Space and Cosmic Ray Physics Seminar
    Speaker Name: Nat Gopalswamy

    Speaker Institution : Solar Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771

    Title: Space Weather Consequences of the Weak Solar Activity Cycle 24

    Abstract: The two main space weather consequences of solar activity are large solar energetic particle (SEP) events and major geomagnetic storms. The weak solar activity during solar cycle 24 seems to affect the SEP production in a peculiar way: the number of large SEP events is similar to that in cycle 23, but the particles are not accelerated to high energies, as evidenced by the dearth of ground level enhancement (GLE) events. The frequency and intensity of large geomagnetic storms are also at a historical low during solar cycle 24. Even though the Sun is in its maximum phase, there have been only a dozen major storms (Dst ≤ -100 nT) in cycle 24 so far, compared to 40 storms during the first 5 years of cycle 23. The storm intensity never exceeded 140 nT, whereas there were 9 storms in cycle 23 with Dst ≤ -200 nT (one of the storms had Dst ~ -301 nT). Both large SEP events and major geomagnetic storms are caused by energetic CMEs. When we examined the properties of the associated CMEs, we found that the average speed of SEP-producing CMEs is larger than that in cycle 23. Furthermore, all SEP-producing CMEs of cycle 24 are halos, compared to about 70% in cycle 23. The average speed of storm-producing CMEs was about 40% higher than that in the first half of cycle 23. The fraction of halo CMEs is also about 20% higher. In other words, cycle-24 CMEs seem to require more energy to produce similar or weaker space weather events. These observations indicate that there is something fundamentally different about cycle-24: CMEs seem to expand anomalously owing to the reduced heliospheric pressure. We suggest that such expansion dilutes the magnetic content of CMEs, thus resulting in weaker interaction with the magnetosphere. Another consequence of the weak cycle is the reduced magnetic field in the heliosphere, which might have reduced the efficiency of particle acceleration.

    Notes: Coffee, Tea & Cookies 4:15-4:30 PM
    When: Mon, April 21, 2014 - 4:30pm
    Where: Computer & Space Science Building, Room 2400
  • CMTC Seminar
    Speaker: Amir Yacoby (Harvard)

    Title: Induced Superconductivity in the Quantum Spin Hall Edge

    Abstract: Topological insulators are a newly discovered phase of matter characterized by a gapped bulk surrounded by novel conducting boundary states. Since their theoretical discovery, these materials have encouraged intense efforts to study their properties and capabilities. Among the most striking results of this activity are proposals to engineer a new variety of superconductor at the surfaces of topological insulators. These topological superconductors would be capable of supporting localized Majorana fermions, particles whose braiding properties have been proposed as the basis of a fault-tolerant quantum computer. Despite the clear theoretical motivation, a conclusive realization of topological superconductivity remains an outstanding experimental goal. Here we present measurements of superconductivity induced in two-dimensional HgTe/HgCdTe quantum wells, a material which becomes a quantum spin Hall insulator when the well width exceeds dC = 6:3 nm. In wells that are 7.5 nm wide, we find that supercurrents are confined to the one-dimensional sample edges as the bulk density is depleted. However, when the well width is decreased to 4.5 nm the edge supercurrents cannot be distinguished from those in the bulk. These results provide evidence for superconductivity induced in the helical edges of the quantum spin Hall effect, a promising step toward the demonstration of one-dimensional topological superconductivity. Our results also provide a direct measurement of the widths of these edge channels, which range from 180 nm to 408 nm.

    Host: Kostyantyn Kechedzhi

    When: Tue, April 22, 2014 - 1:00pm
    Where: 2205 Physics Building
  • Informal Statistical Physics Seminar
    Speaker Name: Professor David Levermore

    Speaker Institution : University of Maryland, College Park

    Title : Modeling Portfolios that Contain Risky Assets.
    When: Tue, April 22, 2014 - 1:15pm
    Where: Room 1116, IPST Building, Bldg 85
  • Physics Colloquium
    Speaker Name: Andrew Steiner

    Speaker Institution: University of Washington

    Title: How Neutron Star Observations Constrain the Nucleon-Nucleon Interaction

    Abstract: Recent neutron star observations have had a drastic impact on both
    neutron star models and nuclear physics. The measurement of two 2 solar mass neutron stars has ruled out most of the previously accepted theoretical models. As of 6 years ago, neutron star radii were commonly accepted to be between 8 and 15 km. Recent neutron star radius measurements suggest a smaller range, between 10 and 13 km. Neutron stars are the only laboratory in which we can study cold, dense, and strongly-interacting matter, and thus all of these observations have important implications for nuclear physics. Neutron
    star radius measurements constrain models of three-neutron forces and the so-called "nuclear symmetry energy", both of which are not well-constrained by data from nuclei accessible in the laboratory. I will show how these constraints arise from the observational data and demonstrate that there is a growing concordance with advances in quantum Monte Carlo simulations of pure neutron matter and chiral effective theory.
    When: Tue, April 22, 2014 - 4:00pm
    Where: PHYS 1412
  • Gravity Theory Seminar *New location*
    Title: Stellar Tidal Disruption: the Role of General Relativity

    Speaker: Nicholas Stone, Columbia

    Abstract: In tidal disruption events (TDEs), stars passing too close to supermassive black holes (SMBHs) are violently torn apart. I will discuss several recent findings about the light curves of these events, including the role of orbital pericenter, ways in which the spin of the SMBH can be imprinted into TDE light curves, and possible emission of high frequency gravitational waves. I will also discuss an ongoing project focused on how highly eccentric debris streams from a TDE can circularize into a luminous accretion disk. It appears likely that the circularization process is mediated by general relativistic effects: circularization is aided by apsidal precession and hindered by nodal precession due to Lense-Thirring torques. The spin of the SMBH may therefore be encoded in the debris circularization timescale.
    When: Wed, April 23, 2014 - 1:30pm
    Where: PSC 1136
  • JQI Special Seminar
    Speaker Name: Russell Bisset

    Speaker Institution: Los Alamos National Laboratory

    Abstract: An important feature of the alkali atoms typically used for weakly interacting Bose-Einstein condensates is that their interactions are short-ranged and can be well-approximated by a contact interaction. In 2005 the Stuttgart group obtained the first BEC of chromium, a system with an important new feature: Ground state chromium atoms have a large magnetic dipole moment leading to an appreciable dipole-dipole interaction. These interactions are long-ranged and anisotropic, and a range of new physics is expected to arise. Recently, there were a number of breakthroughs with the condensation of dipolar erbium and dysprosium atoms. There has also been considerable progress towards the production of quantum degenerate polar molecules with large electric dipoles.

    In this talk I will review some of the interesting experimental and theoretical work on dipolar systems. Of particular interest is that, in the pancake trap, a momentum dependence of the interaction is predicted which may even lead to a new kind of (weakly interacting) roton. This roton has not been observed experimentally and I will discuss our work that predicts its dramatic manifestation in the density fluctuations. These effects should be observable in current experiments with recent advances in imaging (e.g. the quantum gas microscope).

    Host: Ryan Wilson
    When: Wed, April 23, 2014 - 2:00pm
    Where: CSS 2115
  • Plasma Physics Seminar
    Speaker Name: Dr. Robert Kaita

    Speaker Institution : Princeton Plasma Physics Laboratory

    Title : Addressing the First Wall Challenge for Magnetic Confinement Fusion in the National Spherical Torus-Upgrade
    When: Wed, April 23, 2014 - 4:00pm
    Where: Room 1207, Energy Research Facility
  • Applied Dynamics Seminar
    Speaker Name: Julian Candia

    Speaker Institution : UMD

    Title : Unbiased Learning from Big Data: Multidimensional Approaches for Data-Driven Biomedical Research
    When: Thu, April 24, 2014 - 12:30pm
    Where: IREAP Large Conference Room (ERF 1207)
  • Refreshments for CNAM Colloquium

    When: Thu, April 24, 2014 - 1:30pm
    Where: Phys Room 1305F
  • Nuclear Physics Seminar
    Title: Electromagnetic form factors of the octet baryons from lattice QCD

    Speaker: Phiala Shanahan, Adelaide

    Abstract: I will present the results of recent lattice simulations of the electromagnetic form factors of the octet baryons from the CSSM/QCDSF/UKQCD collaborations. The focus will be on the analysis of those results using techniques to approach the infinite volume limit and the physical pseudoscalar masses at non-zero momentum transfer. The extrapolated proton and neutron form factors are found to be in excellent agreement with those extracted from experiment. Given the success of these calculations, I will describe how the strange electromagnetic form factors may be estimated from these results under the same assumption of charge symmetry used in experimental determinations of those quantities. Motivated by the necessity of that assumption, I will explore a method for determining the size of charge symmetry breaking effects using the same lattice results discussed previously.
    When: Thu, April 24, 2014 - 1:30pm
    Where: 3150 PSC
  • CNAM Colloquium
    Speaker: Jonathan Denlinger, Advanced Light Source, Lawrence Berkeley
    National Laboratory

    Title: Thermal gap destabilization and the fate of topologically protected surface states in the mixed valent insulator SmB6

    Abstract: The paradigm mixed-valent insulator SmB_6 has experienced recent renewed
    interest coming from the prediction of the existence of topological surface states arising from the inversion of f and d-bands at the X-point, and from transport measurements giving evidence for surface conductivity at low temperatures. The existence of such surface states
    would provide an explanation for a 30 year puzzle as to the origin of “in-gap” states causing a metallic resistivity saturation below 4K. In this work angle-resolved photoemission on cleaved <100> surfaces provides the first experimental view of the X-point conduction band, the T-dependent destabilization of the many-body hybridization gap and the intimately connected fate of the topologically protected X-point surface
    states that reside in the gap [1]. The T-dependent evolution of the bulk states compares very well with bulk transport properties and the qualitative implications of DFT+DMFT calculations.But presently there is no such theory for the surface states.Spatial variations of the surface state properties and the extent of their robustness on inhomogeneous
    cleaved surfaces arising from large charge polarity differences between Sm- and B-terminated regions is also presented [2].

    [1] J.D. Denlinger, et al., /arXiv/:1336.6637;
    [2] J.D. Denlinger, et al. /arXiv/:1336:6636.

    Hosts: J. Paglione & N. Butch
    When: Thu, April 24, 2014 - 2:00pm
    Where: Phys Room 1201
  • Materials Science and Engineering Seminar
    Speaker Name: Eckhard Quandt

    Speaker Institution : Institute for Materials Science, Christian-Albrechts-Universität, Kiel, Germany

    Title : Superelastic TiNi Thin Film Medical Implants

    Abstract : Shape memory alloys based on binary equiatomic TiNi exhibits superelastic properties with superelastic strains larger than 8%, tensile strengths up to 1400 MPa, and breaking elongations up to 60%. Additionally, the material is known to reveal an excellent biocompatibility. Both features result in a high attractiveness for its use for medical implants and devices, as, e.g., for example stents. For further miniaturization of medical implant, e.g., for neurostents, thin film technology has gained increasing interest in comparison to traditional bulk fabrication routes.

    This presentation will cover the fabrication of micropatterned freestanding TiNi thin films, will discuss the mechanical and the fatigue properties in comparison to traditional bulk TiNi, will show the new possible functionalities of thin film stents and will present a method to fabricate NiTi thin film leaflets for transcatheter aortic valve replacements.

    Funding by the DFG (German Science Foundation) is gratefully acknowledged.
    When: Fri, April 25, 2014 - 1:00pm
    Where: Room 2110 Chemical & Nuclear Engineering Building
  • JQI Seminar
    Speaker Name: Vanderlei Bagnato

    Speaker Institution: Instituo de Fisica de Sao Carlos - University of S. Paulo

    Abstract: In this seminar we shall describe the observation of superfluid turbulence
    in an atomic trapped sample of Rb. Description of excitation, final side
    effect, and hydrodynamic properties will be presented. Simulations that
    justify the experimental observations will be presented. In a second part
    of the seminar, the possibility to describe the thermodynamics of a trapped
    superfluid using global ( in instead of local) variables will be discussed.
    Measurement of heat capacity, compressibility and the evidences of
    complementarities between pressure and volume will be discussed.

    Host: Luis Orozco
    When: Mon, April 28, 2014 - 11:00am
    Where: CSS 2400
  • Nuclear Physics Seminar
    Title: TBA

    Speaker: Shailesh Chandrasekharan, Duke

    Abstract: TBA
    When: Mon, April 28, 2014 - 1:30pm
    Where: PSC 3150
  • Space and Cosmic Ray Physics Seminar
    Speaker Name: Greg Sullivan

    Speaker Institution : University of Maryland, Physics

    Title: TBA

    Notes: Tea and Cookies 4:15-4:30 pm
    When: Mon, April 28, 2014 - 4:30pm
    Where: CSS 2400
  • Biophysics - No Seminar Held Today

    When: Sun, April 27, 2014 - 8:00pm

Department of Physics

University of Maryland
College Park, MD 20742-4111
Phone: 301.405.3401
Fax: 301.314.9525