condensed matter events

CONDENSED MATTER SEMINARS

Thursdays at 4:00 pm in B&H 190

FALL 2009

SEPTEMBER

Thursday, September 10, 2009 at 4 pm B&H 190

             (This talk is being rescheduled!)
             Dr. Qiang Li
             Brookhaven National Laboratory

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         Host: Sean Ling

Thursday, September 17, 2009 at 4 pm B&H 190

            Dr. Brian Maranville
            NIST, Gaithersburg, Maryland

            “Offspecular Reflectometry at the NIST Center for Neutron Research”

Abstract: Neutron reflectometry and Small-Angle Neutron Scattering (SANS) are well-established techniques for the characterization of the nuclear and magnetic structure of materials (in thin-film, planar or otherwise 2-dimensional form). These measurements complement X-ray scattering measurements with similar geometries, while offering the unique advantages of neutrons as a probe: large penetration depths, strong magnetic interactions, and strong nuclear scattering from relatively weak x-ray scatterers like Hydrogen. In the specular measurement geometry only the scattering in one dimension, along the surface normal of a planar sample. In small-angle scattering geometry, the probe wave is normal to the surface and the observed scattering is all perpendicular to the sample plane. At the NIST Center for Neutron Research (NCNR), we are actively developing an offspecular reflectometry instrument (to be called MAGIK). This instrument is designed to fill in the gaps between specular reflectometry and SANS, offering the high intensity and high in-plane resolution of the reflectometry geometry (with an option for resolving full 3-dimensional scattering.) Analysis of the data is complicated by the fact that we are looking at scattering from near-glancing-angle neutrons, and optical (continuum approximation) effects are evident in the scattering. An effort to model the data using a Distorted-Wave Born Approximation is underway. Several systems have already been investigated, including organic thin-film solar cell materials, self-assembled diblock-copolymer lamellar arrays, and patterned magnetoelectronic elements, with results presented.

Host: Sean Ling

        Thursday, September 24, 2009 at 4 pm B&H 190

Prof. Chung-Hou Chung
Yale University

“Electronic Transport Through Quantum Dots in the Kondo Regime”

Abstract: Transport of electrons at low temperatures in nano-devices such as semiconductor quantum dots has led to many fascinating phenomena in recent years. In these devices electrons are confined in a very small region at the nano-scale with strong electron-electron repulsion, leading to strong suppression of charge fluctuations, so called “Coulomg Blockade”. However, if the quantum dot contains odd number of electrons, the spins of conduction electrons tend to couple antiferromagnetically to those in the quantum dots, so called the “Kondo effect”. This leads to enhancement of zero-bias conductance at low temperatures. In this talk, I will present a few interesting examples of my recent works on quantum transport in quantum dots associated with Kondo effect.
In this talk, I will focus on the systems where Kondo effect competes with additional interactions in the systems which couple to the quantum dot. Examples are the antiferromagnetically coupled double-quantum-dot-system and a dissipative quantum dot coupled to a noisy environment induced by quantum charge fluctuations in the setup. When there is more than one competing quantum ground states, interesting “quantum phase transitions” often occur. These are the continuous phase transitions at zero temperature between one quantum ground state to another, which give rise to many unconventional transport properties at low temperatures near the “quantum critical point". Moreover, there is a growing interest in nonequilibrium transport through a Kondo dot near the quantum phase transition when an external bias voltage is imposed on the dot. I will discuss some of the new results on both equilibrium and nonequilibrium charge transports near the quantum phase transition of the Kondo dot systems. Due to high tenability of these nano-devices, one can address fundamentally important issues in both Condensed Matter and Mesoscopic physics.

Host: Brad Marston

OCTOBER

Thursday, October 1, 2009 at 4 pm B&H 190

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        Thursday, October 8, 2009 at 4 pm B&H 190

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        Thursday, October 15, 2009 at 4 pm B&H 190

               Prof. Christoph Naumann
               Indiana University-Purdue University Indianapolis

“Polymer-Tethered Lipid Bilayers as Complex Model Membrane Platforms and Viscous Cell Substrates”

Abstract: Polymer-tethered lipid bilayers comprised of phospholipids and lipopolymers represent attractive mimetics of cellular membranes. The first part of the talk will present a set of biophysical studies, which highlight the ability to tune and characterize lipid organization and dynamics in these supramolecular assemblies. They include: (1) the complex formation between GPI-anchored urokinase plasminogen activator receptors (uPAR) and membrane-spanning integrins (αvβ3 and α5β1); (2) the transbilayer coupling of raft-mimicking lipid domains and the impact of physisorbed actin-filaments on these functional domains; and (3) the regulation of obstacle-induced obstructed lipid/protein diffusion by polymer-tethered lipids. In the second part of the talk, polymer-tethered lipid membranes will be employed as biomembrane-mimicking cell substrates. Previous experiments on polymer gels of adjustable elasticity have shown that cells probe the environment by an adaptive process of focal contact assembly/disassembly that crucially affects cell adhesion and morphology. Here we present results from neurons and fibroblasts, which show that the adhesion and morphology of cells can be similarly controlled through the adjustment of substrate viscosity in planar polymer-tethered membranes containing laminin-functionalized cell linkers. In this case, substrate viscosity is adjusted either by the molar concentration of lipopolymers in a single polymer-tethered lipid bilayer or by the number of bilayers in a stack of multiple, polymer-interconnected lipid bilayers causing a distinct degree of frictional coupling between adsorbed cell and underlying solid substrate. Our experiments illustrate that the dynamic assembly/disassembly of linkers makes the described cell substrate a powerful tool for the study of dynamic, mechano-regulated cell linkage.

Host: Jay Tang

Thursday, October 22, 2009 at 4 pm B&H 190

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    Thursday, October 29, 2009 at 4 pm B&H 190

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NOVEMBER

       Thursday, November 5, 2009 at 4 pm B&H 190

                Prof. Chris Henley
                Cornell University

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                    Host: Jay Tang

        Thursday, November 12, 2009 at 4 pm B&H 190

               Dr. Peter B. Weichman
               BAE Systems

“Dirty Bosons: Twenty Years Later”

Abstract: I will present a somewhat personal review of the problem of superfluidity and quantum criticality in regular and disordered interacting Bose systems, illustrated with experiments on He-4 adsorbed in porous Vycor glass, on thin film superconductors, and, most recently, in systems of magnetically trapped atomic vapors in random optical potentials. I will discuss the general features and important symmetries that are exhibited in different parts of the phase diagram, and that govern the different possible types of critical behavior. A number of exact results for various insulating phase boundaries, which may be used to constrain the results of numerical simulations, can be derived using large rare region type arguments. The nature of the insulator-superfluid transition is explored through general scaling arguments, exact model calculations in one dimension, numerical results in two dimensions, and approximate renormalization group results in higher dimensions.

Host: Brad Marston

Thursday, November 19, 2009 at 4 pm B&H 190

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         Thursday, November 26, 2009 at 4 pm B&H 190

              Thanksgiving Holiday

DECEMBER

Thursday, December 3, 2009 at 4 pm B&H 190

                Prof. Michael Shelley
                Courant Institute, NYU

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Host: K. Breuer

Tuesday, December 10, 2009 at 4 pm B&H 190

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     Thursday, December 17, 2008 at 4 pm B&H 190

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SPRING 2010

JANUARY

Thursday, January 28, 2009 at 4 pm B&H 190

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FEBRUARY

    Thursday, February 4 2009 at 4 pm B&H 190


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     Thursday, February 11, 2009 at 4 pm B&H 190

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    Thursday, February 18, 2009 at 4 pm B&H 190

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Thursday, February 25, 2009 at 4 pm B&H 190

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MARCH

Thursday, March 4, 2009 at 4 pm B&H 190

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Thursday, March 11, 2009 at 4 pm B&H 190

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Thursday, March 18, 2009 at 4 pm B&H 190

APS March Meeting

Thursday, March 25, 2009 at 4 pm B&H 190

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APRIL

    Thursday, April 1, 2009 at 4 pm B&H 190

        Spring Break

    Thursday, April 8, 2009 at 4 pm B&H 190

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    Thursday, April 15, 2009 at 4 pm B&H 190

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Thursday, April 22, 2009 at 4 pm B&H 190

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Thursday, April 29, 2009 at 4 pm B&H 190

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MAY

Thursday, May 6, 2009 at 4 pm B&H 190

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Thursday, May 13, 2009

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Thursday, May 20, 2009 at 4 pm B&H 190

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Thursday, May 27, 2009 at 4 pm B&H 190

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