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Center for the Science and Technology of Advanced Materials and Interfaces
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ItemDesigner Colloidal Nanocrystal Materials for Electronic and Optical Applications( 2019-03-12) Kagan, Cherie R.Semiconductor and plasmonic nanocrystals are known for their size and shape dependent photo-luminescence and localized surface plasmon resonances, respectively. In this talk, I will describe the use of semiconductor and plasmonic nanocrystals as building blocks of mesoscale materials for semiconductor electronics and optoelectronics and plasmonic optical metamaterials. Chemical exchange of the long ligands used in nanocrystal synthesis with more compact ligand chemistries brings neighboring nanocrystals into proximity and increases interparticle coupling. In semiconductor nanocrystal solids, we show strong electronic coupling in combination with doping allows us to control the carrier type and concentration to design high mobility n- and p-type materials. I will give examples where n- and p-type nanocrystal solids are used to construct field-effect transistors and integrated circuits and solar photovoltaics. In metal nanocrystals, ligand-controlled coupling allows us to tailor a dielectric-to-metal phase transition seen by a 1010 range in DC conductivity and a dielectric permittivity ranging from everywhere positive to everywhere negative across the whole range of optical frequencies. We realize a "diluted metal" with optical properties not found in the bulk metal analog, presenting a new axis in plasmonic materials design and the realization of optical properties akin to next-generation metamaterials. We harness the properties of metal nanocrystals by using nanoimprint lithography to print large-area metamaterials on glass and plastics with widely tailorable optical properties that are used to realize near-infrared optical devices.
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ItemScaling down the laws of thermodynamics(Georgia Institute of Technology, 2018-11-14) Jarzynski, ChristopherThermodynamics provides a robust conceptual framework and set of laws that govern the exchange of energy and matter. Although these laws were originally articulated for macroscopic objects, it is hard to deny that nanoscale systems, as well, often exhibit “thermodynamic-like” behavior. To what extent can the venerable laws of thermodynamics be scaled down to apply to individual microscopic systems, and what new features emerge at the nanoscale? I will review recent progress toward answering these questions, with a focus on the second law of thermodynamics. I will argue that the inequalities ordinarily used to express the second law can be replaced by stronger equalities, known as fluctuation relations, which relate equilibrium properties to far-from-equilibrium fluctuations. The discovery and experimental validation of these relations has stimulated interest in the feedback control of small systems, the closely related Maxwell demon paradox, and the interpretation of the thermodynamic arrow of time. These developments have led to new tools for the analysis of non-equilibrium experiments and simulations, and they have refined our understanding of irreversibility and the second law.
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ItemActive Fluids as Topological Metamaterials: Structure Without H Periodic Order(Georgia Institute of Technology, 2018-05-15) Souslov, AntonActive liquids are composed of self-driven microbots that endow the liquid with a unique set of mechanical characteristics. We present two designs for topological states using active fluids: one using periodic confinement and another using a bulk fluid without periodic order. In a periodic lattice, geometry of confinement controls the structure of topological waves. Without periodic order, topological edge waves can arise in a fluid of self-spinning particles undergoing spontaneous active rotation. This can occur because a fluid undergoing rotation experiences a Coriolis force that breaks Galilean invariance and opens a gap at low frequency. Alternatively, such edge waves can arise due to a Lorentz force in a magnetized plasma. We explore the interplay of topological states and an anomalous response coefficient called odd (or Hall) viscosity. For large odd viscosity, this transverse response can be measured via the profile shape of topologically robust edge waves.
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ItemObservation of Optical Weyl Points and Other Topics in Topological Photonics(Georgia Institute of Technology, 2018-05-15) Rechtsman, Mikael C.
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ItemHigher Order Topological Insulators: Quadrupoles and Beyond(Georgia Institute of Technology, 2018-05-15) Hughes, Taylor
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ItemDefect Unbinding in Active Nematic Tori(Georgia Institute of Technology, 2018-05-15) Fernandez-Nieves, AlbertoWe will discuss our recent results with active nematics on toroidal surfaces and show how, despite the intrinsic activity and out-of-equilibrium character of our system, we still observe remnants of the expected curvature-induced defect unbinding predicted for nematics in their ground state. In our experiments, however, the number of defects is far larger than what one would expect for conventional nematics. In addition, these defects move throughout the toroidal surface and explore "phase space", bringing about interesting analogies with what we could call the high-temperature limit of a nematic liquid crystal. We unravel the role of activity by comparing our results to numerical simulations. Overall, our results illustrate the interplay between order, topological constraints, local geometry and activity.
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ItemTopological Edge Floppy Modes in Disordered Fiber Networks(Georgia Institute of Technology, 2018-05-14) Mao, XiaomingDisordered fiber networks are ubiquitous in natural and manmade materials. The dilute nature of these networks permits floppy modes which only bend the fibers without changing their length, and these floppy modes govern mechanical response of the material. In this talk, we show that the geometry of the fiber network dictates the nature of these floppy modes. In particular, an ideal network in which all fibers are straight hosts bulk floppy modes, whereas perturbing the network geometry induces floppy modes exponentially localize on the edge of the network. Various activities present in fiber networks, such as active driving of motors in the cytoskeleton and actuators in manmade fiber networks, could lead to such edge floppy modes. We show that the localization of these edge floppy modes is protected by the topology of the phonon structure of the fiber networks, analogous to topological edge floppy modes in Maxwell lattices.
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ItemVibration Location in Quasi-Periodic Beams and Plates(Georgia Institute of Technology, 2018-05-14) Ruzzene, MassimoThe talk will present ongoing investigations on elastic wave propagation in quasi-periodic beams and plates. Results show the occurrence of a variety of modes that are localized at the edges or within the quasi-periodic arrangement of mass and stiffness inclusions. The areas in which localization occurs can be predicted by the evaluation of the quasi-static (zero frequency) response of the system, that defines domains boundaries that constrain the localization regions and thus delineate them. The talk will present numerical results that illustrate the behavior of the considered class of systems, along with ongoing experimental investigations that demonstrate some of the unique features predicted by theoretical findings.
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ItemPersistence of Topological Invariants Under Disorder(Georgia Institute of Technology, 2018-05-14) Bellissard, JeanA review of the techniques on Non-commutative Geometry to express rigorously the topological invariants, like in the Quantum Hall Effect or Topological Insulators will be provided. It will include some numerical work by Emil Prodan based on these techniques. It will be shown that these invariants are associated with K-theory and are robust under adding disorder to the system under study.
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ItemTopological Protected Modes in Non-equilibrium Stochastic Systems(Georgia Institute of Technology, 2018-05-14) Vaikuntanathan, SuriNon-equilibrium driving of biophysical processes is believed to enable their robust functioning despite the presence of thermal fluctuations and other sources of disorder. Such robust functions include sensory adaptation, enhanced enzymatic specificity and maintenance of coherent oscillations. Elucidating the relation between energy consumption and organization remains an important and open question in non-equilibrium statistical mechanics. Here we report that steady states of systems with non-equilibrium fluxes can support topologically protected boundary modes that resemble similar modes in electronic and mechanical systems. Akin to their electronic and mechanical counterparts, topological-protected boundary steady states in non-equilibrium systems are robust and are largely insensitive to local perturbations. We argue that our work provides a framework for how biophysical systems can use non-equilibrium driving to achieve robust function.