Eric Sembrat's Test Bonanza

Understanding the new states at the interfaces and the resulting whole behavior of the heterostructures and multilayers is a hot topic at the forefront of the fundamental research, as demonstrated by the huge number of theoretical and experimental studies published in the topmost level scientific journals. In this context, strongly electron correlated oxides are attracting an increasing attention because of their possible practical applications in the emerging field of oxide electronics [1]. With the recent advances in thin-film fabrication, controlled growth of unit-cell layers of complex oxides opened new perspectives in the study of interface effects. In fact, a wealth of microscopic phenomena may be at the work at the interface between the constituent oxides and can result in a number of novel functional properties [2]. In this seminar, I will present two particular examples of unexpected electronic and magnetic interfacial phenomena in multilayers based on complex oxides: ferromagnetism, at the interface of two antiferromagnetic insulating constituent materials [3] and superconductivity, at the interface of two insulating oxides [4]. To disentangle the role of each constituent block and disclose the mechanism giving rise to the interfacial properties, elemental sensitive spectroscopic techniques can be extremely useful. In particular, I will describe the results obtained with two state-of-art synchrotron radiation techniques, namely polarization dependent soft x-ray absorption spectroscopy and bulk sensitive hard x-ray photoelectron spectroscopy.

[1] A.P. Ramirez, Science 315, 1377 (2007); E. Dagotto, Science 318, 1076 (2007).

[2] P. Zubko et al. Annu. mso-ansi-language:EN-US">Rev. Condens. Matter. Phys. 2, 141 (2011); H. Y. Hwang et al. Nature Materials 11, 103 (2012)

[3] C. Adamo et al. Appl. mso-ansi-language:EN-US">Phys. Lett. 92, 112508 (2008); A. Bhattacharya et al. Phys. Rev. Lett. 100, 257203 (2008)

[4] EN-US;mso-fareast-language:IT">G.Balestrino et al. Phys. Rev.B 58, R8925 (1998); A. Gozar et al., Nature 455, 782-785 (2008); C. Aruta et al., Phys. mso-bidi-font-style:italic">Rev. B 78, 205120 (2008)

[5] C.Aruta et al. mso-ansi-language:EN-US">Phys. Rev. B 80, R140405 (2009)

[6] D. Di Castro et al. cond-mat arXiv:1107.2239

The workshop will provide a general introduction into numerical relativity and in code development within large collaborations.  The number of addendees are limited, and while registration is free, it is required. In order to register, write an email to workshop@einsteintoolkit.org.

We study the effect of electron-electron interaction on the resistivity of a metal where umklapp scattering is either not effective or suppressed. This can happen in cases such as in a metal near a Pomeranchuk quantum phase transition or in a system with low density of carriers, e.g., the surface states of three-dimensional (3D) topological insulators. In such cases, one must consider both interactions and disorder to obtain a finite and T dependent resistivity. The existence of the Fermi-liquid (T^2) term in resistivity of a two-dimensional (2D) metal, as we show, then depends on 1) dimension (2D vs 3D), 2) geometry (concave vs convex), and 3) topology (simply vs multiply connected) of the Fermi surface. In the case of 3D topological insulators of the Bi_2Te_3 family, upon doping the Fermi surface of 2D metallic surface states changes its shape from convex to concave due to hexagonal warping, while still being too small to allow for umklapp scattering. We show that the T^2 term in the resistivity is present only in the concave regime and demonstrate that the resistivity obeys a universal scaling form valid for an arbitrary 2D Fermi surface near a convex/concave transition.

I describe a unified approach to locating key material transport barriers in unsteady flows induced by two-dimensional, non-autonomous dynamical systems. Seeking transport barriers as minimally stretching material lines, one obtains that such barriers must be shadowed by minimal geodesics under the metric induced by the Cauchy-Green strain tensor field associated with the flow map. As a result, snapshots of transport barriers can be explicitly computed as trajectories of ordinary differential equations. Using this approach, hyperbolic barriers (generalized stable and unstable manifolds), elliptic barriers (generalized KAM curves) and parabolic barriers (generalized shear jets) can be found with high precision in temporally aperiodic flows defined over a finite time interval. I illustrate these results on unsteady flows arising in mechanics and fluid dynamics.

In this exciting event, three lectures will be presented from world renown Chef Jose Andres and Harvard Physics Professors Michael P. Brenner and David A. Weitz.  Awards will also be presented to the top Dekalb County high school student submissions for the Squishy Physics photography contest in conjunction with the Fernbank Science Center, with all the submissions on display at the event.

Most of what we eat is squishy - behaving as a solid on a plate, or as a liquid when processed in your mouth.  Squishy Physics investigates materials that are soft and easy to deform and, in most cases, are made from mixtures of phases.  The lectures will cover interesting and entertaining physical questions that are critical to cooking and understanding the properties of food.

Most of the baryons in the present universe are missing. This talk gives a historical review of the issue, followed by some highlights of current theoretical and observational effort to understand it.

Gamma-Ray Bursts (GRBs) are the brightest light sources in the Universe, as well as the most distant sources known. These characteristics, combined with their powerlaw spectra, make them ideal cosmological probes. In this talk I will discuss how GRBs are impacting several areas of extragalactic astrophysics and cosmology. In particular, I will show how they can be used to trace the evolution of the mean density and clumpiness of the interstellar medium with redshift, and the properties of dust in high-z galaxies. Detection of GRBs at very high redshifts can help set constraints on the small-scale power spectrum of density fluctuations. High-resolution observations of long GRBs allow to shed light on the properties of their massive star progenitors.  Statistical studies of short GRBs can improve our understanding of evolutionary binary scenarios.

Anderson localization (AL) is a ubiquitous interference phenomenon in which waves fail to propagate in a disordered medium.  We observe three-dimensional AL of non-interacting ultracold matter by allowing a spin-polarized atomic Fermi gas to expand into a disordered potential that is creating using optical speckle.  A two-component density distribution emerges consisting of an expanding mobile component and a non-diffusing localized component. We extract a mobility edge that increases with the disorder strength, whereas the thermally averaged localization length is shown to decrease with disorder strength and increase with particle energy. Progress toward combining disordered fermions with an optical lattice in order to realize the disordered (Fermi-) Hubbard model will be discussed.

mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">Although we now know that microorganisms rule the oceans - controlling productivity and biogeochemical cycles - we largely ignore how they are affected by typical flow conditions. Here I present microfluidic and millifluidic experiments, combined with mathematical models, to show that fluid flow can have profound effects on the biomechanics of swimming microorganisms. I illustrate this for two cases of directed motility, or 'taxis'. In the first case - 'gyrotaxis' - the coupling of hydrodynamic shear and bottom-heaviness, typical of many phytoplankton species, causes intense clustering of cells in layers and patches, which can have profound effects on population dynamics. In the second case - 'rheotaxis' - the coupling of shear and the chiral shape of bacterial flagella leads to a previously unrecognized torque on cells, which can hamper motility and thus foraging in the sea.