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Events on Thursday, February 9th, 2017

R. G. Herb Condensed Matter Seminar
Two-dimensional epitaxial superconductor-semiconductor heterostructures: A platform for topological superconducting networks
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Javad Shabani , City College, City University of New York
Abstract: Progress in the emergent field of topological superconductivity relies on synthesis of new material combining superconductivity, low density, and spin-orbit coupling. For example, theory indicates that the interface between a one-dimensional semiconductor with strong spin orbit coupling and a superconductor hosts Majorana modes with nontrivial topological properties. Recently, epitaxial growth of Al on InAs nanowires was shown to yield a high quality superconductor-semiconductor (S-Sm) system with uniformly transparent interfaces and a hard induced gap, indicted by strongly suppressed subgap tunneling conductance. Here we report the realization of a two-dimensional (2D) InAs/InGaAs heterostructure with epitaxial Al, yielding a planar S-Sm system with structural and transport characteristics as good as the epitaxial wires. The realization of 2D epitaxial S-Sm systems represent a significant advance over wires, allowing extended networks via top-down processing. Among numerous potential applications, this new material system can serve as a platform for complex networks of topological superconductors with gate-controlled Majorana zero modes. We demonstrate gateable Josephson junctions and a highly transparent 2D S-Sm interface based on the product of excess current and normal state resistance.

Host: Vavilov
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Astronomy Colloquium
Insights into Galaxies using Dynamical Modeling
Time: 3:30 pm - 5:00 am
Place: 4421 Sterling Hall, Coffee and Cookies 3:30 pm. Talk Begins 3:45 PM
Speaker: Shravan Shetty, UW Madison Astronomy Department
Abstract: Understanding the underlying mass distribution of galaxies promises to unveil immense information about galaxies, however converting their observed two dimensional kinematics into three dimensional mass distributions is a degenerate problem. Various techniques have been used to create the detailed dynamical models of galaxies but the most general and reliable of these techniques tend to be computationally intensive even today and hence are applicable to only small number of galaxies. In recent years however, based on empirical results, the Jeans Anisotropic Models (JAM) have allowed astronomers to create detailed dynamical models for large number of galaxies. Using this technique, I present the results of my PhD thesis wherein I study the
evolution of galaxies with redshift and with environment.
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Neutrinos: From idea to discovery to precision measurements
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Minerba Betancourt, Fermilab
Abstract: The discovery of neutrino oscillations opened new windows for the study of neutrino physics. In this talk, I will present the history and importance of neutrino physics, concentrating on neutrinos produced by accelerator. Specifically, I will give an overview of the neutrino physics program at Fermilab and the remaining questions for the neutrino physics. In order to answer the open questions in neutrino physics, it is critical that we understand neutrino interactions and nuclear effects on these interactions extremely well. MINERvA is a neutrino scattering experiment which make precision measurements of cross sections and a studies of nuclear effects. I will present measurements of quasi-elastic scattering, which is one of the largest contributions to the signal of many oscillation experiments.
Host: Sridhara Dasu
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