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This Week at Physics

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Events During the Week of March 31st through April 7th, 2013

Monday, April 1st, 2013

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:30 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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Condensed Matter Theory Group Seminar
Manifestations of electronic nematic degrees of freedom in the high-temperature iron-based superconductors
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Rafael Fernandes, University of Minnesota
Abstract: Five years after their discovery, much of the interest in iron-pnictide materials remains in understanding not only their superconducting transition at nearly 60K, but also the nature of their normal state. In this context, a hotly debated topic is the origin of the tetragonal to orthorhombic transition, which either precedes or happens simultaneously to a magnetic instability, and persists even in the vicinities of the superconducting dome. Experiments have revealed that the anisotropies in this orthorhombic phase cannot be explained by the small lattice distortion alone, suggesting that the tetragonal symmetry breaking is driven by electronic degrees of freedom, dubbed nematic in analogy to the physics of liquid crystals. In this talk, I will present a consistent microscopic theoretical model for this nematic phase and explore its manifestations in a variety of macroscopic properties of the iron pnictides -- such as elastic, magnetic, and transport properties. The model is rooted on the degeneracy of the magnetic ground state of these materials, which, allied to the coupling to the lattice and to the orbital degrees of freedom, leads to a spontaneous tetragonal symmetry breaking in the paramagnetic phase. The scattering of electrons by spin fluctuations in the nematic phase leads to an anisotropy in the resistivity, whose sign changes from electron-doped to hole-doped compounds. Finally, I will also discuss the impact of both nematic order and nematic fluctuations to the unconventional s+- superconducting state of the iron pnictides.
Host: Chubukov
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Tuesday, April 2nd, 2013

Chaos & Complex Systems Seminar
The effects of human capital depreciation on occupational gender segregation
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Hsueh-Hsiang (Cher) Li, UW Department of Economics
Abstract: This talk analyzes how human capital depreciation affects occupational gender segregation. Prior studies are generally biased because, given an occupational depreciation rate, female workers endogenously choose the duration of leave. I address this problem by proposing an alternative depreciation measure utilizing involuntary job displacement shocks. Using this depreciation proxy along with additional pecuniary and non-pecuniary occupational attributes, I estimate a conditional logit model of occupational choices separately for male and female college graduates. My results show that women have a stronger distaste than men for occupations with high human capital depreciation.<br>
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Askaryan Radio Array at the South Pole
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Michael DuVernois, University of Wisconsin IceCube
Abstract: A series of weekly presentations and discussions of current research topics in physics by the scientists involved in those studies designed to expose students to the topics and excitement of the research frontier.
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Wednesday, April 3rd, 2013

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The Variable High-Energy Gamma-Ray Sky
Time: 4:00 pm
Place: 4274 Chamberlin
Speaker: Julie McEnery, Goddard GSFC, Maryland
Abstract: The launch of the Fermi Gamma-ray Space Telescope in 2008 has ushered in a new era for the study of the extreme Universe. In addition to ground-breaking improvements in sensitivity and angular resolution, providing the deepest and sharpest view of the high-energy gamma-ray sky, Fermi also has opened a whole new window in the time domain. With a large field of view allowing complete coverage of the sky every 3 hours, Fermi can "catch" rare and exciting transient events in addition to following the behaviour of all gamma-ray emitters as a function of time. In this talk, I will review some of the surprises uncovered by Fermi on timescales from milliseconds to years and describe how these results have advanced our understanding of some of the most extreme phenomena known to astrophysics.
Host: Francis Halzen
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Thursday, April 4th, 2013

R. G. Herb Condensed Matter Seminar
Specific heat and magnetization studies of Dy2Ti2O7
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Jan Kycia, University of Waterloo
Abstract: Dy2Ti2O7 is a material with a pyrochlore lattice of corner-sharing tetrahedral. Crystal-field effects constrain the magnetic moments of the rare-earth ions to point along the axis connecting the centres of the two neighbouring tetrahedra. As a result, the magnetic moments are highly frustrated and possess a ground state containing a large residual entropy similar to water ice. Because of this similarity to water ice, the system is called a spin ice. Recently a very interesting perspective has been developed in which the thermal excitations in the magnetic spins are viewed as magnetic monopoles. In this talk, I will review some of the progress in understanding spin ice and the monopole picture. I will discuss my group's results of specific heat, ac susceptibility and magnetization measurements.
Host: McDermott
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Astronomy Colloquium
Time-Domain informatics and Smart Data Analytics in the Era of Large Astronomical Surveys
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Hakeem Oluseyi, Florida Institute of Technology
Abstract: Current and upcoming large surveys for studying dark energy and the Lambda-CDM paradigm, such as the Dark Energy Survey (DES) and the Large Synoptic Survey Telescope (LSST), will require reliable identification, classification and analyses of large numbers of transient and variable sources. One subset of these efforts are the near-field cosmology studies that map the distributions of Galactic stars in spatial-kinematic-metallicity-age space to test models of Galactic assembly and evolution. This talk will describe our work on developing new astroinfomatics techniques for taking advantage of the chromo-temporal data that will be available from the LSST and our current work with data from Kepler and LINEAR surveys.
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Friday, April 5th, 2013

Physics Department Colloquium
Nonlinear Quantum Liquids in One Dimension
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Leonid Glazman, Yale University
Abstract: The conventional description of one-dimensional quantum fluids is based on the Luttinger liquid theory. In that theory, the true energy-momentum relation of particles making up the fluid is replaced by a linear one. This simplification is crucial for the theory, and abandoning it has proven to be difficult. The talk presents a breakthrough which allowed one to circumvent the difficulty. The new theory describes dynamic responses of a fluid consisting of particles with a generic spectrum. It is applicable to a diverse group of systems, including, for example, electrons in quantum wires and cold atomic gases in one-dimensional traps.
Host: Vavilov
Poster: http://www.physics.wisc.edu/twap/posters/2013/2768.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2013/2013-04-01.pdf

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