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This Week at Physics

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Events on Thursday, October 6th, 2011

R. G. Herb Condensed Matter Seminar
Superconducting gap symmetry in novel superconductors: insights from quasiparticle interference
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Ilya Eremin, Ruhr-University Bochum, Germany
Abstract: Coherence factors are a hallmark of superconductivity as a pair-condensation phenomenon. When electrons pair, quasi-particles develop an acute phase sensitivity to different types of scattering potential, described by the appearance of coherence factors in the scattering amplitudes. While the effects of phase-sensitive coherence factors are well established in isotropic superconductors, they are much harder to detect in their anisotropic counterparts, such as high-Tc cuprates, iron-based superconductors, or heavy-fermion superconductors. One of the recently developed technique to determine the phase structure of the superconducting order parameter is scanning tunneling microscopy (STM) which determines the dispersion of quasiparticle states from the quasiparticle interference (QPI) patterns induced by impurity scattering. Such experiments, performed in an external magnetic field, offer the capability of probing the phase of the superconducting order parameter by detecting a field enhancement of the sign preserving scattering that results from the sensitivity of QPI to the coherence factors associated with impurity scattering. In my talk I will review the experimental and theoretical results for layered cuprates and present calculations of the QPI patterns in iron-based superconductors and heavy fermion superconductor, CeCoIn5 where the symmetries of the superconducting gaps are still actively debated.
Host: Chubukov
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Going to the ends of the earth to glimpse the beginnings of time: Observing the Big Bang with the BICEP Telescope at the South Pole
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Brian Keating, UCSD Department of Physics
Abstract: The Background Imager of Cosmic Extragalactic Polarization (BICEP) experiment is the first cosmic microwave background (CMB) polarimeter designed to measure the "B-mode" polarization of the CMB, hypothesized to originate during the Inflationary epoch. Beginning in 2006 BICEP observed 3% of the sky from our observatory at the Amundsen-Scott South Pole Research Station in Antarctica. In this colloquium I will present our initial results and discuss the unique design features of BICEP which led to the first meaningful limits on the energy scale of Inflation to come from CMB polarization. Soon after BICEP's initial results were released, a publication (Xia, Li & Zhang, 2009), claimed a first-detection of parity-violating "cosmic birefringence" effects using publicly available BICEP data. I will discuss the challenges of polarimetry at the few parts per billion level and explain why systematic effects are particularly pernicious for probes of cosmic parity violation. I will conclude by discussing how BICEP and its successor, BICEP2, currently in its second observing season at the South Pole will constrain Inflationary cosmology and future measurements of cosmic birefringence.
Host: Peter Timbie
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Graduate Introductory Seminar
Condensed Matter Theory Seminar
Time: 5:30 pm
Place: 2223 Chamberlin Hall
Speaker: Chubukov, Coppersmith, Joynt, Perkins, Vavilov
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