Events at Physics |
Events on Thursday, February 12th, 2009
- R. G. Herb Condensed Matter Seminar
- Precision Measurements of the London Penetration Depth and Pairing Symmetry in Superconductors
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Ruslan Prozorov, Iowa State University & Ames Laboratory
- Abstract: The pairing mechanism is the Holy Grail for researchers in the field of superconductivity. One of the experimentally accessible manifestations of the pairing mechanism is the structure of the superconducting gap on the Fermi surface and the corresponding behavior of low-energy quasiparticles with respect to an applied magnetic field, scattering rate, heat flow, etc. The London penetration depth is directly related to the superfluid density and, therefore, is one of the primary experimentally measurable quantities. It is also relatively easy to model for various superconducting gaps and for arbitrary scattering by using microscopic or semiclassical formalisms.
During the last 20 years, there has been remarkable progress in the development of techniques for ultra-precise measurements of the penetration depth, especially in the frequency-domain. I will briefly review the major milestones where this technique has been used--from the very first discovery of d-wave pairing in hole-doped cuprates [1] through d-wave pairing in electrondoped cuprates [2]. I will spend most of the time on today's hot topic of Fe-based pnictide superconductors for which the unconventional behavior will be demonstrated [3]. It is possible that this class of materials is one of the most complex we have ever encountered in the field of superconductivity due to complex multi-band electronic structure and substantial influence of the magnetic subsystem.
[1] W. N. Hardy et al., Phys. Rev. Lett. 70, 3999 (1993)
[2] R. Prozorov et al., Phys. Rev. Lett. 85, 3700 (2000)
[3] R. T. Gordon et al., http://arxiv.org/abs/0812.3683 - Host: Andrey Chubukov
- Atomic Seminar
- Ultracold plasma dynamics in a magnetic field
- Time: 12:00 pm
- Place: 5310 Chamberlin
- Speaker: Xianli Zhang, University of Maryland
- Abstract: Ultracold plasmas created by photoionizing a sample of laser cooled and trapped cold atoms, has extended the neutral plasma parameters by about two orders of magnitude, as the electron temperatures as low as 1 Kelvin. Previous studies focused on the study of the plasma free expansion and electron temperature evolution without a magnetic field. In this talk, I will present the first study of ultracold plasma dynamics in a magnetic field by using a newly developed time-of-flight projection imaging technique, such as plasma expansion and plasma instabilities.
- Host: Mark Saffman
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Covariance, Dynamics and Symmetries, and Hadron Physics
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Craig Roberts, Argonne National Laboratory
- Abstract: QCD's Dyson-Schwinger equations provide a continuum framework within which hadron structure and interactions can be studied. Nonperturbative, symmetry-preserving truncations exist so that model-independent predictions can be made and illustrated. Insights that this approach yields into meson and nucleon structure will be explained.
- Host: M J Ramsey-Musolf